What Is Roofing Underlayment?

Roofing underlayment is a water-resistant or waterproof layer installed directly on the roof deck, beneath the primary roofing material (shingles, metal panels, etc.). It provides a secondary barrier against water infiltration if the outer roofing layer is breached by wind-driven rain, ice, or storm damage.

Why Underlayment Matters in New England

In Massachusetts and Rhode Island, underlayment is not optional - it's essential. Our climate brings:

• •Nor'easters with wind-driven rain that can force water under shingles
• •Ice dams that back water up under the roof edge
• •Heavy snowfall and freeze-thaw cycles that stress roofing materials
• •Summer thunderstorms with intense, localized rainfall

A quality underlayment acts as the last line of defense between a compromised outer layer and your home's interior.

Types of Roofing Underlayment

Felt (Asphalt-Saturated) Underlayment

Traditional roofing felt is made from recycled paper or fiberglass mat saturated with asphalt. Available in two weights:

**#15 Felt:**

• •Lighter weight, less expensive
• •Suitable for low-risk areas and some re-roof applications
• •Tear resistance is lower; can dry out and crack over time

**#30 Felt:**

• •Heavier, more durable
• •Better for steep-slope applications
• •More resistant to tearing during installation and storm events

Felt underlayment has been the standard for decades but has largely been replaced by synthetic options in new construction.

Synthetic Underlayment

Manufactured from woven or spun polypropylene or polyethylene, synthetic underlayments have become the preferred choice for most modern roof installations.

**Advantages over felt:**

• •Lighter weight (easier installation)
• •Much higher tear and puncture resistance
• •Better UV resistance (can be left exposed longer during construction)
• •Wrinkle-resistant for a smoother finished surface
• •Longer warranty periods

Roofing Doctors uses premium synthetic underlayment on all our standard roof replacements in Massachusetts and Rhode Island.

Ice and Water Shield

A self-adhering, rubberized asphalt membrane that provides a fully waterproof (not just water-resistant) barrier. It seals around fasteners, meaning even if nails are driven through it, it self-seals around the nail shaft.

**Required locations in Massachusetts and Rhode Island:**

• •Eaves: Minimum 6 feet from the edge (to protect against ice dam water backup)
• •Valleys: 18-36 inches on each side of the valley centerline
• •Around skylights, chimneys, dormers, and roof penetrations
• •Low-slope areas (less than 4:12 pitch)

The International Residential Code and Massachusetts Building Code both require ice and water shield at eaves and other vulnerable areas.

Underlayment and Ice Dams

In New England, the interaction between underlayment and ice dams is critical. When ice dams form at the roof edge, water backs up behind them and can work its way under shingles. Standard synthetic or felt underlayment is water-resistant but not fully waterproof - it will eventually allow water through if submerged long enough.

This is why the ice and water shield at the eaves is so important: it creates a fully waterproof zone at the most vulnerable area of the roof. Most Massachusetts building inspectors require a minimum of 6 feet of ice and water shield from the eave edge.

Underlayment Installation Order

1. Install drip edge at eaves

2. Apply ice and water shield from eave edge up (minimum 6 feet, or past the interior wall line)

3. Apply synthetic underlayment over the remaining roof deck, overlapping horizontal courses by 4-6 inches

4. Install drip edge at rakes (over underlayment)

5. Apply ice and water shield at valleys and penetrations

6. Install shingles or other final roofing material

What to Expect From Your Roofing Estimate

Every complete roof replacement should include:

• •Full tear-off of existing roofing materials
• •Inspection and repair of any damaged roof decking
• •New drip edge installation
• •Ice and water shield at eaves, valleys, and penetrations
• •Quality synthetic underlayment across remaining deck
• •New shingles or other primary roofing material

Roofing Doctors includes all these components in our standard roof replacement packages for Massachusetts and Rhode Island homeowners.