Frame House Walls: The Right Insulation Cake

2023 Author: Douglas Hoggarth | [email protected]. Last modified: 2023-05-24 11:23

• Carrying system of the frame building
• Insulation materials
• Thermal insulation protection
• Waterproofing of enclosing structures
• Preparation for finishing

Carrying system of the frame building

The correctness of the thermal protection device for a frame building is determined by each of the stages of construction, starting with the foundation. How competently the supporting system will be fixed to the base and what configuration it can have at the same time will play a decisive role for effective insulation, wind and sound protection.

The basic system of the frame wall device consists of vertically placed planks with an aspect ratio of the order of 3-5: 1. The thicker their cross-section, the better they conduct heat, the less - the more often the step of their installation should be. In addition, there may be a need for additional links. In particular, it is practiced to add diagonal spacers and ties between individual panels to the frame.

The quality of heat protection can be assessed by the total area of wooden elements in the longitudinal section of the wall. It is believed that the wood content of the thermal barrier should not exceed 18–20% of the total wall area. If necessary, you can reduce the wood content by developing your own frame structure, oriented to the shape of the building and its operating conditions.

The material for the frame is only high quality sawn timber of very low moisture content - no more than 11–12%. With an increase in humidity of only 3%, the thermal conductivity of the tree doubles. You should also choose the so-called core board, which has a predominant direction of fibers across the heat transfer path - the thermal conductivity of the racks, with their correct orientation, can be reduced by up to 2 times, depending on the type of wood.

Of the materials, calibrated timber is also widely used, which, although it has an average thermal conductivity due to the opposite direction of the fibers, can be used in smaller quantities due to its higher strength and stability. The situation is similar with hard wood species. Although they are denser and better conduct heat, sometimes reducing cold bridges is much more beneficial.

In the construction of passive houses, the frame is sometimes made multi-row: the internal subsystem is supplemented with crossbeams, to which the racks of the outer crate are attached. In this case, the cross-section of the cold bridges decreases several times and is approximately equal to the total area of contact of the two rows. This greatly facilitates the calculation of the thickness of the insulation, however, at least 2/3 of its total volume should fall on the outer layer of insulation.

Insulation materials

With the correct design of the frame, there comes a time when the presence of cold bridges can be neglected, for safety reasons only increasing the layer of insulation by 5-10%. However, how to determine if the thickness and thermal resistance will be sufficient to reduce heat loss to the required values?

A building is considered to be energy efficient if it loses no more than 100 kWh of thermal energy per square meter of total area in one year. Sometimes the total heat loss is determined by the maximum possible power of the heating equipment. Knowing the height of the enclosing walls and the length of the perimeter, it is enough to simply calculate the total area of the enclosing surfaces, divide them by type and calculate what is the share of the walls in heat exchange with the outdoor environment. Considering that the heating period is at least 180 days, it is easy to determine what value the specific thermal conductivity of the walls should be limited to in order to maintain the initial heat balance.

To select the required thickness of the insulation, take into account its thermal conductivity and temperature difference, which depends on the internal climatic regime and the mark of the thermometer in the coldest five-day period. It should also be borne in mind that the thermal conductivity of the insulation may increase or change over time during the year. If the calculation of heat loss was carried out not based on the maximum heating power, the temperature difference can be determined by the average temperature mark in January-February.

Thermal insulation protection

Some heaters require protection from getting wet, blown out or, for example, from direct sunlight. Some of these tasks can be assigned to the finishing layer, but the main protection is provided by special membrane materials.

One of the most commonly used heaters in the Canadian frame - stone wool - tends to dramatically reduce the resistance to heat transfer when wet. The source of moisture can be precipitation or condensation of water vapor. In the first case, special synthetic sackcloths are used, which allow air and water vapor to pass through, but retain water droplets.

The penetration of steam from the inside cannot be completely limited, because the building must carry out natural gas exchange with the environment. However, you can limit the amount of water vapor to such values, when it will not be enough to raise the relative humidity in the cooled indoor air to 85–90%. Usually, such a calculation is carried out for the dividing point of the rows of the frame or the supporting system with external insulation. However, the same method can also be used to calculate the dew point displacement over a year inside homogeneous walls.

Waterproofing of enclosing structures

Some types of materials for insulation have a closed cell structure and therefore do not absorb water at all. In this case, the calculated dew point displacement range is placed entirely in a layer of such insulation, because moisture cannot condense there, simply due to the lack of water vapor.

However, special care should be taken with this approach. In particular, for single-row frames, an additional calculation of the dew point displacement in the cold bridges is required, because the main way for steam leakage will remain the gaps between the frame and the insulation.

The formation of moisture on frame elements can be harmful not only in the long term. A sharp change in the moisture content of wood activates the warping processes, due to which, if the rigidity of the supporting structure is insufficient, the finish may be damaged or additional heat outflow paths may open.

It is quite easy to isolate the frame from direct moisture penetration. Chamber-dried wood, treated with an antiseptic and water-repellent impregnation, can be deafly isolated from the external environment for many decades, which will only increase its durability. In addition to the coating waterproofing, the frame can be covered with several layers of thin polystyrene or vinyl acetate packaging film.

Preparation for finishing

After installation and protection of the insulation, it is the turn to equip the supporting subsystem for the ventilated cladding or the plane for finishing with a wet facade. In the latter case, the wind and water protection of the insulation can be provided with a layer of plaster finish and / or paint.

Installation in both cases takes place according to different schemes. To ensure the necessary strength of the crate for the installation of panel materials, the step of installing the frame racks is chosen in advance quite often. After temporarily fixing the waterproof membrane with staples to the frame ribs, it is knocked out with spacer slats about 25-30 mm thick. In this case, space is provided for the drainage of water that has got inside and ventilation. If desired, the joining of the rails can be sealed with fresh oil paint or mastic.

Wall cake of a frame house: 1 - OSB inner lining; 2 - vapor barrier; 3 - insulation; 4 - wooden frame; 5 - superdiffusion membrane; 6 - counter lattice; 7 - facade decoration (siding, lining, block house)

When constructing a continuous crate for plastering, sheet materials are used, which serve as an excellent vapor barrier. A high concentration of moisture can provoke condensation of drops, for the removal of which a vent is provided between the waterproofing and the sheets. The sheets, in turn, exclude the blowing of the insulation.

Plastering of the walls of a frame house: 1 - OSB inner lining; 2 - vapor barrier; 3 - wooden frame; 4 - insulation; 5 - superdiffusion membrane; 6 - counter lattice; 7 - OSB outer skin; 8 - basic plaster; 9 - plaster mesh; 10 - decorative plaster

In some cases, the outrigger cladding system is mounted over sheet materials. This decision can be made due to the high dew point offset range. The possible formation of condensation in the ventilated layer does not promise any particular problems when using moisture-resistant sheets. However, in this case, the abutment to the base and the cornice has a more complex structure.