What is roofing underlayment?
Underlayment is a weather-resistant membrane or sheet material installed between the roof deck and shingles to block water penetration and protect against leaks.
The layer of material that sits directly above your roof deck and beneath your shingles serves as your home's secondary water defense. If rain gets past the shingles or wind-driven moisture finds gaps, underlayment catches it and channels it safely off the roof rather than letting it soak into the structure.
Two main types are common in Connecticut roofing work. Felt paper, also called tar paper, has been the traditional choice for decades. It is affordable and time-tested, though it absorbs water over time and deteriorates faster than modern alternatives. Synthetic underlayment, made from polypropylene or polyethylene, resists water absorption, withstands UV exposure longer, and won't rot. Many contractors now prefer synthetics because they perform better in wet conditions and on steep slopes.
Building codes and insurance requirements often specify underlayment type and coverage area. On most Connecticut homes, it covers the entire roof deck. On some jobs, it may extend only in valleys or along eaves where water risk is highest. The material must be installed with proper overlap and fastened so wind cannot lift or separate it during a storm.
Choosing the right underlayment affects how long your roof sheds water before leaks reach the interior. Quality roof replacement contractors select underlayment that matches your roof style, local weather patterns, and long-term durability goals.