Since the late 1990’s when building designers and engineers began dispelling theories that newer buildings were air tight, there has been a concerted effort in the United States to develop building air tightness standards which promote sustainability and can be measured and tracked. Materials and systems continue to be developed to support these standards and enhance the performance of the building envelope.
Air tightness (i.e. air moving in and out through cracks, openings and places where different materials meet in a building) receives increasing attention because it impacts energy use. However there are other considerations for which air tightness is also important.
The amount of air flow through a commercial building can also determine how the heating and cooling systems perform, not simply in their energy use but for size, longevity and maintenance expense. Air quality, including humidity and moisture in the air is also affected by building air tightness.
Some of the key leakage pathways that affect building air tightness are found in open spaces and where different materials meet one another. Suspended ceilings, cavities elevator shafts, duct chase areas and breezeways area all obvious places where air leakage takes place. Some of the less obvious are leading doors and cracks on the top edge of windows.
The roof is a critical area for air tightness in a commercial structure. Because air flow tends to push toward the top of the building, it’s possible to lose large volumes of warm air generated by heating. Cool air being produced by A/C units can also be pushed out.
Specifications requiring air tightness, created by materials which construct continuous air barriers are being selected in many retrofits, and in new construction Bottom line, air tightness, and thus air barriers are becoming a requirement, so roof designs including enclosure materials which prevent air leakage, and are installed to maximize efficiency are more common.
Polyiso (polyisocyanurate) is one of the most efficient materials for roof insulation in a specification requiring air tightness. When installed correctly, it adds use as an air barrier because if its closed-cell construction. It’s a material renowned for efficient R-value (it has the highest R-value per square inch of any manufactured insulation product). When used with a facer, proper fasteners and staggered at it’s joints in multi-layers, it can create a virtually air-tight surface while adding integrity to the structure which can sometimes eliminate the use of a coverboard.
In most large low slope applications, a coverboard may still be required. To achieve air tightness, required insulation R-values and the strength needed for installation traffic and maintenance, a lightweight coverboard combining polyiso with a sturdy construction glass facer can be used.
Innovative products such as Atlas Roofing® Corporation ACFoam® HS CoverBoard provide the strength of a coverboard while adding a layer of polyiso insulation. The combined strength, insulating value and air tight properties of the closed cell-polyiso laminated with the glass facer delivers multiple efficiencies to the roof portion of the envelope.