Underlayment
Underlayment is a water-resistant or waterproof barrier installed over roof decking before shingles, or a smooth layer placed over subflooring before finish floor installation.
Underlayment serves as a critical secondary barrier protecting your home from water infiltration and providing a smooth base for finish materials. In roofing, underlayment goes over the roof deck (OSB or plywood) before shingles or other roofing materials. It provides backup protection if water gets under shingles due to wind-driven rain, ice dams, or damaged shingles. Common types include traditional asphalt-saturated felt (#15 or #30) and modern synthetic underlayments.
Why It Matters in Denver
Denver's weather makes quality underlayment essential. Ice dams—formed when snow melts and refreezes at roof edges—can force water under shingles. Synthetic underlayment resists tearing, doesn't wrinkle when wet, and provides superior waterproofing compared to felt paper. For floors, underlayment creates a smooth surface over subfloors, reduces noise transmission, and provides moisture barriers for laminate or engineered wood installations. Modern building codes require underlayment in most applications.
Common Types and Applications
- Synthetic roofing underlayment: Lightweight, tear-resistant polymer sheets
- Ice and water shield: Self-adhering membrane for valleys, eaves, and vulnerable areas
- Felt paper (#15 or #30): Traditional asphalt-saturated option
- Floor underlayment: Cork, foam, or fiber sheets under laminate and engineered flooring
- Sound-deadening underlayment: Reduces noise transmission between floors
Related Terms
OSB (Oriented Strand Board)
OSB is an engineered wood panel manufactured from cross-oriented layers of wood strands bonded with resin under heat and pressure, commonly used for roof decking, wall sheathing, and subflooring.
Flashing
Flashing is thin, waterproof material (typically metal or membrane) installed at vulnerable points in a building envelope to direct water away from joints, seams, and penetrations.
Waterproofing
Waterproofing involves installing membranes, sealants, and drainage systems to prevent water from penetrating foundations, basements, showers, and other vulnerable areas.