From a thermal insulation point of view, these products added an R-value of about 3 per inch of thickness.Īfter the oil embargo of 1973-1974, the price of energy surged, making thermal insulation an important design consideration. Wood fiber, perlite board, and glass fiber board were used. To span the ribs of a steel deck, a leveling course of ¾ inch to 1 inch of roof insulation was used. After the war, steel, plywood, OSB, gypsum, insulating concrete, and other lightweight roof decks came into vogue. Because of the thermal mass and relatively low cost of energy, these buildings frequently did not use any thermal insulation at all. Prior to World War II, many buildings had either concrete or heavy timber roof decks.
ASHRAE 90.1 ROOF INSULATION REQUIREMENTS CODE
If the proposed changes above are adopted by ASHRAE and work their way into the International Building Code (IBC), the required minimum thickness of thermal insulation for each climate zone would look more like this:
ASHRAE 90.1 ROOF INSULATION REQUIREMENTS MANUAL
The Manual of Low Slope Roofing offers these R-values per inch of thickness for several common roofing materials: Note that different resources may provide different values. Published resistances (R-values) for construction materials can be found in the ASHRAE Handbook of Fundamentals and in material manufacturers’ literature. Metal Roofs (liner below purlins or uncompressed, unfaced insulation draped between purlins) Not all proposed changes are accepted, however, so stay tuned.ĪSHRAE’S Proposed New Insulation Requirements The proposed changes would require progressively greater amounts of thermal insulation in each zone (see below). For low-slope commercial roof systems, roofs in Zone 1 (the warmest climate) have required a minimum R-value of 15, and the remaining seven zones call for R=20. energy codes.įor the U.S., ASHRAE has prescribed eight climate zones.
BUILDINGS readers are probably aware of the recent changes to ASHRAE’s 90.1-2010 standard, which has long served as the model for U.S.