Roofing Felt / Underlayment
Roofing underlayment serves two purposes: It is nailed to the roof deck so roofers have a better surface to walk on. It also provides a protective water resistant barrier between the roof decking and the shingles. This product is typically made from synthetic paper or tar paper (note most manufacturers for warranty purposes require their brand specific underlayment, please see photos above).
Underlayment roofing goes below the shingles and above the roof deck beginning at the eve and working up the slope. Rolls should be lapped a minimum of two inches and depending on the slope can be up to six inches. It should be lapped over the eve and drip edge, and it should be lapped under the Gable Rake drip edge.
Because underlayment is considered a standard part of the re-roofing process this product would generally be covered by insurance, if the roofing project on a whole is an insurance covered project. Although insurance does oftentimes only pay for comparable materials to what was already previously on the roof. It is worth noting that there are different types and weights of underlayment, and the insurance company will take that into account when determining what they will or won’t cover. Specific situations such as minor roof repairs may find the underlayment to still be in usable shape even if the shingles above it are not, so this situation is best determined with the help of your insurance adjuster and general contractor.
Insurance companies tend to pay for 30lbs underlayment on steep roofs that are 7/12 and above. 15lbs underlayment is used on 7/12 and below roofs that are less steep. Once you reach a 3/12 roof it typically changes over to Ice and Water Shield. Keep in mind owners can still decide to upgrade to synthetic felt or a heavier weight if they want to pay the difference and get the extra value of a warranty out of it.
The reason insurance companies will pay for thicker underlayment on steep roofs is because thinner underlayment is more prone to tearing when it’s walked on on a steep roof. Button cap nails are suggested in place of staples on felt because staples tear easily while button nails help to spread out the resistance across a larger area.
New synthetic underlayments are safer, stronger and offer better water resistance than traditional asphalt felt – synthetic underlayment is created by weaving polypropylene and polymer together – creating a water and vapor resistant substance. By code roofs must have underlayment installed/woven over unventilated ridges and/or hips.
There are several code enforced documents that describe how to install underlayment.
“Fasteners are to be applied along the overlap not farther apart than 36 inches on
“…12” between side laps with a 6” spacing at the side laps.”
“…All laps should be a minimum of 4”.”
“Underlayment should be attached using metal or plastic cap nails…”
GAF Technical Bulletins
“For hips the underlayment should be lapped over the hips at least 4”…”
“Use a 12 to 18” strip of underlayment to run along the hip and overlap the new
underlayment on the replacement plain at least 6’ to 12”.”
“For Ridges the underlayment should be lapped over the ridge at least 4 inches.”
“Use a 12” (305mm) to 18” (457mm) strip of underlayment to run along the hip
and overlap the new underlayment on the replacement plane at least 6” (152mm) to 12”
“For ridges, the underlayment should…be lapped over the ridge at least 4 inches…”