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Indoor airPLUS

Technical Guidance to the Indoor airPLUS Construction Specifications

1. Moisture Control

Sections 1.7 - 1.10: Water-Managed Roof Assemblies

Best Practice: Roofing Underlayment Upgrade

No. 30 roofing felt, or an equivalent roofing underlayment (i.e., one that is stronger and has a longer service life than No. 15 roofing felt), can be applied to the roof deck before installing shingles or other roofing products.


No. 30 felt or equivalent products provide a more durable secondary weather barrier under the roofing material than does No. 15 felt. Other specialty underlayment products offer this same improved durability. Many of these are used on other types of roofing systems, such as membrane roofs.


No. 30 roofing felt is installed in the same manner as No. 15 felt, but because of its additional thickness and weight the material it is a bit more difficult to handle. For other products, follow the manufacturer’s recommendations.

References/Additional Information

  • Moisture-Resistant Homes – A Best Practice Guide and Plan Review Tool for Builders and Designers, U.S. Department of Housing and Urban Development, Office of Policy Development and Research, March, 2006. See www.huduser.org/Publications/pdf/moisturehomes.pdf exiting epa
  • Roof Underlayment for Asphalt Shingle Roofs, Home Builder's Guide to Coastal Construction, Federal Emergency Management Agency, Technical Fact Sheet No. 19, FEMA 499, August, 2008. See www.fema.gov/rebuild/mat/mat_fema499.shtm

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