Synthetic underlayments have become a widespread substitute over customary felt papers, replacing both 15 lbs. and 30 lbs. for both asphalt and wood roofing. Felt paper is what it is: paper-based. Once it attracts moisture due to rain or overnight dew, it will wrinkle and curl and will lessen its capacity to remain flat. Synthetic underlayments have become a popular alternative as they can be left exposed on the roof for a month to 6 months provided roofers follow installation instructions, especially fastener details. Plastic cap staplers such as the “Stinger” work well. Some products claim longer exposure limits and will not have the rippling effect of felt papers.
However, many synthetic underlayments have a perm rating less than 1, meaning that they are impermeable. Although felt paper has a perm of 5–7, making them semi-permeable. There is documentation that the use of certain less permeable synthetic underlayments, combined with lack of inadequate ventilation of the roofing material, may cause problems with wood roofing. External heat, unable to pass through the underlayment, can cause the shingles to heat from the underside. This heat can trigger premature aging and a shortened lifespan of the wood shingles. The Cedar Shake & Shingle Bureau (CSSB) has addressed this phenomenon in their Roof Manual installation instructions. www.cedarbureau.org. To address the ventilation aspect of this occurrence, Cedar Breather isn’t adequate on its own. However, Cedar Breather in conjunction with semi-permeable or permeable underlayments, such as GAF Deck Armor which has a perm rating of 16, is an acceptable combination method for wood roof situations.
GAF Deck Armor provides a critical extra layer of protection between your shingles and your roof deck — to help prevent wind-driven rain (or water from other sources) from infiltrating under your shingles and causing damage to your roof structure or to the inside of your home. In addition, premium-quality roof deck protection will aid reduce trapped moisture from inside your attic, allowing it to escape (to help prevent structural decay, mold, and mildew).
These are some of the top reasons I would recommend you use GAF Deck Armor:
- Exceptionally Strong (at least 600% greater tear strength than standard #30 felt!†).
- Revolutionary Breathable Technology, which helps prevent inside moisture from becoming trapped within your roofing system—and possibly causing mold, mildew, and expensive structural damage.
- Premium Construction. It’s exceptionally durable, non-asphaltic construction will not rot or become brittle (unlike conventional asphalt felts, which can disintegrate over time).
- Long-Lasting Protection with up to a Lifetime Limited Warranty when installed on Lifetime Shingle roofs. Ask your Shepley salesperson for more information.
- Looks Better. Unlike conventional asphalt felts, Deck-ArmorTM Premium Breathable Roof Deck Protection resists wrinkling or buckling, so it lets your shingles lie flatter for a better-looking roof.
† GAF trapezoidal tear strength testing per ASTM
Kevin Brennan has over 35 years of experience in the building materials industry and joined Shepley in 2015 as the outside sales rep for the Outer Cape.
You can reach Kevin at 508-375-5323.