Winter Toll On Buildings

This winter has been a textbook lesson on the toll weather can take on our buildings. We have had snow and ice on the ground (and roof) for many consecutive weeks without any sustained thaws to completely remove the snow. The freeze-thaw cycle has resulted in ice damming on roofs that we haven’t experienced for many winters. Outside temperatures above freezing or a warm roof surface due to poor insulation will cause snow to melt on the roof surface. When the melted snow runs down the roof and hits a cold surface, such as a roof eave overhang, gutter or flashing, the water freezes creating a “dam” that grows in thickness as more water runs down the roof and freezes. Water backs up behind the dam, eventually working its way beneath the roofing and into the building.

Mother Nature is reminding us that we need to pay close attention to our building envelope detailing. Attics need to be well insulated and ventilated in order to keep the roof surface cool during winter months. Regardless of the roofing material, roof eaves and valleys need to be protected with self-adhering roofing underlayment to prevent water from infiltrating beneath the roofing. Eave, fascia, and gutter flashing should be carefully detailed with positive drainage and joints overlapped. Refer to SMACNA manuals for approved gutter and flashing details. In some cases snowmelt panels or cabling is required on the roof eaves, valleys and gutters to keep snowmelt running all the way to the bottom of the downspout and away from the building where it belongs. Finished grade should be sloped away from the building to direct roof drainage and ground level runoff away from the building.

We certainly can’t control the weather, but keeping building envelope fundamentals in mind when detailing buildings can go a long way in preventing future weather-related problems.

Kory Kennaugh, AIA, LEED AP, GGP- Vice President