Roof Anatomy
What is Underlayment?
Roofing Glossary · Roof Anatomy
Definition
A water-resistant or waterproof barrier material installed directly over the roof decking and beneath the finish roofing material. Underlayment serves as a secondary line of defense against water infiltration if shingles are damaged or wind-lifted. Modern options include synthetic underlayment (superior tear resistance and moisture control) and traditional felt paper (No. 15 or No. 30 asphalt-saturated felt).
Related Roofing Terms
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Ice and Water ShieldA self-adhering, waterproof membrane installed on the roof deck in vulnerable areas — typically the ...
→DeckingAlso called sheathing, the decking is the structural boards or panels — typically 7/16" or 1/2" OSB ...
→SheathingA synonym for roof decking — the layer of structural panels (OSB or plywood) attached to the roof fr...
→Synthetic UnderlaymentA non-woven polypropylene or polyester fabric used in place of traditional felt paper beneath roof s...
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