In areas of snow and cold, properly designed insulation is vital to the success of heated buildings. Roof insulation should be a minimum of R38 and wall insulation should be a minimum of R19. All insulation should be installed with a sealed vapor retarder on the warm side of the insulation with no penetrations, punctures or unsealed laps. Roof and wall vapor retarders must be fully integrated with each other. Electrical fixtures must not penetrate vapor retarder envelopes. Additional insulation not only increases thermal efficiency but also, if properly detailed, may improve the character of snow and ice formation on the roofs.
Insulation and vapor retarders must be properly detailed around openings in exterior walls and roofs. Windows with thermal breaks must be used to prevent condensation on jambs and sills. Super insulated roofs may be considered in place of cold roofs or attics. A super insulated roof is normally double the "R" value of a normal snow country roof and may need special structural connections, in a manner similar to cold roofs. Heat leaks through walls or roofs can create serious snow country hazards.
Choosing the appropriate material for a sloping roof in snow and cold country is an extremely important decision. The essential question is whether to encourage the snow to slide off the roof or to remain on it.
Slippery roofing such as metal, glass, slate, and some synthetic or metal shingles will allow the snow to slide or avalanche easily. In these cases, the falling snow must not create a hazard by dropping onto lower roofs, entries, walkways, balconies, parked cars, or people. It must fall into an area designed for this event, where the snow dump can be easily removed or simply allowed to remain throughout the winter. Also, sliding snow must not damage or shear off roof protrusions such as chimneys, skylights, or vents (Figure 18). Simple roof geometry is most important with slippery warm roofs.
