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. At Weatherguard Construction, serving Stillwater, Woodbury, Minneapolis, and the Twin Cities metro, we install 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 prevents it from reaching the decking and your home''s interior
  • Moisture management: Underlayment controls condensation and moisture migration between the attic and the roof surface
  • Code compliance: Minnesota building code requires underlayment on all asphalt shingle roofs
  • Shingle performance: Underlayment provides a smooth, consistent surface for shingle installation and helps shingles lay flat

In Minnesota''s climate — with heavy snowfall, ice dams, wind-driven rain, and dramatic temperature swings — 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. It comes in two common weights:

  • 15-lb felt: Thinner, single-layer applications, minimum code requirement
  • 30-lb felt: Thicker, more durable, better water resistance

Pros of Felt Underlayment

  • Lower material cost: Felt is the most affordable underlayment option
  • Proven track record: Decades of successful use in residential roofing
  • Breathable: Allows some moisture vapor to pass through, which can be beneficial 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
  • Tears easily: Felt is more fragile during installation and can tear in windy conditions or from foot traffic
  • UV degradation: If left exposed (such as during multi-day installations), felt deteriorates rapidly in sunlight
  • Weight: Heavier than synthetic alternatives, making handling more difficult
  • Shorter lifespan: Felt degrades faster than synthetic materials, especially in moisture-heavy environments like Minnesota

Synthetic Underlayment

What Is Synthetic Underlayment?

Synthetic underlayment is 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.

Pros of Synthetic Underlayment for Minnesota

  • Superior water resistance: Synthetic underlayment repels water without absorbing it, maintaining its protective properties even when wet
  • Exceptional tear resistance: 5–10x stronger than felt, resisting tears from foot traffic, tools, and wind during installation
  • Lightweight: Easier for crews to handle and install, especially on steep roofs
  • UV resistant: Can be left exposed for weeks or even months without degrading — important if Minnesota weather delays project completion
  • Lays flat: Won''t wrinkle or buckle like wet felt, providing a smoother surface for shingle installation
  • Longer lifespan: Synthetic materials last significantly longer than organic felt
  • Non-slip surface: Most synthetic products feature textured surfaces for better crew safety on steep slopes

Cons of Synthetic Underlayment

  • Higher material cost: Synthetic costs 2–3x more per square than felt
  • Vapor permeability varies: Some synthetic products are less breathable than felt, requiring proper attic ventilation

Ice and Water Shield: Minnesota''s Essential Underlayment

Beyond standard underlayment, Minnesota building code requires self-adhering ice and water shield membrane in specific areas prone to water infiltration from ice dams:

  • Eaves: Code requires ice and water shield from the eave edge to at least 24 inches past the interior wall line
  • Valleys: Where two roof planes meet and channel heavy water flow
  • Around penetrations: Chimneys, skylights, vent pipes, and wall intersections
  • Low-slope areas: Roof sections with pitches below 4:12

Ice and water shield is a rubberized asphalt membrane with a peel-and-stick adhesive backing. When penetrated by a roofing nail, it self-seals around the nail shaft, creating a watertight barrier. This self-sealing property is what makes it so effective against ice dam leaks.

At Weatherguard Construction, we go beyond code minimums on ice and water shield coverage. In areas like Lakeville, Burnsville, and Apple Valley, where ice dam activity is common, we often extend ice and water shield coverage for additional protection.

Which Underlayment Does Weatherguard Construction Recommend?

For Minnesota homes, we strongly recommend synthetic underlayment as the standard choice, combined with ice and water shield in all code-required and high-risk areas. Here''s why:

The combination of synthetic underlayment''s superior water resistance, tear strength, and longevity with ice and water shield at critical locations provides the best possible protection for Minnesota''s demanding climate. The modest cost increase over felt is one of the best investments you can make in your roofing system.

As an Owens Corning Platinum Preferred Contractor, we install Owens Corning ProArmor 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 matching Owens Corning components throughout the system, Weatherguard Construction can offer the strongest warranty coverage available — including the Platinum Protection Limited Warranty exclusively available through Platinum Preferred Contractors.

Get the Right Underlayment for Your Minnesota Roof

Don''t leave your roof''s secondary defense to chance. Contact Weatherguard Construction for a free consultation and learn how our premium underlayment systems protect your home through Minnesota''s toughest weather.

Call (651) 439-4320 or book your free roof inspection. We serve homeowners across Minnesota from Stillwater, plus communities in Illinois and Colorado. MN LIC #BC282484.

Frequently Asked Questions

Is synthetic underlayment worth the extra cost over felt?

Absolutely, especially in Minnesota. The superior water resistance, tear strength, and longevity of synthetic underlayment provide significantly better protection against our harsh weather conditions. The cost difference on a typical roof is only $200–$500 — a small fraction of the total project cost.

How much ice and water shield does Minnesota code require?

Minnesota code requires ice and water shield from the eave edge to a point at least 24 inches past the interior wall line. This typically means 3–6 feet up from the eave depending on roof pitch and wall placement. We often exceed this minimum for additional protection.

Can I install new underlayment over old underlayment?

No. During a proper roof replacement, all old shingles, underlayment, and ice and water shield should be removed down to the bare decking. This allows inspection of the decking for damage and ensures the new underlayment adheres properly. Weatherguard Construction always performs complete tear-offs for this reason.

Does underlayment affect my roof warranty?

Yes. Using manufacturer-specified underlayment products is typically required to maintain the full system warranty. Installing mismatched or inferior underlayment can void or limit your warranty coverage. Our Owens Corning system approach ensures complete warranty protection.