Wind Blown Rain and Ice Dam Barriers
DEAR TIM: It is time to install a new roof on my house. My roof is subjected to strong wind blown summer rains as well as deep snow in the winter. This past summer leaks developed during an intense storm. Will felt underlayment prevent these leaks? Is there another way to prevent these leaks? Do you have any installation tips for a DIY'r roofer? M. A.
DEAR M. A.: Wind blown rain is a big problem for many homes in the United States. Violent thunderstorms can produce very strong winds that will drive rain up under many roofing materials. Hurricanes produce violent sustained winds that can create indoor waterfalls. Interior water leaks are frequently produced by ice dams. Felt paper will not stop these leaks entirely.
Just about every roof covering depends upon gravity to keep water from entering your home. Slate, clay tiles, metal tiles, asphalt shingles are installed in an overlapping fashion. As you proceed up a roof, each successive layer of roofing material overlaps the row below. As long as water flows down the roof, this system works well. Metal flashings around chimneys and skylights require gravity as well to stop water penetration into your home. However, wind and ice dams cause water to travel backwards up the roof and behind metal flashings.
Once water gets behind roofing materials, there are numerous places it can enter your house. The wood sheathing beneath the roofing materials has cracks and seams. Felt paper has numerous holes from the nails which hold the roofing materials. All of these places allow water to enter your home. New membrane roofing products can be installed which stop these troublesome leaks.
The membrane roofing materials consist of rubberized asphalt which is often covered by a high density polyethylene plastic sheet. The rubberized asphalt seals around nails which penetrate this membrane. These products should be installed in locations where water can easily work its way beneath shingles or other roofing materials. Often these locations can be found at the lower edge of roofs, valleys (where two different roof surfaces meet), rake edges (roof edge), chimney and skylight penetrations, low slope roofs, and areas where roof slopes change.
These roof membranes are sensitive to ultraviolet light. They must be covered by regular roofing materials. Certain ones are available for people who have roofs in high temperature areas such as the southwest. The membranes stick to the wood deck surface and are lapped up onto sidewalls, chimneys, skylights, etc. to produce a watertight installation. Metal flashings, siding, etc. cover this membrane to protect it from sunlight and abuse.
Prior to starting your roofing project, obtain and read the installation procedures for the material you are using. Be sure you have the proper tools and accessories which will allow you to safely accomplish the project. Pay attention to the nailing requirements of the roofing material. For example, asphalt shingles often require a minimum of 4 nails driven at specific locations on each shingle to prevent leaks.
If your roof requires metal flashings, make sure you use a material such as tin, galvanized steel, or copper. These are metals that can be soldered. Don't discount copper because of its cost. You may only spend an extra $100 - 150 for a material that will never rust and is very easy to solder. Not only that, copper flashings, copper coated shingles, granules and copper strips will prevent the unsightly roof algae that affects many roofs. Don't use aluminum flashing material in contact with brick or other masonry structures. The lime in the mortar will corrode the aluminum!