Fixing ice dams with ventilation

The roofing material on any building — metal or not — is an important part of a complete roofing system. Keep in mind it works only with proper framing, underlayment, insulation, ventilation and fastening. Any installation error or omission creates a faulty system and then reflects on each component of the system, including the roofing.

Why is ventilation an important part of the roofing system? According to

“Proper attic ventilation extends the life of a roof and reduces problems because it minimizes the temperature differential between the attic and the air outside. Proper ventilation will remove moisture and heat from the attic. Trapped heat and moisture can raise energy costs, cause ice dams, and damage roof system components as well as structural and personal items located inside the attic where temperatures can easily reach 150 degrees. In some cases the condensation can be bad enough to be mistaken for a roof leak.”

Just outside Minneapolis, this two-story office park, comprised of several similar buildings, has been plagued with leaks near the eaves caused by ice dams. The cause: no ventilation.

A couple years ago, a roofer tore off the wood shakes and installed an asphalt shingle on a couple of the buildings — it wasn’t solving the problem.

Cliff Vosburg of Absolute Construction & Remodeling of Maple Grove, Minn., was called onto the scene to lend his expertise. Vosburg offers a variety of building and remodeling services, including the installation of metal roofing from Metro Roof Products.

Vosburg says the office building’s original roofing system consisted of foam insulation panels (5×8 foot sheets), topped by plywood decking, metal foil, tar paper and wood shakes. The foil, tar paper and shakes were all stapled into the decking.

Gaps between the panels of foam insulation allowed for heat loss and condensation on the metal foil. The lack of ventilation led to the condensation eventually rotting the plywood decking. That led to more heat loss, ice dams and leaking, leaving the wood shakes unattached.

Vosburg wasn’t able to assess all of the damage until the wood shakes were removed, but much of the plywood decking had to be replaced — after the gaps between the foam insulation were filled in.

Vosburg’s crew covered the new plywood with Feltex synthetic underlay-ment and used Pro Master rolled ridge vent from Berger Building Products for ventilation at the eaves and ridge. The system was topped off with Metro’s Shake shingle, which sits up enough to allow ventilation between the underlayment and the shingle. MR

For more information visit the sites of Metro Roof Products; Pro-Master from Berger Building Products; and Feltex.

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