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The thermal resistance of the building envelope depends on thermal insulation and design solutions. In practice, however, workmanship may be just as important in the total thermal performance. In the building envelope, certain areas are more susceptible to deficiencies in workmanship than others. This fact should be considered in the design stage.
An ideally installed thermal insulation in a structure will have a well-known thermal resistance. Deviations from this situation will increase the U value. The influence is most important on walls and roofs with low U values, where even small deficiencies may seriously increase the heat loss.
The wind and pressure situation around a building and the air permeability of the structure may lead to air movements in the envelope. This may increase the heat loss. The importance of proper installation of wind protection in an insulated crossbar wall is shown. The increase in U value, especially in combination with deficiencies in the thermal insulation installation, is given. Airtightness of a structure is usually accomplished with a vapor barrier and specially designed joints between different building elements. Large air flows through a wall usually indicate cracks or openings in the vapor barrier and the inside. The increase in heat loss resulting from such flaws is shown. The influence on a building envelope with high thermal resistance is very large.
The results and discussions are related to building envelopes with high thermal resistance and low heat losses. This situation is typical of today's building design in Scandinavia.
thermal insulation, building envelope, workmanship, wind protection, airtightness
Professor, Swedish National Testing Institute, Borås,