What is roof underlayment?
Roof underlayment is a water-resistant layer of felt or synthetic material installed over the roof deck, beneath shingles or other roofing material, to provide secondary protection against moisture and extend roof durability.
Underlayment sits between your roof deck and the shingles or other roofing material you see from the street. It acts as a backup barrier in case water gets past the outer layer during heavy rain, snow melt, or wind-driven weather. When installed properly, it stops water from reaching the wood framing and insulation underneath, which can rot and cause structural damage if left wet.
Ontario roofing contractors typically use one of two types. Felt underlayment, also called tar paper, has been standard for decades. It is affordable and familiar to most installers. Synthetic underlayment, made from polymers or fiberglass, offers better grip during installation, resists tearing, and lasts longer without degrading in UV light. Synthetic costs more upfront but performs better in extreme weather and can extend the life of your roof system.
Building codes in Ontario require underlayment on most residential and commercial roofs. The choice between felt and synthetic depends on your budget, local weather exposure, and long-term durability goals. Contractors who install underlayment correctly, with proper overlap and fastening, ensure your roof investment is protected for its full lifespan.
When planning a roof replacement, roof replacement and installation providers in Ontario can advise which underlayment type suits your home and climate.