What underlayment does

Underlayment sits between your roof deck and your shingles. It serves as the second line of defense when water gets past the shingles — during wind-driven rain, at damaged shingle areas, or during the period between tear-off and installation. It also provides a temporary weather barrier during installation when the crew stops at the end of a day or is delayed by weather.

Felt paper — the old standard

Traditional roofing felt (15 lb or 30 lb) is asphalt-saturated organic felt paper. It was the industry standard for decades and is still code-compliant. However, felt has significant limitations:

  • Absorbs water when saturated — swells, wrinkles, and can slip on steep slopes when wet
  • Tears relatively easily during installation foot traffic
  • Degrades faster under UV exposure when left exposed between tear-off and installation
  • Heavier — more weight on the structure

30 lb felt is meaningfully better than 15 lb for secondary protection but still inferior to modern synthetic products.

Synthetic underlayment — the current standard

Synthetic underlayment (woven or non-woven polypropylene or polyethylene) has largely replaced felt as the industry standard for quality installations. The advantages are significant:

  • Does not absorb water — remains flat and stable when wet, won't wrinkle or slip
  • Higher tear strength — better withstands foot traffic and wind before shingles are installed
  • Lighter — easier to handle and less structural load
  • Better UV resistance — can be left exposed longer without degradation
  • Non-slip surface on most products — important for crew safety on steep slopes

What Atlas Roofing installs

Atlas Roofing uses GAF FeltBuster synthetic underlayment as our standard on every complete roof replacement. It provides superior secondary waterproofing compared to felt paper, handles Northeast Ohio's weather delays and wet installation conditions better, and qualifies for GAF System Plus warranty eligibility as part of the full GAF system.

Ask your contractor: A quote that says "underlayment included" without specifying the type may mean 15 lb felt — the minimum code requirement but the least protective option. Ask specifically: "what underlayment product do you use?" The answer tells you a lot about the contractor's standard of installation.