Literature Review on Building Envelope, Heating and ... - Beeshive.org

of Alaska museum where RH was 45%. Adkins suggested 30% RH in buildings in
Fairbanks was reasonable and achievable in residential buildings. In commercial
buildings, 30% RH could be achieved by separating the construction process of the
vapour and insulation from interference by the structure, electrical, mechanical, and
finish materials.
Moisture Control: Northern Regions
Three types of barriers are needed in building envelopes in the north (CMHC, 1994-1):
• a wind or weather barrier on the outside of the envelope to protect the envelope from
blowing snow and rain;
• an air barrier system to prevent exfiltration of indoor air through the envelope; and
• a vapour barrier, on the warm side of the envelope, to prevent water vapour from
entering the envelope.
One material may serve as an air and vapour barrier provided it is located on the warm
side of the envelope.
Impact of Improper Selection and Placement of the Vapour Barrier, Arctic
Carlson (1996) demonstrated how improper selection and placement of the insulation, the
vapour barrier, and the lack of venting of wall assemblies could lead to building envelope
deterioration due to condensation that usually becomes apparent five to ten years later.
Moisture diffusion through the inner layer of the building envelope might condense near
impermeable outer layers and freeze as the temperature drops below the dew point and
freezing. Moisture accumulation and frost buildup will be much greater in northern
climates, such as Alaska and Minnesota.
The examples included a retrofit of an impermeable exterior insulated and finish system
(EIFS), which was applied on the exterior of an insulated wall in a building in Fairbanks,
Alaska. A polyethylene vapour barrier was placed on the warm side next to the interior
gypsum board, but because of imperfections, water vapour diffused into the wall,
condensed, and froze near the inner face of the EIFS panel. As a result, the panel’s
fasteners corroded and the frost buildup caused some panels to protrude from the wall.
Carlson attributed this damage to a lack of venting of the EIFS panels. Venting would
allow excess moisture to drain or evaporate.
Carlson (1996) also presented a spreadsheet tool to assist designers and builders in the
selection and placement of the vapour barrier, insulation, and venting in the building
envelope assembly. The spreadsheet calculates dew point temperatures in insulated
building envelope assemblies. As an example, Carlson used the spreadsheet to investigate
moisture deterioration of a Fairbanks, Alaska, building. Carlson made the following
recommendations.
• A dew point analysis should be conducted for each building envelope assembly based
on local climate conditions. The calculations are particularly important for EIFS and
other insulated assemblies retrofitted over insulated steel or wood framing.
PERD-079: Task 2 - <strong>Literature</strong> <strong>Review</strong> 5