Construction document phase:
∞ Include the air barrier and the vapour retarder (when required) in the drawings;
∞ Identify specific components of the code-required air barrier system in the drawings;
∞ Include specification sections specific to the project, system, and material; and
∞ Provide details of the vapour retarder (when required), insulation, air barrier system, and weather-resistive barrier transitions (e.g. roof-to-wall) to ensure continuity and avoid the “by others” conundrum.
Bidding phase:
∞ Understand the risks of value engineering and life cycle cost implications (initial versus long-term costs); and
∞ Clearly communicate why components of the design are critical for long-term building performance and energy efficiency.
Construction administration phase:
∞ Review project submittals to ensure the specified products and systems are properly incorporated into the project and alternates are not substituted inappropriately.
Partnering with experts
The most successful buildings will not only meet the architect’s esthetic vision, but they will also be well-functioning for the occupant, as well as long-lasting, durable, and energy efficient. Building enclosure consultants who specialize in building science and energy modelling may be a valuable addition to a project team tasked with navigating the gap that sometimes exists between design and science.
It is also important, during the design and specification process, to work closely with product manufacturers that have experts on staff who understand building and roofing science, to ensure the correct products are used, and systems as designed will provide the expected performance to help lower an architect’s risk.
Author
James R. Kirby, AIA, is a GAF building and roofing science architect. Kirby has a master’s degree in architecture—structures option, and is a licensed architect. He has 30 years of experience in the roofing industry covering low-slope, steep-slope, metal, SPF, vegetative, and rooftop photovoltaics. He understands the effects of heat, air, and moisture on a roof system. Kirby presents building and roofing science information to architects, consultants, and building owners, and he writes articles and blogs for building owners, facility managers, and the roofing industry at large. Kirby is a member of AIA, ASTM, ICC, IIBEC, NRCA, and WSRCA.
This is a great explanation of important building science concepts that every roof designer needs to know!
Construction Canada received the following Letter to the Editor:
Dear Editor,
The article was very interesting and informative. Could the author comment on the affect this type of roof energy design has on the design roof snow load? The reason I ask is research in the United States indicates the roof load is significantly higher than for roofs retrofitted with R-30 insulation than older buildings. It has been observed that freezer buildings have significantly greater depths of snow on roofs than on the ground. I have also seen the same condition in my work in Canada. The commonly accepted explanation is the surface of the roofs are cooler than the ground and snow does not melt as normally expected. Up to this time, the ratio between ground to roof snow loads is based on extensive field studies done in the 1960s, so the reduction of snow depth on the roof is based on how roofs were insulated during this period. A discussion of increased snow loads on building roofs is well presented in the article “Snow Thermal Factors for Structural Renovations” in Structure Magazine (https://issuu.com/structuremag/docs/structure-jun19-zmag/24). The latest version of ASCE-7-22 has incorporated these factors. Also, for low sloped roofs, structural engineers are now required to calculate the roof deflections when checking for ponding of rain. With more snow on roofs, the roof deflects more which encourages ponding of rain during spring melting. Care needs to be taken to improve drainage off roofs to ensure ponding is less likely.
David P. Thompson, M.Sc., P.Eng.
Principal
KTA Structural Engineers