Underlayment Code Upgrades: Forcing Full Synthetic Replacement

Written by Nathaniel Davis, owner of Roof Gutter Now — a licensed exterior restoration contractor in Ohio, Pennsylvania and New York. Updated August 2026

Underlayment is invisible once the roof is on, which is why it is the easiest line to under-scope. Code requirements are what put it back.

What the code requires

IRC R905.1.1 governs underlayment for asphalt shingle roofs, and R905.1.2 covers the ice barrier requirement in regions with a history of ice at the eaves. On a re-roof, underlayment is not optional and it is not reusable — it comes off with the shingles.

The ice barrier runs from the eave edge to at least 24 inches inside the exterior wall line. On a low-slope section or a steep pitch, additional layers may be specified by the manufacturer.

Where the estimate falls short

Two failures recur: felt written at a lower grade than the manufacturer’s system requires, and ice barrier omitted entirely because the original roof did not have it. The second is an ordinance and law item, not a like-for-like replacement item.

Submit the manufacturer specification for the shingle system being installed alongside the adopted code section for the jurisdiction, with the measured square footage. Specification plus code plus quantity is a complete argument.

Common questions