Roof Underlayment Types: Felt vs Synthetic for Minnesota Homes

Roof Underlayment Types: Felt vs Synthetic for Minnesota Homes

Roof underlayment is the critical barrier between your shingles and your roof deck — and for Minnesota homes, choosing the right underlayment type can mean the difference between a roof that protects your home for decades and one that fails prematurely. While homeowners often focus on shingle selection, the underlayment beneath those shingles plays an equally important role in waterproofing, longevity, and ice dam protection. Weatherguard Construction, serving Stillwater, Woodbury, Minneapolis, and the Twin Cities metro, installs premium underlayment on every roof replacement project.

What Is Roof Underlayment and Why Does It Matter?

Roof underlayment is a water-resistant or waterproof material installed directly on top of your roof decking (plywood or OSB sheathing) and beneath the shingles. It serves several critical functions:

• Secondary water barrier: If wind-driven rain, ice dam meltwater, or a damaged shingle allows water past the primary shingle layer, the underlayment helps prevent it from reaching the decking and your home’s interior.
• Moisture management: Underlayment can limit condensation and moisture migration between the attic and roof surface when paired with proper attic ventilation.
• Code compliance: Minnesota Residential Code requires underlayment on all asphalt shingle roofs.
• Shingle performance: Underlayment provides a smooth, consistent surface for shingle installation and helps shingles lay flat.
• Temporary dry-in: Quality underlayments protect the deck if weather pauses a project during installation.

In Minnesota’s climate — with heavy snowfall, ice dams, wind-driven rain, and dramatic freeze–thaw cycles — the underlayment’s role is even more critical than in moderate climates.

Felt Underlayment (Tar Paper)

What Is Felt Underlayment?

Felt underlayment, commonly called tar paper, has been used in roofing for over a century. It’s made from a base mat of organic fibers (cellulose) or fiberglass saturated with asphalt. Modern products are typically designated by ASTM type rather than true “pound” weight:

• Type I (often called “15-lb”): Thinner, used for standard applications, meets minimum code in many cases.
• Type II (often called “30-lb”): Thicker, more durable, with better water resistance.

Pros of Felt Underlayment

• Lower material cost: Felt is one of the most affordable underlayment options.
• Proven track record: Decades of successful use in residential roofing.
• Breathable: Allows some moisture vapor to pass through, which can help in certain ventilation scenarios.

Cons of Felt Underlayment for Minnesota

• Absorbs moisture: Felt can absorb water and wrinkle or buckle when wet, creating an uneven surface under shingles — a concern with snow load and ice dam conditions.
• Tears more easily: More fragile during installation; can tear in windy conditions or from foot traffic.
• Limited exposure rating: Deteriorates quickly in UV if left exposed during multi-day installations.
• Heavier to handle: Heavier than many synthetic alternatives, which can slow installation.
• Shorter lifespan: Degrades faster than synthetic materials, especially in moisture-heavy, freeze–thaw environments.

Synthetic Underlayment

What Is Synthetic Underlayment?

Synthetic underlayment is typically made from woven or non-woven polypropylene or polyethylene. It represents a significant advancement over traditional felt and has become the preferred choice for quality roofing contractors nationwide, especially in cold-weather regions.

Pros of Synthetic Underlayment for Minnesota

• Superior water resistance: Repels water without absorbing it, maintaining protective properties even when wet.
• Exceptional tear resistance: Commonly 5–10x stronger than felt, resisting tears from foot traffic, tools, and wind during installation.
• Lightweight and fast to install: Easier for crews to handle, especially on steep or complex roofs.
• Higher UV resistance: Many products are rated for extended exposure (often 60–180 days; always follow manufacturer limits) — helpful if Minnesota weather delays project completion.
• Lays flat: Won’t wrinkle like wet felt, providing a smoother surface for shingle installation.
• Longer service life: Synthetic materials maintain performance longer than organic felt.
• Safer walking surface: Most synthetics include textured, slip-resistant surfaces for crew safety.
• High-temp options: Available variants resist elevated temperatures under metal accents or dark shingles and around solar arrays.

Cons of Synthetic Underlayment

• Higher material cost: Typically 2–3x the cost of felt per square of roof area.
• Vapor permeability varies: Some synthetics are less breathable than felt and rely on properly designed attic ventilation for moisture control.
• Fastener requirements: Most manufacturers require cap nails or staples for best performance; following specifications is essential for warranty coverage.

Ice and Water Shield: Minnesota’s Essential Underlayment

Beyond standard underlayment, Minnesota Residential Code continues to require a self-adhering ice and water barrier (also called “ice barrier” or “ice and water shield”) in areas vulnerable to ice damming and concentrated water flow. These membranes are typically modified bitumen (SBS) or butyl-based with a peel-and-stick backing. When penetrated by a roofing nail, the membrane self-seals around the fastener, creating a watertight barrier — a key defense against ice dam leaks.

Required and recommended locations include:

• Eaves: From the eave edge to a point at least 24 inches past the interior wall line (measured horizontally). This commonly equals two courses (approximately 6 feet) on many Minnesota homes, depending on roof pitch and overhang depth.
• Valleys: Where two roof planes meet and channel heavy water flow.
• Around penetrations: Chimneys, skylights, vent pipes, sidewalls, and roof-to-wall intersections.
• Low-slope areas: Roof sections with pitches below 4:12 often require enhanced underlayment methods; many contractors use self-adhered membranes for added security.
• High-heat zones (as applicable): Use high-temperature-rated ice barrier under metal accents or exposed dark metal valleys.

Weatherguard often goes beyond code minimums for added protection in ice-prone areas like Lakeville, Burnsville, and Apple Valley, such as extending eave coverage, protecting rake edges, or fully covering low-slope porch roofs.

Which Underlayment Does Weatherguard Construction Recommend?

For Minnesota homes, synthetic underlayment paired with code-compliant (or better) ice and water shield delivers the most dependable performance. The combination of synthetic underlayment’s superior water resistance, tear strength, and longevity with self-adhered ice barrier at critical locations provides robust protection for Minnesota’s demanding climate. The modest cost increase over felt is one of the best long-term investments in a roofing system.

As an Owens Corning Platinum Preferred Contractor, Weatherguard installs Owens Corning ProArmor or Deck Defense synthetic underlayment and WeatherLock ice and water barrier products — backed by the Owens Corning Total Protection Roofing System warranty.

The Owens Corning Total Protection Roofing System

Underlayment doesn’t work in isolation — it’s part of a complete roofing system that includes shingles, underlayment, ice and water shield, starter strips, hip and ridge caps, ventilation, and flashing. The Owens Corning Total Protection Roofing System ensures all components work together for maximum performance.

By using compatible Owens Corning components throughout the system, Weatherguard can offer some of the strongest warranty coverage available — including the Platinum Protection Limited Warranty available through Platinum Preferred Contractors.

Get the Right Underlayment for Your Minnesota Roof

Don’t leave your roof’s secondary defense to chance. Request a no-pressure consultation to learn how Weatherguard’s premium underlayment systems protect homes through Minnesota’s toughest weather.

Call (651) 439-4320 or book your free roof inspection. Weatherguard serves homeowners across Minnesota from Stillwater, plus communities in Illinois and Colorado. MN LIC #BC282484. BBB A+ Rating. NRCA Member.

Frequently Asked Questions

Is synthetic underlayment worth the extra cost over felt?

Yes — especially in Minnesota. Synthetic underlayment offers better water resistance, tear strength, UV stability, and long-term performance in freeze–thaw conditions. On a typical Twin Cities home, the material cost difference is often in the range of $300–$800 depending on roof size and product selection — a small fraction of the total project cost with outsized benefits.

How much ice and water shield does Minnesota code require?

Minnesota Residential Code requires ice barrier from the eave edge to a point at least 24 inches past the interior wall line (measured horizontally). Practically, this often equals two courses (about 6 feet) on many roofs, depending on pitch and overhang. Valleys and roof penetrations should also be protected. Local amendments can vary; Weatherguard installs to current code and often exceeds minimums in high-risk areas.

Can I install new underlayment over old underlayment?

For a proper roof replacement, all old shingles, underlayment, and ice barrier should be removed down to bare decking. This exposes any hidden deck damage and ensures the new underlayment adheres correctly. While code allows limited “roof-over” scenarios, most manufacturer system warranties — and Weatherguard’s standards — call for a complete tear-off.

Does underlayment affect my roof warranty?

Yes. Using manufacturer-specified underlayment and following installation requirements (such as fastener type and exposure limits) are typically required to maintain full system warranty coverage. Weatherguard’s Owens Corning system approach helps ensure comprehensive warranty protection, including eligibility for Platinum Protection coverage through Platinum Preferred status.