PVC Roof Installation on Shed Dormer in North Attleboro, MA

A shed dormer is a very popular way to expand a living space without building an addition. Shed dormers have almost flat or very low pitched roofs, and if covered with regular roofing materials, like asphalt shingles or rolled asphalt, they tend to leak and allow ice dams to build-up. A rolled PVC membrane is the great solution to prevent leakages and ice dams. Not only it is designed for flat and low sloped roofs, it also carries the lifetime material warranty and has an extra benefit of reflecting a lot of sunlight, keeping cool the space under.

For this project, we decided to go with a 50-mil white PVC membrane, mechanically attached over ½ inch Styrofoam insulation. Originally there was one layer of asphalt shingles on the roof, but since the roof deck was in a great shape, we decided to leave them and go over the top, which essentially cut the cost for the homeowner. We cut back shingles along the edges, removed the old drip edge, and installed 6 inch wide pressure-treated nailer to allow proper PVC coated drip edge installation. In this case, we decided to weld membrane directly to the drip edge (as opposed to the method when drip edge goes on top of the membrane and then the 6-inch stripes are welded over), and we used extra screws every 6 inches to hold drip edge in place really tight.

Because this roof had a ridge vent on it, we installed a pressure-treated 2×4 stud along the ridge and wrapped it with pre-welded PVC flashing piece, to serve the purpose of a substrate for the new ridge vent and ridge cap installation.

Another possible problem is snow slide during the winter. Usually, it is not a problem on the flat or almost flat roofs but shed dormers usually have a substantial pitch (somewhere between 2 and 4). In addition, a wet PVC membrane is pretty slippery. These two issues can be causes of snow slide formation. Since our client had a big porch under the roof section where work was done, we decided to install plastic snow guards – every foot in a staggered formation. To ensure the proper installation, we installed another piece of 6-inch pressure-treated nailer one foot above the one along the edge prior to the membrane set up. We used special screws with rubber gaskets to hold the snow guards in place and we also used SolarSeal 900 sealant between the snow guard and the roof to cover the screws up. We also installed two 5 inch two-way vets to ensure proper condensate evaporation from under the membrane.