Residential Roofing: How to Install Synthetic Underlayment (The Right Way)

Installing synthetic underlayment properly is one of the most important steps in making a roof weather-tight. Whether you’re in Denver or Atlanta, getting this layer right ensures long-term protection against water, wind, and UV exposure.

Here’s what you need to know.

Why Choose Synthetic Underlayment Over Felt?

More homeowners and contractors are switching to synthetic underlayment—and for good reason:

• More durable: Synthetic options resist tearing, even under foot traffic.

• Better UV resistance: Some products withstand up to 6 months of UV exposure.

• Safer to walk on: Slip-resistant surfaces improve installer safety.

• Lighter weight: Easier and faster to install than felt rolls.

• Longer-lasting protection: Better water-shedding and weather barrier.

Before You Start: Prep and Materials

1. Clean the deck: Remove dust, nails, or old roofing debris. Decking must be dry and smooth.

2. Inspect the deck: Replace any damaged or rotted OSB or plywood.

3. Choose the right product: Match your underlayment’s specs to your local code and roof covering (shingles, metal, tile).

4. Gather tools:

   • Cap nails or plastic cap staples

   • Utility knife

   • Chalk line

   • Tape measure

   • Hammer tacker (if allowed by local code)

Installation Steps

1. Start at the Eave

• Lay the first course horizontally, parallel to the eave.

• Overlap the drip edge by 1"–2", or install drip edge over the underlayment if required by code (e.g., IRC Section R905.1.1).

• Leave a 6" overhang into the gutter where applicable.

2. Fasten Correctly

• Use plastic cap nails or cap staples.

• Space fasteners 12" apart along the horizontal lap and 24" apart vertically.

• DO NOT staple or nail in valley areas unless manufacturer instructions allow it.

3. Overlap Properly

• Horizontal laps: 4" minimum

• Vertical laps: 6" minimum

• Ridge overlap: Wrap 6" over the peak, then cover with ridge cap or ridge vent.

4. Watch the Weather

• Only install underlayment on dry decks.

• Don’t install in high wind—secure immediately if windy weather is expected.

Extra Tips for Colorado and Georgia

• In Colorado: Add ice and water shield at the eaves if you're in Zone 6 or higher (per IRC Section R905.1.2).

• In Georgia: Heat and humidity demand synthetic underlayment with excellent moisture and mold resistance. Look for ASTM D1970-compliant products.

FAQs

What’s the best fastener for synthetic underlayment?

Cap nails or plastic cap staples. Avoid standard staples—they can void manufacturer warranties.

Do I still need ice and water shield?

Yes—especially in valleys, eaves, and around roof penetrations. Synthetic underlayment is not a replacement for ice dam protection.

Can I leave synthetic underlayment exposed?

Some products allow up to 180 days of exposure, but always check the specific manufacturer's limit.

Call Roof Nuts Today

Need help with your residential roof? Roof Nuts serves homeowners across Colorado and Georgia with certified installation of roofing systems—backed by trusted materials and expert crews.

• Colorado: RoofNutsCO.com | Call 303-276-2403

• Georgia: RoofNutsGA.com | Call 404-476-6851

Let’s keep your home covered the right way—starting from the underlayment up.