What is the best roofing underlayment for a garage in the Oromocto NB area?

The best roofing underlayment strategy for a garage in the Oromocto area combines self-adhering ice and water shield membrane at the eaves, valleys, and penetrations with a high-quality synthetic underlayment over the remaining roof deck. This two-product approach provides the maximum protection against NB's ice dams, wind-driven rain, and heavy snow loads while keeping costs reasonable.

Oromocto sits along the Saint John River in south-central New Brunswick, where winters bring consistent snow accumulation, regular freeze-thaw cycles, and the potential for significant ice damming. The NB Building Code requires ice and water shield extending a minimum of 36 inches up from the eave edge on all sloped roofs, but experienced Oromocto-area roofers typically recommend 48 to 72 inches of coverage from the eave. This extended coverage protects against the ice dam backup that is common when snow melts on the upper roof and refreezes at the colder eave. For a typical two-car garage, the ice and water shield portion of the underlayment costs $300 to $700 depending on coverage area, with premium products like Grace Ice & Water Shield, Blueskin, or Resisto running $1.00 to $1.50 per square foot.

For the remainder of the roof deck above the ice and water shield zone, synthetic underlayment has become the clear standard over traditional #15 or #30 asphalt-saturated felt paper. Synthetic products like GAF FeltBuster, Titanium UDL, or Sharkskin outperform felt in virtually every category that matters in NB's climate. They are lighter, stronger, and far more resistant to tearing during installation and under wind stress. They do not absorb water or wrinkle when exposed to rain, which matters because NB weather can change rapidly and a partially shingled garage roof may sit exposed overnight. They also provide better traction for roofers working on the surface, improving safety. Synthetic underlayment runs $0.15 to $0.30 per square foot for materials, adding approximately $150 to $300 to a two-car garage roof.

Why Felt Paper Falls Short in NB

Traditional #15 felt paper was the standard underlayment for decades, and it still meets minimum code requirements. However, it has significant drawbacks in NB's climate. Felt absorbs moisture and wrinkles when wet, creating bumps under the shingles that are visible from the ground. It tears easily in wind, meaning any delay in shingling can leave the roof deck exposed. And it deteriorates rapidly under UV exposure — if your garage project is delayed and the underlayment sits exposed for more than a few weeks, felt can degrade to the point of needing replacement. #30 felt is heavier and more durable than #15 but shares the same moisture absorption problems. For these reasons, synthetic underlayment is worth the modest price premium for any NB garage.

A few additional underlayment details specific to the Oromocto area. If your garage has valleys where two roof planes meet, or areas where the garage roof meets a house wall (common on attached garages), these should be covered with ice and water shield, not just synthetic underlayment. Valleys concentrate water flow, and wall-to-roof connections are prime locations for ice dam backup and wind-driven rain infiltration. Pipe flashings, exhaust vents, and any other roof penetrations should also have ice and water shield extending at least 12 inches in all directions around the penetration.

For garages with metal roofing rather than asphalt shingles — a popular choice in the Oromocto area for its snow-shedding properties — a high-temperature synthetic underlayment is recommended. Metal roofing can reach surface temperatures above 75 degrees Celsius in summer sun, and standard underlayment products can degrade under sustained heat. Products labelled for use under metal roofing, such as Sharkskin Ultra or Titanium PSU-30, are designed for this application.

The total underlayment cost for a two-car garage in the Oromocto area, including ice and water shield at the eaves and valleys plus synthetic underlayment on the remaining deck, typically runs $500 to $1,000 — a fraction of the overall roofing budget but one of the most important layers in protecting your garage from NB's demanding climate. Any reputable roofing contractor will specify these products as part of their quote. If you need a roofer for a garage project in the Oromocto area, New Brunswick Garages can match you with local professionals through the New Brunswick Construction Network.