First, I’ll describe the principle of operation. properly made insulated roof, after which it will be easier to understand the reasons for the appearance of condensation on the vapor barrier - pos. 8.
If you look at the picture above - “Insulated roof with slate”, then vapor barrier placed under the insulation in order to retain water vapor from inside the room, and thereby protect the insulation from getting wet. For complete tightness, the joints of the vapor barrier are glued vapor barrier tape. As a result, vapors accumulate under the vapor barrier. In order for them to erode and not soak the internal lining (for example, gypsum plasterboard), between the vapor barrier and internal lining a gap of 4 cm is left. The gap is ensured by laying the sheathing.
The insulation on top is protected from getting wet waterproofing material. If the vapor barrier under the insulation is laid according to all the rules and is perfectly sealed, then there will be no vapors in the insulation itself and, accordingly, under the waterproofing too. But in case the vapor barrier suddenly gets damaged during installation or during operation of the roof, a space is made between the waterproofing and insulation ventilation gap. Because even the slightest, invisible damage to the vapor barrier allows water vapor to penetrate into the insulation. Passing through the insulation, vapors accumulate on inner surface waterproofing film. Therefore, if the insulation is laid close to waterproofing film, then it will get wet from water vapor accumulated under the waterproofing. To prevent this wetting of the insulation, as well as for the vapors to erode, there must be a ventilation gap of 2-4 cm between the waterproofing and the insulation.
Now let's look at the structure of your roof.
Before you laid insulation 9, as well as vapor barrier 11 and gypsum board 12, water vapor accumulated under vapor barrier 8, there was free access of air from below and they evaporated, so you did not notice them. Up to this point, you essentially had the correct roof design. Once you've laid additional insulation 9 close to the existing vapor barrier 8, water vapor had nowhere else to go except to be absorbed into the insulation. Therefore, these vapors (condensation) became noticeable to you. A few days later, you laid vapor barrier 11 under this insulation and sewed up gypsum board 12. If you laid the lower vapor barrier 11 according to all the rules, namely with an overlap of at least 10 cm and taped all joints with vapor-proof tape, then water vapor will not penetrate into the roof structure and will not the insulation will be soaked. But before this lower vapor barrier 11 was laid, insulation 9 had to dry out. If it has not had time to dry, then there is a high probability of mold forming in the insulation 9. This also threatens the insulation 9 in the event of the slightest damage to the lower vapor barrier 11. Because the steam will have nowhere to go except to accumulate under the vapor barrier 8, soaking the insulation and promoting the formation of fungus in it. Therefore, in an amicable way, you need to completely remove the vapor barrier 8, and make a ventilation gap of 4 cm between the vapor barrier 11 and the gypsum board 12, otherwise the gypsum board will get wet and bloom over time.
Now a few words about waterproofing. First, roofing felt is not intended for waterproofing pitched roofs; it is a bitumen-containing material and in extreme heat the bitumen will simply flow down to the roof overhang. In simple words, roofing felt will not last long in a pitched roof, it’s hard to even say how long, but I don’t think it will last more than 2 - 5 years. Second, the waterproofing (roofing felt) was not installed correctly. There must be a ventilation gap between it and the insulation, as described above. Considering that the air in the under-roof space moves from the overhang to the ridge, the ventilation gap is provided either by the fact that the rafters are higher than the layer of insulation laid between them (the rafters in your picture are just higher), or by laying counter-lattice along the rafters. Your waterproofing is laid on the sheathing (which, unlike the counter-lattice, lies across the rafters), so all the moisture that accumulates under the waterproofing will soak the sheathing and it will also not last long. Therefore, in an amicable way, the top of the roof also needs to be redone: replace roofing felt with waterproofing film, and lay it on the rafters (if they protrude at least 2 cm above the insulation) or on a counter-lattice laid along the rafters.
Ask clarifying questions.
Let's say a word about the transformer
For a newbie in power electronics, a transformer is one of the most confusing subjects.
- It is not clear why a Chinese welding machine has a small transformer on an E55 core, produces a current of 160 A and feels great. But in other devices it costs twice as much for the same current and gets incredibly hot.
- It’s not clear: is it necessary to make a gap in the transformer core? Some say it is beneficial, others believe the gap is harmful.
What number of turns is considered optimal? What induction in the core can be considered acceptable? And much more is also not entirely clear.
In this article I will try to clarify frequently arising questions, and the purpose of the article is not to obtain a beautiful and incomprehensible calculation method, but to more fully familiarize the reader with the subject of discussion, so that after reading the article he has a better idea of what can be expected from a transformer, and what to pay attention to when choosing and calculating it. How this will turn out is up to the reader to judge.
Where to begin?
Usually they start with choosing a core to solve a specific problem.
To do this, you need to know something about the material from which the core is made, about the characteristics of the cores made from this material various types, and the more the better. And, of course, you need to imagine the requirements for the transformer: what it will be used for, at what frequency, what power it should deliver to the load, cooling conditions, and, perhaps, something specific.
Just ten years ago, to obtain acceptable results it was necessary to have many formulas and carry out complex calculations. Not everyone wanted to do routine work, and the design of a transformer was most often carried out using a simplified method, sometimes at random, and, as a rule, with some reserve, which was even given a name that well reflected the situation - “fright coefficient”. And, of course, this coefficient is included in many recommendations and simplified calculation formulas.
Today the situation is much simpler. All routine calculations are included in programs with a user-friendly interface. Manufacturers of ferrite materials and cores lay out detailed characteristics their products and offer software for selecting and calculating transformers. This allows you to fully use the capabilities of the transformer and use a core of exactly the size that will provide the required power, without the coefficient mentioned above.
And you need to start by modeling the circuit in which this transformer is used. From the model you can take almost all the initial data for calculating the transformer. Then you need to decide on the manufacturer of the cores for the transformer and obtain full information about its products.
This article will use modeling in a freely available program and its updating as an example. LTspice IV, and as a core manufacturer - the well-known Russian company EPCOS, which offers the "Ferrite Magnetic Design Tool" program for selecting and calculating its cores
Transformer selection process
We will select and calculate a transformer using the example of using it in a welding power source for a semi-automatic machine, designed for a current of 150 A at a voltage of 40 V, powered by three-phase network.
The product of an output current of 150 A and an output voltage of 40 V gives the device output power Pout = 6000 W. The efficiency of the output part of the circuit (from transistors to the output) can be taken equal toEfficiency out = 0.98. Then the maximum power supplied to the transformer is
Rtrmax = Pout / Efficiencyout = 6000 W / 0.98 = 6122 W.
We choose the switching frequency of the transistors to be 40 - 50 KHz. In this particular case, it is optimal. To reduce the size of the transformer, the frequency must be increased. But a further increase in frequency leads to an increase in losses in the circuit elements and, when powered from a three-phase network, can lead to electrical breakdown of the insulation in an unpredictable place.
In Russia, the most available type E ferrites are made from N87 material from EPCOS.
Using the Ferrite Magnetic Design Tool program, we will determine the core suitable for our case:
Let us immediately note that the definition will be an estimate, since the program assumes a bridge rectification circuit with one output winding, and in our case, a rectifier with a midpoint and two output windings. As a result, we should expect a slight increase in current density compared to what we included in the program.
The most suitable core is E70/33/32 made of N87 material. But in order for it to transmit a power of 6 kW, it is necessary to increase the current density in the windings to J = 4 A/mm 2, allowing greater copper overheating dTCu[K] and put the transformer in a blower to reduce the thermal resistance Rth[° C/ W] to Rth = 4.5 °C/W.
For correct use core, you need to familiarize yourself with the properties of the N87 material.
From the graph of permeability versus temperature:
it follows that the magnetic permeability first increases to a temperature of 100 ° C, after which it does not increase until a temperature of 160 ° C. In the temperature range from 90° C to 160 ° C changes by no more than 3%. That is, transformer parameters that depend on magnetic permeability in this temperature range are most stable.
From the hysteresis plots at temperatures of 25 ° C and 100 ° C:
it can be seen that the range of induction at a temperature of 100 ° C is less than at a temperature of 25 ° C. It should be taken into account as the most unfavorable case.
From the graph of losses versus temperature:
It follows that at a temperature of 100 ° C, losses in the core are minimal. The core is adapted to operate at a temperature of 100 ° C. This confirms the need to use the properties of the core at a temperature of 100 ° C when modeling.
The properties of the E70/33/32 core and N87 material at a temperature of 100 ° C are given in the tab:
We use this data to create a model of the power part of the welding current source.
Model file: HB150A40Bl1.asc
Drawing;
The figure shows a model of the power part of the half-bridge power supply circuit semi-automatic welding machine, designed for a current of 150 A at a voltage of 40 V powered from a three-phase network.
The lower part of the figure represents the " " model. ( description of the operation of the protection scheme in .doc format). Resistors R53 - R45 are a model of variable resistor RP2 for setting the cycle-by-cycle protection current, and resistor R56 corresponds to resistor RP1 for setting the magnetizing current limit.
The U5 element called G_Loop is a useful addition to LTspice IV from Valentin Volodin, which allows you to view the transformer hysteresis loop directly in the model.
We will obtain the initial data for calculating the transformer in the most difficult mode for it - with minimal permissible voltage power supply and maximum PWM filling.
The figure below shows the oscillograms: Red - output voltage, blue - output current, green - current in the primary winding of the transformer.
It is also necessary to know the root mean square (RMS) currents in the primary and secondary windings. To do this, we will again use the model. Let us select the current graphs in the primary and secondary windings in steady state:
We move the cursor over the inscriptions one by oneat the top of I(L5) and I(L7) and with the "Ctrl" key pressed, click the left mouse button. In the window that appears we read: the RMS current in the primary winding is equal (rounded)
Irms1 = 34 A,
and in the secondary -
Irms2 = 102 A.
Let us now look at the hysteresis loop in steady state. To do this, click the left mouse button in the label area on the horizontal axis. The insert appears:
Instead of the word "time" in the upper window we write V(h):
and click "OK".
Now on the model diagram, click on pin “B” of element U5 and observe the hysteresis loop:
On the vertical axis, one volt corresponds to an induction of 1T; on the horizontal axis, one volt corresponds to the field strength in 1 A/m.
From this graph we need to take the induction range, which, as we see, is equal to
dB = 4 00 mT = 0.4 T (from - 200 mT to +200 mT).
Let's return to the Ferrite Magnetic Design Tool program, and on the "Pv vs. f,B,T" tab we will look at the dependence of losses in the core on the induction range B:
Note that at 100 Mt the losses are 14 kW/m3, at 150 mT - 60 kW/m3, at 200 mT - 143 kW/m3, at 300 mT - 443 kW/m3. That is, we have an almost cubic dependence of losses in the core on the induction range. For a value of 400 mT, losses are not even given, but knowing the dependence, one can estimate that they will amount to more than 1000 kW/.m 3. It is clear that such a transformer will not work for a long time. To reduce the induction swing it is necessary either to increase the number of turns in the transformer windings or to increase the conversion frequency. A significant increase in the conversion frequency in our case is undesirable. An increase in the number of turns will lead to an increase in current density and corresponding losses - according to a linear dependence on the number of turns, the induction range also decreases according to a linear dependence, but a decrease in losses due to a decrease in the induction range - according to a cubic dependence. That is, in the case where the losses in the core are significant more losses in wires, increasing the number of turns has a great effect in reducing overall losses.
Let's change the number of turns in the transformer windings in the model:
Model file: HB150A40Bl2.asc
Drawing;
The hysteresis loop in this case looks more encouraging:
The induction range is 280 mT. You can go even further. Let's increase the conversion frequency from 40 kHz to 50 kHz:
Model file: HB150A40Bl3.asc
Drawing;
And the hysteresis loop:
The induction range is
dB = 22 0 mT = 0.22 T (from - 80 mT to +140 mT).
Using the graph on the "Pv vs. f,B,T" tab, we determine the magnetic loss coefficient, which is equal to:
Pv = 180 kW/m 3 .= 180 * 10 3 W/m 3 .
And, taking the core volume value from the core properties tab
Ve = 102000 mm 3 = 0.102 * 10 -3 m 3, we determine the value of magnetic losses in the core:
Pm = Pv * Ve = 180 * 10 3 W/m 3 * 0.102 * 10 -3 m 3 .= 18.4 W.
We now set a sufficiently long simulation time in the model to bring its state closer to the steady state, and again determine the root-mean-square values of the currents in the primary and secondary windings of the transformer:
Irms1 = 34 A,
and in the secondary -
Irms2 = 100 A.
We take from the model the number of turns in the primary and secondary windings of the transformer:
N1 = 12 turns,
N2 = 3 turns,
and determine the total number of ampere turns in the transformer windings:
NI = N1 * Irms1 + 2 * N2 * Irms2 = 12 vit * 34 A + 2 * 3 vit * 100 A = 1008 A*vit.
In the topmost picture, on the Ptrans tab, in the left bottom corner The rectangle shows the recommended value for the core window fill factor with copper for this core:
fCu = 0.4.
This means that with such a fill factor, the winding must be placed in the core window, taking into account the frame. Let's take this value as a guide to action.
Taking the window cross-section from the core properties tab An = 445 mm 2, we determine the total permissible cross-section of all conductors in the frame window:
SCu = fCu*An
and determine what current density in the conductors must be allowed for this:
J = NI / SCu = NI / fCu * An = 1008 A*vit / 0.4 * 445 mm 2 = 5.7 A*vit/mm 2 .
Dimension means that regardless of the number of turns in the winding, for each square millimeter copper should account for 5.7 A of current.
Now you can move on to the design of the transformer.
Let's return to the very first figure - the Ptrans tab, according to which we estimated the power of the future transformer. It has a parameter Rdc/Rac, which is set to 1. This parameter takes into account the way the windings are wound. If the windings are wound incorrectly, its value increases and the power of the transformer decreases. Research on how to properly wind a transformer has been carried out by many authors; I will only give conclusions from these works.
First - instead of one thick wire for winding high-frequency transformer, it is necessary to use a bundle of thin wires. Because the working temperature assumed to be around 100 ° C, the wire for the harness must be heat-resistant, for example, PET-155. The tourniquet should be slightly twisted, and ideally it should be a LITZ strand twist. In practice, a twist of 10 turns per meter of length is sufficient.
Secondly, next to each layer of the primary winding there should be a layer of the secondary. With this arrangement of windings, currents in adjacent layers flow in opposite directions and the magnetic fields created by them are subtracted. Accordingly, the total field and the harmful effects it causes are weakened.
Experience shows that if these conditions are met,at frequencies up to 50 kHz the parameter Rdc/Rac can be considered equal to 1.
To form the bundles, we will choose PET-155 wire with a diameter of 0.56 mm. It is convenient because it has a cross section of 0.25 mm 2. If we reduce it to turns, each turn of the winding from it will add a cross-section Spr = 0.25 mm 2 /vit. Based on the obtained permissible current density J = 5.7 Avit/mm 2, it is possible to calculate how much current should flow per core of this wire:
I 1zh = J * Spr = 5.7 A*vit/mm 2 * 0.25 mm 2 /vit = 1.425 A.
Based on the current values Irms1 = 34 A in the primary winding and Irms2 = 100 A in the secondary windings, we determine the number of cores in the bundles:
n1 = Irms1 / I 1zh = 34 A / 1.425 A = 24 [cores],
n2 = Irms2 / I 1g = 100 A / 1.425 A = 70 [core]. ]
Let's calculate the total number of cores in the cross-section of the core window:
Nzh = 12 turns * 24 cores + 2 * (3 turns * 70 cores) = 288 cores + 420 cores = 708 cores.
Total wire cross-section in the core window:
Sm = 708 cores * 0.25 mm 2 = 177 mm 2
We will find the coefficient of filling the core window with copper by taking the window cross-section from the properties tab An = 445 mm 2 ;
fCu = Sm / An = 177 mm 2 / 445 mm 2 = 0.4 - the value from which we proceeded.
Taking the average length of the turn for the E70 frame equal to lв = 0.16 m, we determine the total length of the wire in terms of one core:
lpr =lv * Nzh,
and, knowing the conductivity of copper at a temperature of 100 ° C, p = 0.025 Ohm*mm 2 / m, we determine the total resistance of a single-core wire:
Rpr = r * lpr / Spr = r * lv * Nl/Spr = 0.025 Ohm*mm 2 / m * 0.16 m * 708 cores / 0.25 mm 2 = 11 Ohm.
Based on the fact that the maximum current in one core is equal to I 1zh = 1.425 A, we determine the maximum power loss in the transformer winding:
Prev = I 2 1zh * Rpr = (1.425 A) 2 * 11 Ohm = 22 [W].
Adding to these losses the previously calculated power of magnetic losses Pm = 18.4 W, we obtain the total power of losses in the transformer:
Psum = Pm + Pext = 18.4 W + 22 W = 40.4 W.
The welding machine cannot operate continuously. During the welding process there are pauses during which the machine “rests”. This moment is taken into account by a parameter called PN - load percentage - the ratio of the total welding time over a certain period of time to the duration of this period. Typically, for industrial welding machines, Pn = 0.6 is accepted. Taking into account Mon, the average power losses in the transformer will be equal to:
Rtr = Psum * PN = 40.4 W * 0.6 = 24 W.
If the transformer is not blown, then, taking the thermal resistance Rth = 5.6 ° C/W, as indicated on the Ptrans tab, we obtain the transformer overheating equal to:
Tper = Rtr * Rth = 24 W * 5.6 ° C/W = 134 ° C.
This is a lot, it is necessary to use forced airflow of the transformer. A generalization of data from the Internet on the cooling of ceramic products and conductors shows that when blown, their thermal resistance, depending on the air flow speed, first drops sharply and already at an air flow speed of 2 m/sec is 0.4 - 0.5 of the state rest, then the falling speed decreases, and a flow speed of more than 6 m/sec is impractical. Let's take the reduction factor equal to Kobd = 0.5, which is quite achievable when using a computer fan, and then the expected overheating of the transformer will be:
Tperobd = Rtr * Rth * Kobd = 32 W * 5.6 ° C/W * 0.5 = 67 ° C.
This means that at maximum permissible temperature environment Tormax = 40°C and at full load welding machine The heating temperature of the transformer can reach the value:
Ttrmax = Tormax + Tper = 40 ° C + 67 ° C = 107 ° C.
This combination of conditions is unlikely, but it cannot be excluded. The most reasonable thing would be to install a temperature sensor on the transformer, which will turn off the device when the transformer reaches a temperature of 100 ° C and turn it on again when the transformer cools to a temperature of 90 ° C. Such a sensor will protect the transformer even if the blowing system is disrupted.
Attention should be paid to the fact that the above calculations are made on the assumption that during breaks between welding the transformer does not heat up, but only cools down. But if special measures are not taken to reduce the pulse duration in idle mode, then even in the absence of a welding process, the transformer will be heated by magnetic losses in the core. In the case under consideration, the overheating temperature will be, in the absence of airflow:
Tperxx = Pm * Rth = 18.4 W * 5.6 ° C/W * 0.5 = 103 ° C,
and when blowing:
Tperkhobd = Pm * Rth * Kobd = 18.4 W * 5.6 ° C/W * 0.5 = 57 ° C.
In this case, the calculation should be carried out based on the fact that magnetic losses occur all the time, and losses in the winding wires are added to them during the welding process:
Psum1 = Pm + Pext * PN = 18.4 W + 22 W * 0.6 = 31.6 W.
The overheating temperature of the transformer without blowing will be equal to
Tper1 = Psum1 * Rth = 31.6 W * 5.6 ° C/W = 177 ° C,
and when blowing:
Tper1obd = Psum1 * Rth * Kobd = 31.6 W * 5.6 ° C/W = 88 ° C.
Ventilation gap in frame house- this is a moment that often raises many questions among people who are involved in insulating their own home. These questions arise for a reason, since the need for a ventilation gap is a factor that has a huge number of nuances, which we will talk about in today’s article.
The gap itself is the space that is located between the sheathing and the wall of the house. A similar solution is implemented using bars that are attached on top of the wind barrier membrane and on the external finishing elements. For example, the same siding is always attached to bars that make the facade ventilated. A special film is often used as insulation, with the help of which the house, in fact, is completely wrapped.
Many will rightly ask, is it really not possible to just take and attach the sheathing directly to the wall? Do they just line up and form an ideal area for installing sheathing? In fact, there are a number of rules that determine the necessity or unnecessaryness of organizing a ventilation facade. Let's figure out whether a ventilation gap is needed in a frame house?
When is a ventilation gap (vent gap) needed in a frame house?
So, if you are thinking about whether a ventilation gap is needed in the facade of your carcass house, pay attention to the following list:
- When wet If the insulation material loses its properties when wet, then a gap is necessary, otherwise all work, for example, on insulating a home, will be completely in vain
- Steam Permeation The material from which the walls of your home are made allows steam to pass through into the outer layer. Here, without organizing free space between the surface of the walls and insulation, it is simply necessary.
- Preventing excess moisture One of the most common questions is the following: is there a need for a ventilation gap between vapor barriers? If the finish is a vapor barrier or moisture-condensing material, it must be constantly ventilated so that excess water is not retained in its structure.
As for the last point, the list of similar models includes following types sheathing: vinyl and metal siding, profiled sheets. If they are tightly sewn onto a flat wall, then the remaining accumulated water will have nowhere to escape. As a result, materials quickly lose their properties and also begin to deteriorate externally.
Is there a need for a ventilation gap between siding and OSB?
When answering the question of whether a ventilation gap is needed between the siding and OSB (from English - OSB), it is also necessary to mention its need. As already stated, siding is a product that insulates vapor and OSB board consists entirely of wood shavings, which easily accumulates residual moisture and can quickly deteriorate under its influence.
Additional reasons to use a ventilation gap
Let's look at a few more mandatory points when clearance is a necessary aspect:
- Preventing rot and cracks The wall material under the decorative layer is prone to deformation and deterioration when exposed to moisture. To prevent rot and cracks from forming, just ventilate the surface, and everything will be fine.
- Preventing condensation The material of the decorative layer may contribute to the formation of condensation. This excess water must be removed immediately.
For example, if the walls of your house are made of wood, then an increased level of moisture will negatively affect the condition of the material. Wood swells, begins to rot, and microorganisms and bacteria can easily settle inside it. Of course, a small amount of moisture will collect inside, but not on the wall, but on a special metal layer, from which the liquid begins to evaporate and be carried away with the wind.
Is there a need for a ventilation gap in the floor? No
Here you need to take into account several factors that determine whether you need to make a gap in the floor:
- If both floors of your house are heated, then a gap is not necessary If only the 1st floor is heated, then it is enough to lay a vapor barrier on its side to prevent condensation from forming in the ceilings.
- The ventilation gap must be attached only to the finished floor!
When answering the question of whether a ventilation gap is needed in the ceiling, it should be noted that in other cases this idea is purely optional and also depends on the material chosen for insulating the floor. If it absorbs moisture, then ventilation is simply necessary.
When a ventilation gap is not needed
Below are a few cases where this construction aspect does not need to be implemented:
- If the walls of the house are made of concrete If the walls of your house are made, for example, of concrete, then you don’t need to make a ventilation gap, because this material does not allow steam to pass from the room to the outside. Consequently, there will be nothing to ventilate.
- If there is a vapor barrier inside the room If a vapor barrier was installed on the inside of the room, then the gap also does not need to be organized. Excess moisture simply will not come out through the wall, so there is no need to dry it.
- If the walls are treated with plaster If your walls are treated e.g. facade plaster, then the gap is not needed. In case outer material processing allows steam to pass through well, additional measures It is not required to ventilate the casing.
Installation example without ventilation gap
As a small example Let's look at an example of installation without the need for a ventilation gap:
- At the beginning there is a wall
- Insulation
- Special reinforcing mesh
- Mushroom dowel used for fastening
- Facade plaster
Thus, any amounts of steam that penetrate the structure of the insulation will be immediately removed through the layer of plaster, as well as through vapor-permeable paint. As you may have noticed, there are no gaps between the insulation and the decoration layer.
We answer the question why a ventilation gap is needed
The gap is necessary for air convection, which can dry out excess moisture and have a positive effect on the safety of building materials. The very idea of this procedure is based on the laws of physics. Ever since school we have known that warm air always goes up and cold always goes down. Consequently, it is always in a circulating state, which prevents liquid from settling on surfaces. In the upper part, for example, of the siding, perforations are always made, through which steam escapes out and does not stagnate. Everything is very simple!
| 7 years ago | tanya (Builderclub expert) First, I’ll describe the principle of operation. properly made insulated roof, after which it will be easier to understand the reasons for the appearance of condensation on the vapor barrier - pos. 8. If you look at the picture above - “Insulated roof with slate”, then vapor barrier placed under the insulation in order to retain water vapor from inside the room, and thereby protect the insulation from getting wet. For complete tightness, the joints of the vapor barrier are taped with vapor barrier tape. As a result, vapors accumulate under the vapor barrier. To ensure that they erode and do not soak the internal lining (for example, gypsum board), a gap of 4 cm is left between the vapor barrier and the internal lining. The gap is ensured by laying the sheathing. The insulation on top is protected from getting wet waterproofing material. If the vapor barrier under the insulation is laid according to all the rules and is perfectly sealed, then there will be no vapors in the insulation itself and, accordingly, under the waterproofing too. But in case the vapor barrier is suddenly damaged during installation or during operation of the roof, a ventilation gap is created between the waterproofing and insulation. Because even the slightest, invisible damage to the vapor barrier allows water vapor to penetrate into the insulation. Passing through the insulation, vapors accumulate on the inner surface of the waterproofing film. Therefore, if the insulation is laid close to the waterproofing film, it will get wet from the water vapor accumulated under the waterproofing. To prevent this wetting of the insulation, as well as for the vapors to erode, there must be a ventilation gap of 2-4 cm between the waterproofing and the insulation. Now let's look at the structure of your roof. Before you laid insulation 9, as well as vapor barrier 11 and gypsum board 12, water vapor accumulated under vapor barrier 8, there was free access of air from below and they evaporated, so you did not notice them. Up to this point, you essentially had the correct roof design. As soon as you laid the additional insulation 9 close to the existing vapor barrier 8, the water vapor had nowhere else to go except to be absorbed into the insulation. Therefore, these vapors (condensation) became noticeable to you. A few days later, you laid vapor barrier 11 under this insulation and sewed up gypsum board 12. If you laid the lower vapor barrier 11 according to all the rules, namely with an overlap of at least 10 cm and taped all joints with vapor-proof tape, then water vapor will not penetrate into the roof structure and will not the insulation will be soaked. But before this lower vapor barrier 11 was laid, insulation 9 had to dry out. If it has not had time to dry, then there is a high probability of mold forming in the insulation 9. This also threatens the insulation 9 in the event of the slightest damage to the lower vapor barrier 11. Because the steam will have nowhere to go except to accumulate under the vapor barrier 8, soaking the insulation and promoting the formation of fungus in it. Therefore, in an amicable way, you need to completely remove the vapor barrier 8, and make a ventilation gap of 4 cm between the vapor barrier 11 and the gypsum board 12, otherwise the gypsum board will get wet and bloom over time. Now a few words about waterproofing. First, roofing felt is not intended for waterproofing pitched roofs; it is a bitumen-containing material and in extreme heat the bitumen will simply flow down to the roof overhang. In simple words, roofing felt will not last long in a pitched roof, it’s hard to even say how long, but I don’t think it will last more than 2 - 5 years. Second, the waterproofing (roofing felt) was not installed correctly. There must be a ventilation gap between it and the insulation, as described above. Considering that the air in the under-roof space moves from the overhang to the ridge, the ventilation gap is provided either by the fact that the rafters are higher than the layer of insulation laid between them (the rafters in your picture are just higher), or by laying counter-lattice along the rafters. Your waterproofing is laid on the sheathing (which, unlike the counter-lattice, lies across the rafters), so all the moisture that accumulates under the waterproofing will soak the sheathing and it will also not last long. Therefore, in an amicable way, the top of the roof also needs to be redone: replace the roofing felt with a waterproofing film, and lay it on the rafters (if they protrude at least 2 cm above the insulation) or on a counter-lattice laid along the rafters. Ask clarifying questions. answer |
To reduce the costs associated with heating your home, it is certainly worth investing in wall insulation. Before delving into the search for a team of façade designers, it is advisable to prepare properly. Here is a list of the most common mistakes that can be made when insulating a house.
Absence or poorly executed wall insulation project
The main task of the project is to determine the optimal thermal insulation material (mineral wool or polystyrene foam) and its thickness in accordance with building codes. Also, a pre-prepared house insulation project gives the customer the opportunity to clearly control the work performed by contractors, for example, the layout of insulation sheets and the number of fasteners on square meter, and workarounds window openings, as well as much more.
Carrying out work at temperatures below 5° or above 25°, or during precipitation
The consequence of this is that the glue between the insulation and the base dries too quickly, as a result of which the adhesion between the layers of the wall insulation system is not reliable.
Ignoring site preparation
The contractor must protect all windows from dirt by covering them with film. In addition, (especially when insulating large buildings) it is good if the scaffolding is covered with a mesh, which will protect the insulated facade from excessive sunlight and wind, allowing finishing materials dry more evenly.
Insufficient surface preparation
The surface of the insulated wall must have sufficient bearing capacity and be smooth, level and free of dust to ensure good adhesion for the adhesive. Uneven plaster and any other defects must be corrected. It is unacceptable to leave mold, efflorescence, etc. residues on insulated walls. Of course, it is necessary to first eliminate the cause of their occurrence and remove them from the wall.
No starting bar
By installing the base profile, the level of the bottom layer of insulation is set. This bar also takes on part of the load from the weight. thermal insulation material. And, in addition, such a strip helps protect the lower end of the insulation from the penetration of rodents
There should be a gap of about 2-3 mm between the slats.
Installation of slabs is not staggered.
A common problem is the appearance of gaps between slabs.
The insulation slabs must be installed carefully and tightly in a checkerboard pattern, that is, offset by half the length of the slab from bottom to top, starting from the corner wall.
Incorrect application of glue
It is incorrect when gluing is carried out only by applying “bloopers” and does not apply a layer of glue around the perimeter of the sheet. The consequence of such gluing may be the bending of the insulation boards or the marking of their contour on finishing insulated facade.
Options correct application glue for foam plastic:
- along the perimeter in the form of stripes with a width of 4-6 cm. On the remaining surface of the insulation - dotted “bloopers” (from 3 to 8 pieces). The total area of the adhesive should cover at least 40% of the foam sheet;
- applying glue to the entire surface with a ridge spatula - used only if the walls are pre-plastered.
Note: the adhesive solution is applied only to the surface of the thermal insulation, never to the base.
Gluing mineral wool requires preliminary puttying of the slab surface. Thin layer cement mortar rub into the surface of the mineral wool.
Insufficient fastening of thermal insulation to the load-bearing surface
This may be the result of careless application of adhesive, the use of materials with inappropriate parameters, or too weak mechanical fastening. Mechanical connections are all kinds of dowels and anchors. Do not skimp on the mechanical fastening of insulation, be it heavy mineral wool or lightweight foam.
The place of fastening with a dowel must coincide with the place where the glue (blooper) is applied on the inside of the insulation
The dowels must be properly embedded in the insulation. Pressing too deeply leads to damage to the insulation boards and the formation of a cold bridge. Too small and it will cause a bulge that will be visible on the façade.
Leaving thermal insulation unprotected from weather conditions.
Exposed mineral wool easily absorbs water, and polystyrene foam in the sun is subject to surface erosion, which can impair the adhesion of wall insulation layers. Thermal insulation materials must be protected from atmospheric influences, both when they are stored on a construction site and when they are used to insulate walls. Walls, insulated mineral wool, must be protected by a roof to prevent them from getting wet by rain - because if this happens, they will dry very slowly, and wet insulation is not effective. Walls insulated with foam plastic cannot be exposed to prolonged exposure to direct sun rays. By long-term we mean more than 2-3 months.
Incorrect laying of insulation boards in the corners of openings
To insulate walls in the corners of window or door openings, the insulation must be cut appropriately so that the intersection of the slabs does not occur at the corners of the openings. This, of course, significantly increases the amount of waste thermal insulation material, but can significantly reduce the risk of cracks in the plaster in these places.
Not sanding the glued foam layer
This operation takes a long time and is quite labor intensive. For this reason, it is not popular among contractors. As a result, curvature may form on the facade.
Mistakes when laying fiberglass mesh
The reinforcing layer of wall insulation provides protection from mechanical damage. It is made from fiberglass mesh and reduces thermal deformation, increases strength and prevents the formation of cracks.
The mesh must be completely immersed in the adhesive layer. It is important that the mesh is glued without folds.
In places vulnerable to loads, an additional layer of reinforcement is performed - in all corners of window and door openings, strips of mesh measuring at least 35x25 are glued at an angle of 45°. This prevents cracks from forming in the corners of openings.
To strengthen the corners of the house, corner profiles with mesh are used.
Not filling the seams between the insulation
The result is the formation of cold bridges. To fill gaps up to 4 mm wide, use polyurethane foam for the facade.
Not using primer before coat decorative plaster
Some people mistakenly apply finishing decorative plaster directly to the mesh layer, abandoning the special (not cheap) primer. This leads to improper gluing of decorative plaster and the appearance of gaps gray from glue and the rough surface of the insulated facade. In addition, after a few years, such plaster cracks and falls off in pieces.
Mistakes when applying decorative plaster
Thin-film plasters can be performed after 3 days from the date of completion of the reinforcing layer.
The work must be organized so that the team works without interruptions on at least 2 or 3 levels of scaffolding. This prevents the appearance of uneven color on the facade due to its drying at different times.
In this article I will consider the issues of ventilation of the inter-wall space and the connection between this ventilation and insulation. In particular, I would like to understand why a ventilation gap is needed, how it differs from an air gap, what its functions are, and whether a gap in the wall can perform a thermal insulation function. This issue has become quite relevant lately and causes many misunderstandings and questions. Here I give my private expert opinion, based only on personal experience and on nothing else.
Denial of responsibility
Having already written the article and re-reading it again, I see that the processes occurring during the ventilation of the inter-wall space are much more complex and multifaceted than I described. But I decided to leave it like this, in a simplified version. Particularly meticulous citizens, please write comments. We will complicate the description as we work.
The essence of the problem (subject part)
Let's understand the subject matter and agree on terms, otherwise it may turn out that we are talking about one thing, but mean completely opposite things.
This is our main subject. The wall can be uniform, for example, brick, or wood, or foam concrete, or cast. But a wall can also consist of several layers. For example, the wall itself ( brickwork), a layer of insulation-thermal insulator, a layer of external finishing.
Air gap
This is the wall layer. Most often it is technological. It turns out by itself, and without it it is either impossible to build our wall, or it is very difficult to do it. As an example we can give this additional element walls as a leveling frame.
Let's assume we have a newly built wooden house. We want to finish him off. First of all, we apply the rule and make sure that the wall is curved. Moreover, if you look at the house from a distance, you see a quite decent house, but when you apply the rule to the wall, it becomes clear that the wall is horribly crooked. Well... there's nothing you can do about it! This happens with wooden houses. We level the wall with a frame. As a result, a space filled with air is formed between the wall and the external decoration. Otherwise, without a frame, it will not be possible to make a decent exterior decoration of our house - the corners will “disintegrate.” As a result, we get an air gap.
Let us remember this important feature of the term under consideration.
Ventilation gap
This is also a layer of the wall. It looks like an air gap, but it has a purpose. Specifically, it is designed for ventilation. In the context of this article, ventilation is a series of measures aimed at removing moisture from the wall and keeping it dry. Could this layer combine the technological properties of an air gap? Yes, maybe that’s what this article is being written about, in essence.
Physics of processes inside the wall Condensation
Why dry the wall? Is she getting wet or what? Yes, it gets wet. And you don't need to hose it down to get it wet. The temperature difference from the heat of the day to the coolness of the night is quite enough. The problem of getting the wall, all its layers, wet as a result of moisture condensation might be irrelevant in a frosty winter, but here the heating of our house comes into play. As a result of the fact that we heat our houses, warm air tends to leave the warm room and moisture condensation occurs again in the thickness of the wall. Thus, the relevance of drying the wall remains at any time of the year.
Convection
Please pay attention to what is on the site good article about the theory of condensation in walls
Warm air tends to rise and cold air tends to sink. And this is very unfortunate, since in our apartments and houses we live not on the ceiling, where warm air collects, but on the floor, where cold air collects. But I seem to have gotten distracted.
It is impossible to completely get rid of convection. And this is also very unfortunate.
But let's take a closer look useful question. How does convection in a wide gap differ from the same convection in a narrow gap? We have already understood that the air in the gap moves in two directions. On a warm surface it moves up, and on a cold surface it goes down. And this is where I want to ask a question. What happens in the middle of our gap? And the answer to this question is quite complicated. I believe that the layer of air directly at the surface moves as quickly as possible. It pulls along layers of air that are nearby. As far as I understand, this happens due to friction. But the friction in the air is quite weak, so the movement of neighboring layers is much less fast than the “wall” ones. But there is still a place where the air moving up comes into contact with the air moving down. Apparently in this place, where multidirectional flows meet, something like turbulence occurs. The lower the flow speed, the weaker the turbulence. If the gap is wide enough, these swirls may be completely absent or completely invisible.
But what if our gap is 20 or 30 mm? Then the turbulence can be stronger. These vortices will not only mix the flows, but also slow down each other. It seems that if you make an air gap, you should strive to make it thinner. Then two differently directed convection flows will interfere with each other. And that's what we need.
Let's look at some funny examples. First example
Let us have a wall with an air gap. The gap is blank. The air in this gap has no connection with the air outside the gap. On one side of the wall it is warm, on the other it is cold. Ultimately this means that internal sides in our gap they differ in temperature in the same way. What happens in the gap? The air in the gap rises along the warm surface. When it's cold it goes down. Since this is the same air, a cycle is formed. During this cycle, heat is actively transferred from one surface to another. And actively. This means that it is strong. Question. Does our air gap perform a useful function? Looks like no. It looks like it is actively cooling the walls for us. Is there anything useful in this air gap of ours? No. There doesn't seem to be anything useful in it. Basically and forever and ever.
Second example. 
Suppose we made holes at the top and bottom so that the air in the gap communicates with outside world. What has changed for us? And the fact is that now there seems to be no cycle. Either it is there, but there is also air leaking and venting. Now the air is heated from the warm surface and, perhaps partially, flies out (warm), and cold air from the street takes its place from below. Is it good or bad? Is it very different from the first example? At first glance it gets even worse. The heat goes outside.
I will note the following. Yes, now we are heating the atmosphere, but in the first example we were heating the casing. How much is the first option worse or better than the second? You know, I think these are approximately the same options in terms of their harmfulness. My intuition tells me this, so, just in case, I don’t insist that I’m right. But in this second example we got one useful feature. Now our gap has become an air ventilation gap, that is, we have added the function of removing moist air, and therefore drying the walls.
Is there convection in the ventilation gap or does the air move in one direction?
Of course have! In the same way, warm air moves up and cold air moves down. It's just not always the same air. And there is also harm from convection. Therefore, the ventilation gap, just like the air gap, does not need to be made wide. We don't need wind in the ventilation gap!
What's good about drying a wall?
Above, I called the process of heat transfer in the air gap active. By analogy, I will call the process of heat transfer inside the wall passive. Well, maybe this classification is not too strict, but the article is mine, and in it I have the right to such outrages. So here it is. A dry wall has a much lower thermal conductivity than a damp wall. As a result, heat will flow more slowly from inside warm room to the harmful air gap and being carried outside will also become less. Simply, convection will slow down, since the left surface of our gap will no longer be so warm. The physics of the increase in thermal conductivity of a damp wall is that vapor molecules transfer more energy when colliding with each other and with air molecules than just air molecules colliding with each other.
How does the wall ventilation process work?
Well, it's simple. Moisture appears on the surface of the wall. The air moves along the wall and carries away moisture from it. The faster the air moves, the faster the wall dries out if it is wet. It's simple. But it gets more interesting.
What wall ventilation rate do we need? This is one of the key questions of the article. By answering it, we will understand a lot about the principle of constructing ventilation gaps. Since we are not dealing with water, but with steam, and the latter is most often just warm air, we need to remove this warm air from the wall. But by removing warm air, we cool the wall. In order not to cool the wall, we need such ventilation, such a speed of air movement at which the steam would be removed, but a lot of heat would not be taken away from the wall. Unfortunately, I cannot say how many cubes per hour should pass along our wall. But I can imagine that it’s not a lot at all. A certain compromise is needed between the benefits of ventilation and the harm from heat removal.
Interim conclusions
The time has come to sum up some results, without which we would not want to move on.
There is nothing good about an air gap.
Yes indeed. As shown above, a simple air gap does not provide any useful function. This should mean it should be avoided. But I have always been kind to the phenomenon of an air gap. Why? As always, for a number of reasons. And, by the way, I can justify each one.
Firstly, the air gap is a technological phenomenon and it is simply impossible to do without it.
Secondly, if I can’t do it, then why should I unnecessarily intimidate honest citizens?
And thirdly, damage from the air gap does not rank first in the ranking of damage to thermal conductivity and construction mistakes.
But please remember the following to avoid future misunderstandings. An air gap can never, under any circumstances, serve to reduce the thermal conductivity of a wall. That is, the air gap cannot make the wall warmer.
And if you are going to make a gap, then you need to make it narrower, not wider. Then the convection currents will interfere with each other.
The ventilation gap has only one useful function.
This is true and it's a shame. But this single function is extremely, simply vitally important. Moreover, it is simply impossible to live without it. In addition, we will next consider options for reducing harm from air and ventilation gaps while maintaining the positive functions of the latter.
A ventilation gap, as opposed to an air gap, can improve the thermal conductivity of the wall. But not due to the fact that the air in it has low thermal conductivity, but due to the fact that the main wall or thermal insulation layer becomes drier.
How to reduce damage from air convection in the ventilation gap?
Obviously, to reduce convection means to prevent it. As we have already found out, we can prevent convection by colliding two convection currents. That is, make the ventilation gap very narrow. But we can also fill this gap with something that would not stop convection, but would significantly slow it down. What could it be?
Foam concrete or gas silicate? By the way, foam concrete and gas silicate are quite porous and I am ready to believe that there is weak convection in a block of these materials. On the other hand, our wall is high. It can be 3 or 7 meters or more in height. The greater the distance the air has to travel, the more porous the material we must have. Most likely, foam concrete and gas silicate are not suitable.
Moreover, the tree is not suitable, ceramic brick and so on.
Styrofoam? Not! Polystyrene foam is also not suitable. It is not too easily permeable to water vapor, especially if it needs to travel more than three meters.
Bulk materials? Like expanded clay? Here, by the way, is an interesting proposal. It could probably work, but expanded clay is too inconvenient to use. It gets dusty, wakes up and all that.
Low density wool? Yes. I think very low density cotton wool is the leader for our purposes. But cotton wool is not produced at all thin layer. You can find canvases and slabs at least 5 cm thick.
As practice shows, all these arguments are good and useful only in theoretical terms. IN real life you can do it much simpler and more prosaically, which I will write about in a pathetic manner in the next section.
The main result, or what, after all, should be done in practice?
- During construction personal home There is no need to specially create air and ventilation gaps. You won't achieve much benefit, but you can cause harm. If the construction technology allows you to do without a gap, don’t do it.
- If you can’t do without a gap, then you need to leave it. But you shouldn’t make it wider than circumstances and common sense require.
- If you have an air gap, is it worth expanding (converting) it to a ventilation gap? My advice: “Don’t worry about it and act according to the circumstances. If it seems like it would be better to do it, or you just want it, or this is a principled position, then make a ventilation one, but if not, leave the air one.”
- Never, under any circumstances, use materials that are less porous than the materials of the wall itself when constructing exterior decoration. This applies to roofing felt, penoplex and in some cases to polystyrene foam (expanded polystyrene) and also to polyurethane foam. Please note that if a thorough vapor barrier is installed on the inner surface of the walls, then failure to comply with this point will not cause harm other than cost overruns.
- If you are making a wall with external insulation, then use cotton wool and do not make any ventilation gaps. Everything will dry out wonderfully right through the cotton wool. But in this case, it is still necessary to provide air access to the ends of the insulation from below and above. Or just on top. This is necessary so that convection, although weak, exists.
- But what to do if the house is finished with waterproof material on the outside using technology? For example, a frame house with an outer layer of OSB? In this case, it is necessary to either provide air access into the space between the walls (bottom and top), or provide a vapor barrier inside the room. I like the last option much better.
- If a vapor barrier was provided when installing the interior decoration, is it worth making ventilation gaps? No. In this case, ventilation of the wall is unnecessary, because there is no access to moisture from the room. The ventilation gaps do not provide any additional thermal insulation. They just dry the wall and that's it.
- Wind protection. I believe that wind protection is not needed. The role of windbreak is performed remarkably well by itself. external finishing. Lining, siding, tiles and so on. Moreover, again, my personal opinion, the cracks in the lining do not contribute enough to the blowing out of heat to use wind protection. But this opinion is my own, it is quite controversial and I do not instruct on it. Again, wind protection manufacturers also “want to eat.” Of course, I have a substantiation for this opinion and I can give it for those interested. But in any case, we must remember that the wind cools the walls very much, and the wind is a very serious cause for concern for those who want to save on heating.
ATTENTION!!!
To this article
there is a comment
If there is no clarity, then read the answer to the question of a person for whom everything was also not clear and he asked me to return to the topic.
I hope that the above article answered many questions and brought clarity.
Dmitry Belkin
Article created 01/11/2013
Article edited 04/26/2013
Similar materials - selected by keywords
When insulating the walls of a wooden house, many make at least one of the four most insidious mistakes that lead to rapid rotting of the walls.
It is important to understand that the warm interior space of the house is always saturated with vapors. Steam is contained in the air exhaled by a person and is formed in large quantities in bathrooms and kitchens. Moreover, the higher the air temperature, the greater the amount of steam it can hold. As the temperature drops, the ability to hold moisture in the air decreases, and the excess falls out as condensation on colder surfaces. What will moisture replenishment lead to? wooden structures– it’s not difficult to guess. Therefore, I would like to identify four main mistakes that can lead to a sad result.
Insulating walls from the inside is highly undesirable, since the dew point will move inside the room, which will lead to moisture condensation in the cold wooden surface walls.
But if this is the only one affordable option insulation, then you must take care of the presence of a vapor barrier and two ventilation gaps.
Ideally, the wall “pie” should look like this:
- interior decoration;
- ventilation gap ~30 mm;
- high-quality vapor barrier;
- insulation;
- membrane (waterproofing);
- second ventilation gap;
- wooden wall.
It must be remembered that the thicker the insulation layer, the smaller the difference in external and internal temperatures will be required for the formation of condensation on wooden wall. And in order to ensure the necessary microclimate between the insulation and the wall, several holes are drilled into the bottom of the wall. ventilation holes(vents) with a diameter of 10 mm at a distance of approximately one meter from each other.
If the house is located in warm regions, and the temperature difference inside and outside the room does not exceed 30-35°C, then the second ventilation gap and membrane can theoretically be removed by placing the insulation directly on the wall. But to say for sure, you need to calculate the position of the dew point at different temperatures.
Using a vapor barrier for external insulation
Placing a vapor barrier on the outside of a wall is more serious mistake, especially if the walls inside the room are not protected by this same vapor barrier.
The timber absorbs moisture from the air well, and if it is waterproofed on one side, expect trouble.
The correct version of the “pie” for external insulation looks like this:
Interior finishing (9);
- vapor barrier (8);
- wooden wall (6);
- insulation (4);
- waterproofing (3);
- ventilation gap (2);
- external finishing (1).
Using insulation with low vapor permeability
Using insulation with low vapor permeability when insulating walls outside, such as extruded polystyrene foam boards, will be equivalent to placing a vapor barrier on the wall. Such material will prohibit moisture on a wooden wall and will contribute to rotting.
Insulation with equivalent or greater vapor permeability than wood is placed on wooden walls. Various mineral wool insulation and ecowool are perfect here.
No ventilation gap between the insulation and the exterior finish
Vapors that have penetrated into the insulation can be effectively removed from it only if there is a vapor-permeable ventilated surface, which is a moisture-proof membrane (waterproofing) with a ventilation gap. If the same siding is placed close to it, the escape of vapors will be greatly hampered, and moisture will condense either inside the insulation, or, even worse, on a wooden wall with all the ensuing consequences.
You may also be interested:
- 8 mistakes during construction frame houses(photo)
- The cheaper it is to heat a house (gas, wood, electricity, coal, diesel)
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Is a vapor barrier necessary when insulating a wooden house made of timber from the outside? What is the difference between a vapor barrier and c c d top and bottom
