IRC R908 Reroofing: When an Arizona Roof Must Strip to the Deck

Most of chapter 9 is about a new roof. Section R908 of the International Residential Code (IRC) is about the next roof. It sets what you are allowed to do when the covering wears out and it is time to reroof. The core question is whether you can lay new material over the old, or have to strip the roof down to the deck first.

What R908 requires

Before anything goes back on, R908.2 asks whether the structure can carry the new roof. A covering heavier than the original triggers a load check. Then R908.3 draws the line between a recover (new covering over old) and a full replacement. A recover is the cheaper option, but the code bans it in several cases:

A roof recover shall not be permitted where the existing roof has two or more applications of any type of roof covering.

You also tear off down to the deck when the existing deck is water-soaked or deteriorated. Same when the current roof is wood shake, slate, clay or concrete tile, or asbestos-cement. In plain terms: you get at most two layers of asphalt shingles before the next reroof has to be a tear-off. You generally cannot leave old tile or shake in place under a new roof. There are narrow exceptions, such as metal panels or tile laid over an existing wood-shake roof, but do not plan around them.

What it means for an Arizona tile roof

For example, most custom homes across the Valley wear concrete or clay tile. R908 means a tile reroof is almost always a strip to the deck. That is not wasted work here. On an Arizona tile roof the tile is a rain and sun screen, and the underlayment beneath it is the actual waterproof layer. Heat and ultraviolet cook that underlayment from below and above, so it often fails decades before the tile does. A typical Valley reroof lifts and stacks the existing tile, tears off the old underlayment, installs a new high-temperature membrane, and relays the same tile. While the deck is open, the crew redoes the flashing and checks the attic ventilation, because those are far easier to fix with the tile off. It is also the natural moment to step up to a cool roof tile or coating, since the tile is already off and stacked. A reroof needs its own permit in every Valley jurisdiction.

Edition note and related rules

The recover-versus-replacement rules and the two-layer limit in R908 read the same in the 2018, 2021, and 2024 IRC. Confirm the edition your city enforces on the Arizona building code editions by city page. Reroofing pulls in the covering rules of R905, the flashing of R903, and the framing capacity set by R802. The truss or rafter design fixes how much weight the roof can carry. The section text is on the ICC site: 2021 IRC R908 on codes.iccsafe.org.