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The building envelope is the combination of the foundation, wall, and roof assemblies all working
together to provide a comfortable and safe environment in a building. It also preserves the
structural integrity of the building.
The building envelope works in conjunction with the heating,
cooling, and ventilation systems to perform several major functions:
- Controls the comfort level inside by managing temperature and relative humidity.
- Reduces heating and air conditioning cost.
- Prevents problems such as pipe freeze-ups.
- Prevents insect and vermin infestation of the building.
- Prevents condensation inside of the building’s foundation, walls, and roof assemblies.
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If you build a wall to code with R-19 fiberglass in 2x6 framing and OSB sheathing, the dew point
will fall inside the wall cavity—period
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Several more expensive materials are gaining attention for what else they can offer—notably, help
with air infiltration and condensation inside walls, which are major sources of callbacks and
litigation.
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Insulation, is no longer just a matter of R-value per dollar. Traditional insulations such as
Fiberglass and cellulose are not very effective against the radiant heat loss in a home. Warm
air inside the house and cold air outsite can cause the dew point to occur in the walls. When
the dew point occurs in the walls:
- Moist air from inside condensing on the inside of wall cavities, which can lead to the wood rotting or metal rusting.
- Condensation on the inside of wall cavities that can lead to mold and mildew growth, which can be unhealthy for building occupants.
- An increase in the level of interior pollutants such as volatile organic compounds from cleaning products.
- An increase in the concentration of soil gas like Radon in basements, crawl spaces, and slabs.
References
- Bynum, Richard, 2001. Insulation Handbook, McGraw-Hill, New York, NY
- Lstiburek, Joseph and John Carmody, 1993. Moisture Control Handbook, Van Nostrand Reinhold, New York, NY
- Lstiburek, Joseph, 1998. Builders Guide: Cold Climates, Building Science Corporation, Westford, MA
Related Links
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