Contents
If the attic remains non-residential, the air in the under-roof space serves as good thermal insulation (along with floor insulation). In the case of the attic, everything is completely different: here the thermal insulation is very close to the roofing material and the task is not only to insulate the attic, but also to create conditions so that the entire roofing system serves for a long time.
Let’s say right away that all the wood that is used in the construction of the roof must be treated with antiseptics. Indeed, everything: both battens and counter-battens, and rafters. All wooden parts. It is also necessary to make them less flammable. To do this, they are treated with flame retardants. All elements that are located on the side of the street are treated with compounds for outdoor work. Treat all wooden parts facing the inside of the room with impregnations for interior work. If you use the composition for outdoor use indoors, the specific smell will remain for several years. If on the contrary, the wood outside may suffer: the degree of protection is insufficient. So don’t skimp on this.
More. Before describing how to insulate a mansard roof with your own hands, it is worth recalling this: a ventilation system must be organized in the under-roof space. For this, special ventilation holes are arranged on the skate. Through them, the air from under the roofing material escapes, carrying away excess moisture. And it must fall under the roofing through the overhangs. There absolutely can not be done all hermetically. That’s where the air comes from. Only in this way will the condensate dry out in a timely manner and the roof will serve for a long time.
Proper attic insulation
In order for the attic floor to be warm in winter and cool in summer, there are no problems with high humidity, icicles do not freeze on the roof, it is necessary to properly insulate the roof. But in the case of a roof, insulation, vapor and waterproofing are a complex solution, and one without the other works very poorly, or does not work at all.
If the sloping roof is at the same time the walls of the attic floor, the pie will be as follows (from inside to outside):
- internal lining (drywall or lining);
- crate;
- vapor barrier;
- insulation (the thickness of the insulation depends on the region and the parameters of the insulation, for central Russia it is about 200 mm);
- superdiffusion membrane;
- ventzazor;
- crate;
- roof covering.
The photo shows the insulation of a broken mansard roof in a graphical version. Please note: a superdiffusion membrane is laid over the insulation (indicated in blue). Its purpose is to prevent condensate formed or precipitation seeping through the roofing from entering the insulation and removing the steam that nevertheless got into the mineral wool, ensuring its drying. Therefore, with a vapor permeability of 1500 g / m2. This layer is often called waterproofing (as it is, in fact, it is), only waterproofing is vapor-permeable.
Laying waterproofing
Ideally, it fits exactly as shown in the figure: wrapping the rafters and closely fitting on the insulation. Often, to save money, they roll it out over the rafters, but without pulling it, but making it sag by 3-5 cm. This option also works well: moisture gets to the surface, and then rolls down and out of the roof. Here is another important point: the membrane must go into the gutter. Then the moisture will be removed from the under-roof space.
A few more points on laying the membrane. It rolls across the rafters, starting from the bottom. The first row is launched into the gutter. The next one is rolled out with an overlap of 10-15 cm. And so on until the ridge. On the ridge, the membranes are cut off on both sides along the upper edge and fixed. A strip rolls along the ridge, descending from one and the other side of the roof. It turns out a coating through which water flows down to the gutter itself.
Vapor barrier and rules for its installation
It is worth talking separately about the vapor barrier. It must also be a membrane. Polyethylene or polypropylene film will not work: its characteristics are not the same. The vapor permeability of this layer (expressed in g/m2) should be minimal. Ideally, it is equal to zero. That is, this layer should not allow vapors to pass from the room into the insulation layer. When using mineral wool as insulation, this is very important: when wet, it loses more than half of its properties, and when it freezes in a wet state and then melts, it generally crumbles into dust.
Therefore, the vapor barrier film is also laid with the entry of one panel onto another. Moreover, these joints are glued with a special double-sided vapor-tight tape (it looks like sticky rubber). Ordinary painting or stationery will not work. They do not provide 100% vapor protection. In addition to the joints, all junctions are also glued: from below, from the sides, from above.
The vapor barrier is usually attached to the lags with stapler brackets or, as in the figure, with planks of the inner crate for mounting the skin. In this case, another ventilation gap is formed, which will dry the finish and the membrane. This clearance is desirable but not required. In principle, the lining can be mounted directly on top of the membrane.
Thermal insulation
The better to insulate a sloping roof – the question is complex and there is no unambiguous answer to it. Mineral wool is used, only hard, with a density of 30-50 kg / m3. Since the mansard roof usually has a large angle of inclination, soft materials can slip. It is for this reason that it is better to take plates. Although in this case it will be necessary to adjust the pitch of the rafters to the dimensions of the insulation: it should be 10-15 mm less than the width of the plate so that the material becomes “spread” between the beams and holds well.
It is necessary to lay thermal insulation in such a way that there are as few cold bridges as possible. For central Russia, usually 200-250 mm of mineral wool is required. These are several layers of mats. When laying between the rafters, the slabs are positioned so that the seams of one row overlap the next. The width of the insulation, as already mentioned, should be slightly wider than the distance between the rafters. Then the plate becomes dense, excluding the presence of cracks. If the width is more/less, you have to cut the material. At the same time, the chance to get a smooth edge is small and there are many residues.
If the dimensions of the rafter do not allow laying the entire insulation, planks of the required thickness are stuffed across from the side of the room. Between them lay the remnants of insulation. From above, a vapor barrier is already attached to it and, if necessary, a crate for finishing. This option is even better: cold bridges are completely excluded, blocking even the rafters. This method requires a little more installation costs, but it will definitely be warmer in the attic, which will reduce heating costs.
How to insulate a mansard roof: the order of work
The device of the attic floor is good because it allows you to stretch the end of construction. It is immediately necessary to lay and fix the superdiffusion membrane on the rafters, the crate and roofing material on it. And attic insulation can be done from the inside after a while.
But pay attention: the waterproofing layer must be mounted together with the roofing. This is the main mistake of many developers: they do not lay this membrane. As a result, either it is necessary to remove the roof and lay it, or to invent systems to correct this shortcoming. The whole problem is that in this case there is no cheap solution that guarantees the normal state of the materials.
We warm outside
If you do everything at once, the order of work is as follows:
- from the side of the room, a crate is stuffed across the rafters – thermal insulation will lie on it, instead of a crate, a cord or galvanized wire is sometimes attached;
- heat-insulating material is laid on it from the side of the roof (according to all the rules, shifting the seams, making sure that there are no gaps);
- a superdiffusion membrane is rolled over the thermal insulation;
- crate is stuffed;
- roofing is laid;
- from the side of the room, a vapor barrier is fixed and glued;
- with or without crate mount trim.
Insulation of the mansard roof from the outside: it is not difficult to work, the thermal insulation is laid on the crate lined from below
With this option, it is not difficult to work with a heater: it is easy to lay it, it relies on a crate (laces).
Insulation from the inside
This option allows you to move the interior decoration for the required period (useful if there is a shortage of funds). After installing the truss system, here’s what you need to do:
- roll out and fix the waterproofing;
- stuff the crate (if necessary, a counter-crate);
- install roofing material.
For the first stage, this is all the necessary work. After the opportunity to continue, you will need to insulate the mansard roof from the inside. It will no longer be so convenient to work: you will have to make a building envelope that will not allow you to push the insulation higher than necessary. The cotton wool itself will have to be fixed in some way: it strives to fall on the head. The order of work is as follows:
- between the lags in increments of 40-50 cm, stuff the strips that will hold the thermal insulation, providing the required ventilation gap;
- thermal insulation of the required thickness is laid and fixed (the rules remain the same);
- a crate is nailed to hold the layers of insulation;
- a vapor barrier membrane is laid and glued;
- the crate and finishing material is mounted.
If you use plates, then it is also easy to insulate the attic from the inside.
A few notes on how you can lay the heat-insulating material. If these are high-density mineral wool mats and their width is a little more than the step between the joists, everything is relatively simple: they themselves hold up well.
If rolled mineral wool is laid, everything is more complicated. Making the insulation of the mansard roof from the inside, it is laid from the bottom up. Take a string, a construction stapler. Roll out the cotton wool, press it against the planks, fasten a piece of lace with staples, drawing the letter Z. This is how you fix the first layer, followed by the second and all subsequent ones.
In general, if you want the mansard roof to be warm, it is better to use mineral wool mats of the required density of 30-50 kg / m3. They are tough enough to hold their shape well. Softer rolled materials on vertical surfaces or with a large slope are caked, settling down, the thermal insulation of the mansard roof deteriorates.
What is the best way to insulate a mansard roof
As mentioned above, the most popular material for insulating a mansard roof is mineral wool. It is good, but not at all ideal: it is afraid of moisture. That is why it requires such careful protection from all sides so that it retains its properties.
Styrofoam (expanded polystyrene)
Sheathe the roof with polystyrene foam or extruded polystyrene foam – EPS. Polyfoam (grades PSB-S-25, PSB-S-35) has good characteristics, but when burned, it emits harmful substances, although there are self-extinguishing grades (with special additives). Here they are better for roof insulation for roof insulation.
The main advantage of polyfoam: low price. It is mounted simply: it is placed between the rafters, all joints are sealed with mounting foam. It is convenient to insulate the attic from the inside with foam plastic: order the plates of the right size – 10-15 mm more than the gap between the rafters – and put them tightly. Due to the elasticity, they hold very well.
From the side of the roof, a ventilation gap is also left and waterproofing is laid. But it protects more a wooden structure, since polystyrene foam is not afraid of moisture, it practically does not absorb it itself, it does not conduct steam. This is where the main drawback lies. Since the material does not let the vapor through, a good ventilation system is needed in the attic, and this is an additional cost.
XPS has the best characteristics: under equal conditions, its thickness is two times less than mineral wool of the specified density and one and a half times less than that of polystyrene. It also has a system of locks, which reduces the risk of cracks, through which heat will fly away. Another plus: mice and insects do not like extruded polystyrene foam, fungi and mold do not multiply on it. What limits its use: a solid price. You also need a ventilation system.
EPPS brands – Ekstrol, STEREKS, PENOPLEX, URSA XPS, Technoplex, PRIMAPLEX (PRIMAPLEX), Styrofoam (Styrofoam), KINPLAST (KINPLAST), Teploizolit, GREENPLEX (GREENPLEX). While the technology is the same, there are some differences in performance, so compare when choosing.
Not so long ago, a new type of insulation appeared: expanded polystyrene foam. It is applied in liquid form to the surface, reacting with air, increases in size many times, filling all the cracks and forming a monolithic layer. This is perhaps the only way today to correct the situation and insulate the attic with high quality, if during the installation of the roofing they forgot to lay a layer of waterproofing.
Ecowool
This insulation has good characteristics (thermal conductivity coefficient 0,036-0,040 W / m² ° C), but a special application technology. It is necessary to organize a closed cavity into which the composition is poured. In the case of a mansard roof, the side parts are rafters, sheet material (fiberboard, GVL, plywood, etc.) is nailed to them from below and from above.
A feeding sleeve is launched into the formed cavity, from which loosened cotton wool comes out under pressure. It fills all the cavities, forming a single layer of insulation.
The main advantage of ecowool compared to all the heaters described above is that it conducts steam. It can absorb moisture up to 20% of the volume, and then give it away. That is, there is no need to organize a vapor barrier: humidity is regulated in a natural way, as is the case with wood. The ventilation gap between the roof and the insulation should be all the same, as well as the properly organized movement of air masses in it.