With the arrival of a new year, it is time to evaluate those roofing issues that have recently changed, as well as those that reflect long-term stability and durability.
The September 2013 issue of Interface Magazine, the journal of RCI, noted many transitions taking place in the building envelope.
The 2012 International Building Code (IBC), as cited in theInterface article, provides climate zone maps of the U.S. that list the required R-values when the thermal insulation in a commercial roof system is:
- Above the roof deck
- Beneath the deck in a metal roof system
- On the floor of an attic
The December issue of Roofing Contractor suggests a systematic approach to insulating new structures and retrofitting existing roof inventory.
Looking backwards, the oil embargo of 1972-1973 highlighted the sudden demand for energy conservation. A typical roof structure at that time was one with perhaps 3/4 to 1 inch of roof insulation, generally wood fiber, perlite, or glass fiber, with R-values around 3 per inch of thickness.
On the West Coast, fiberglass underdeck batts with an R-value of 7 might be used. Hybrid systems used perlite or glass fiber as a fire barrier, laminated to the desired thickness of newly introduced polyurethane foam. Today, we have reintroduced such systems using cover boards, usually of gypsum board.Cellular foams of polystyrene and urethane/ polyisocyanurate now meet the demands of greatly increased R-values. Extruded polystyrene is generally quoted at an R-value of 5.0 per inch, while isoboards are quoted at 5.6 (recently downgraded from as much as 7.2 per inch). A roof in climate zone 5, for example, now requires an R of 25, or 4.46 inches of thickness for isoboards. (Note that wood nailers need to meet this required thickness, as do wall scuppers, equipment curbs, and other components.)
The best recommendation is to take exceptional care of what you already have. However, if replacement is ultimately unavoidable, be sure to know the facts and select a reputable installer that can not only meet the code requirements, but the specific needs of your building as well.