Understanding Underlayments

Underlayments – Know your options…demand the best!

Roofing underlayment serves two purposes. Applied directly to the roof, its initial role is to protect the home from the elements while shingles are affixed to the roof. When the roof is completed, the underlayment assists as a secondary layer of protection for your roof beneath the shingle layer by repelling moisture and helping to lengthen the lifespan of your roof .

Historically, underlayment automatically meant 15lb or 30lb felt, a paper product that is literally soaked in asphalt. While felt paper is still the primary underlayment used today (largely due to low cost), Synthetic underlayments are also available which may offer better resistance to tearing and moisture protection. If you live in a part of the country that gets excessive moisture and/or ice dams, you may also want to consider a thicker moisture barrier at the eaves, referred to as ‘self-adhering’ underlayment. Self-adhering underlayments are traditionally used in conjunction with felt paper and seal up around nail holes.

Regardless which product you choose make certain that it can protect against the particular climate concerns of your local area.

Felt products are NOT waterproof, they are water resistant, and cannot be left exposed to UV rays and rain for more than 24-48 hours according to manufacturer specifications as the oil embedded in the felt will breakdown and dry out and cause it to lose its waterproofing properties. This can be problematic when installing a shingle product that is meant to last 30 years or more if the felt has broken down and is no longer watertight after 5-10 years because of improper care during the installation process.

Felt products must also remain COMPLETELY dry prior to installation. If the felt gets wet, the felt must be allowed to dry out prior to installing shingles to prevent moisture from becoming trapped and causing unsightly ripples in the underlayment as a result of absorption, contraction and expansion of the product. These ripples will telegraph through the finished shingles and leave unsightly ripples. Synthetic underlayments eliminate this problem, provide excellent traction when wet and best of all, can have shingles installed overtop without requiring the product to dry out.
Synthetic Underlayments will perform much longer, in most cases, up to 6 months exposed to UV and rain before the roof has to be installed. These types of underlayments require specific plastic cap fasteners to be used when installing. Staples and Roofing Gun Nails are NOT permitted as an accepted fastener as this can easily rip and cut into the synthetic material, causing leaks and endangering installers’ lives during the project.