What is underlayment?
Underlayment on a roof is an asphalt saturated felt or synthetic material applied directly to the decking that serves as an added layer of protection against moisture reaching your attic.
What do I need to know about underlayment?
In Denver, with the weather coming from all directions, an adequate underlayment is essential. Any moisture, especially wind-driven rain may find its way underneath the shingles. With proper installation of your roof system that water will reach the underlayment, run to the eave, off the drip edge, and into the gutter. If improper or inadequate underlayment was used the water may stay on the decking, saturating it.
The type and weight of underlayment depend on multiple factors, many of which are set by local building codes. Roof slope, roof covering type (shingle, tile, slate, etc.), and geographic location of your home all factor in. Most commonly you will see #15 and #30 asphalt saturated sheets.
Relatively new to the market are synthetic underlayment materials, a polypropylene woven fabric designed to be lighter and stronger than traditional asphalt felt. Like any other tradition vs. new technology debate, everybody has their own opinions. Synthetic materials certainly are lighter, stronger on average, and do have a higher water resistance capacity. Asphalt underlayment advantages are more from an installers point-of-view. It’s easier to install in windy conditions, less slippery when debris is present, holds a chalk line for lining up shingles, and of course, it’s been the proven material for years past.
How should underlayment be properly installed?
Before installing any underlayment, it is imperative that the decking is completely clean of all debris and especially dry. Trapping moisture under the underlayment can result in interior and exterior troubles with your roof, from structural warping to visible waves in your shingles.
Underlayment should be installed over the decking on your entire roof, except where an ice and water barrier product is used. Also, be sure to not cover a ridge that is a part of your attic’s ridge venting system. Underlayment may be run over penetration openings, however, be sure to immediately mark these penetrations clearly so nobody steps in that spot. At the eaves, the underlayment should run over your drip edge, and under at the rakes. All seams should be lapped per the manufacturers’ standards.
Use cap nails to secure the underlayment to the decking, ensuring the underlayment is flat against the roof, with no waves. In the event you have all the decking laid and nailed, and you find a wave in the material, do not cut and lap the pieces to flatten it. That creates a seam for water to potentially enter your home. You should remove the nails from the affected area, flatten the underlayment, and re-secure it to the decking.
If you have any questions regarding the underlayment on your roof or any other roofing concerns, contact us for a free consultation.