How Long Can Roof Underlayment Be Exposed Before Shingles Go On?

How long can roof underlayment be exposed?

It depends on the product, and the Florida evaluation for a product can be stricter than its data sheet. Some are 30 days, some are 180.

Underlayment is the layer under your shingles. Owens Corning's glossary describes it as asphalt-saturated felt or a specially engineered synthetic material used beneath roofing to give the deck more protection. It is meant to be covered. Every maker sets a limit on how long it can sit in the sun and weather before the roof covering goes on. Here are the limits we found in documents we opened.

Read the table as examples, not a rule for every roof. The limit that counts is in the installation instructions and the Florida approval for the exact product on your roof. Those papers get revised, and a newer version may say something different from the ones we read. Atlas's Florida evaluation says that where the report, the code and the maker's instructions disagree, the more restrictive and code-compliant detail wins. When two limits are listed, plan to the shorter one.

This page covers synthetic underlayment. Felt has its own limits. See our guide to synthetic underlayment versus felt for how the two compare.

What does underlayment exposure mean in the middle of a roof replacement?

A roof is only as dry as its weakest day. Plan the tear-off so the crew can cover what they open before the limit and before the weather turns.

On a roof replacement, the crew removes the old roof down to the deck, installs underlayment, then installs the shingles or other roof covering on top. A longer gap between those steps can come from a storm forecast, late material, a permit or inspection hold, or a decision that is still pending. The longer the gap, the more the underlayment is doing a job it was only meant to do for a short time. Our guide on what to expect during a roof replacement walks through the whole job in order.

You do not need to know every product. You do need to ask a few plain questions before the tear-off starts.

1. Which underlayment is going on my roof?

   Ask for the brand and product name. Ask where the exposure limit is written, and ask to see it.

2. How much of my roof will be open at one time?

   A smaller open area is easier to cover quickly. Ask how the crew splits the roof into sections.

3. What is the plan if the weather turns?

   Ask who covers the roof, with what, and how fast. A tarp is a short-term fix. See how long a tarp can stay on a roof.

4. What happens if the job stalls past the limit?

   Ask whether the roofer will check the underlayment and replace it if needed, and ask for that in writing.

5. Will I get dated photos?

   Ask for photos of the deck and the underlayment before the shingles go on. Coastline sends a written photo report with inspections. On a replacement, ask any roofer for dated photos.

Felt, synthetic and peel-and-stick: what is the difference?

They are different products with different limits, so a number for one does not apply to another.

Owens Corning's glossary defines felt as fibrous material saturated with asphalt. It describes synthetic underlayment as typically made from polypropylene and used as an alternative to felt. It describes self-adhering shingle underlayment as a waterproofing product designed to protect against water getting in from wind-driven rain, and says the code requires it to meet ASTM D1970 and carry that label.

Florida also requires roofing products to be approved. Under Florida Statute 553.842, roofing products need statewide approval before they are used. The approval documents are where exposure limits like the ones above are written. See our guide to Florida product approval for roofing to learn how to look one up.