House insulation with polystyrene foam (expanded polystyrene)

Recommendation points

• What house can be insulated with expanded polystyrene
• Which expanded polystyrene is suitable for wall insulation
• Required insulation thickness
• General technical requirements
• Subtleties of installation

It would seem that the technique of insulation with polystyrene has long been studied and worked out. But still, there are often projects of houses, in the implementation of which serious mistakes were made, primarily in terms of thermal protection. The nuances that the portal will tell you about are true for any foam materials.

What house can be insulated with expanded polystyrene

Extruded foams are porous materials with a closed cell shape. They do not allow gases and water vapor to pass through, which introduces a number of restrictions regarding the properties of the enclosing structures and the organization of the indoor climate.

If the walls have non-zero gas permeability, water vapor falling on the inner surface of the heat protection belt turns out to be in the zone of a sharp temperature drop and condenses between the carrier layer and the insulation. Water is formed directly in the glue line, causing its erosion and loss of strength properties. What is worse – moisture is trapped in the pores of the wall material, which provokes the development of fungus and mold.

It is necessary to take into account not only the properties of building materials, but the entire supporting structure as a whole. So, a wooden beam does not allow steam to pass through, but at the same time the frame is permeable to gases due to the large number of slots.

Another example is a frame house, the supporting structure of which does not retain water vapor. But at the same time, the mineral filler of the walls is always protected from moisture by a vapor barrier or superdiffusion membrane..

From the point of view of physical and mechanical properties, stone buildings made of bricks, aerated concrete or other masonry materials are most suitable for insulating PPP. At the same time, there are successful examples of additional insulation of frame houses, which are subject to seasonal deformations to a greater extent, but at the same time, the insulation and facade decoration remain intact for decades..

Here’s what to consider when developing a home construction project:

• Polyfoam is used where high stability of the supporting structure is ensured (correct foundation, necessarily concrete, seismic belt, masonry reinforcement, internal spacer walls).
• Any modern thermal protection system implies a mandatory vapor barrier on the inside.
• The rule arising from the previous one: since the walls do not provide air exchange with the external environment, the ventilation system must be properly organized in the house.

Which expanded polystyrene is suitable for wall insulation

There are two types of foam. White, consisting of granules (glued balls), is made by pressing and is not suitable for external wall insulation. This material is capable of accumulating moisture, which reduces its thermal insulation properties. Polyfoam of the PSB brand is used only for warming foundations, blind areas or heated screed.

The second type of expanded polystyrene is marked with EPS and is made by extruding the foam mass from the matrix. In this case, a hardened crust forms on the surface, and the material itself is essentially an insulator not only for heat, but also for liquid and gaseous media..

External wall insulation with expanded polystyrene is always carried out within the framework of the so-called wet facade. This system of heat-shielding lining is quite demanding in terms of technology and quality of materials. However, there is nothing difficult in observing these rules: leading manufacturers of insulation products, as well as glue and plaster mixtures, offer not only an exhaustive material base, but also technical albums and manuals to it. Their careful study will allow even a non-professional to independently equip a good and durable wet facade..

Required insulation thickness

A number of regulatory documents and construction manuals are devoted to the design of thermal protection of buildings. However, when insulating a private house, you can use a simplified scheme, because even with an excessively high resistance to heat transfer, the overrun of the insulation is relatively low.

To understand the purposes of heat engineering calculation, it will not be superfluous to familiarize yourself with SNiP 23–20–2003. This is the main standard, which establishes sufficient values ​​for the thermal conductivity of the enclosing structures for different types of buildings. But sufficient does not mean optimal, the current standards do not meet modern requirements for energy efficiency of buildings.

The foam’s resistance to heat transfer is so high that structural wall materials such as concrete and solid bricks are often not considered when calculating the overall thermal conductivity. Under any conditions, a 180–200 mm EPS sheath will be sufficient to bring the building’s energy balance to zero. This means that its own heat generation (from people, hot water supply and household appliances) will be enough to maintain a comfortable temperature.

However, 20 cm of foam is a lot. Difficulties arise both with the acquisition and delivery of such a large amount of insulation, and with its installation. Therefore, designers of private houses often proceed from such conditions that the temperature of the inner surface of the wall is no more than 4–5 ° C lower than that of room air. These data can be entered into an online calculator for calculating heat loss and moisture accumulation, the output will be approximately the following ratio of brick thickness and insulation:

• up to 250 mm – 45 mm;
• up to 400 mm – 40 mm;
• up to 640 mm – 30 mm.

General technical requirements

Thermal protection device regulation may differ from one technical manual to another. Nevertheless, there are a number of general rules that remain unchanged for all installation instructions:

1. PPS insulation is always located on the outside of the walls. The only exception to this rule is when the insulation is located in the thickness of the wall as the hollow two-row (well) masonry is being erected. The reason for this is simple: thermal insulation of a heated and inhabited building from the inside reduces the thermal inertia of building structures to zero..
2. Expanded polystyrene has mechanical and adhesive fastening. The latter is the main one, however, disc dowels are required: they ensure reliable pressing of the slab to the base for the period of setting and shrinkage of the adhesive mixture.
3. The glue is applied to the board in large lumps at at least five points (in the center and in the corners), before that, the EPSP surface is wiped with an adhesive mixture to improve adhesion to the extruded layer. Bonding the joints between the boards is strictly required.
4. It is unacceptable to level the unevenness of the wall with insulation plates. A rough plaster layer is pre-applied with tolerances of up to 5 mm / m in any direction and up to 20 mm over the entire area of ​​the facade. Correction of the thickness of the glue line is used only to deduce the ideal plane of the front plaster layer.
5. The insulation is covered with a base reinforcing layer immediately after the glue dries, that is, the next day. Even a short stay of the EPSP in the open air is fraught with material destruction and a decrease in surface adhesion..

Compliance with these five basic rules is quite enough for the arrangement of reliable thermal protection. But it will not be superfluous to listen to other recommendations of the management, which may concern:

• the choice of density and grade of foam, depending on the thickness and operating conditions;
• selection of an adhesive mixture for a specific type of board;
• methods of surface preparation before the device of each subsequent layer;
• the procedure for laying and bandaging insulation;
• selection of the basic plaster mixture that is optimal for the used EPSP brand;
• holding time for glue and plaster layers to dry.

Subtleties of installation

As it was said, EPS is used mainly for the construction of a “wet” plaster facade, which consists of:

1. A layer of leveling cement plaster.
2. EPS boards fixed with special glue.
3. Base reinforcing layer, reinforced with a facade fiberglass mesh.
4. A decorative finishing layer such as paint or textured plaster.

If the planned structure of your facade differs from the one described, for example, it is planned to install a curtain cladding, it is better to refuse from expanded polystyrene in favor of another insulation system. If you understand the purpose and purpose of the material in question, feel free to get to work. Here are some tips to make installation easier and avoid mistakes:

• It is better to cut the plates with a special hacksaw. When using a hot knife, the ends melt, which impairs adhesion.
• After fixing the next plate, the protruding glue must be carefully rubbed with a spatula along the joints.
• Do not dismiss the primer: even the surface of the EPSP under certain conditions may require processing.
• In buildings higher than one floor above the openings, it is necessary to arrange fire cut-off from non-combustible mineral wool.
• The belt of external thermal protection must be continuous, including window and door slopes.
• The upper edge of the facade insulation cake should be protected by a roof cornice or a metal ebb strip.

Insulation of the facade with expanded polystyrene is a technology that does not tolerate innovation. Only following the installation regulations will ensure a really high service life and avoid damage to the facade finish during operation.