Built‑up roofing repair and replacement in Phoenix

Through the 1950s, 60s and 70s, built-up roofing was the standard flat roof across Phoenix, Tempe and much of the older East and West Valley. Crews mopped hot asphalt between layers of felt, three or four plies deep, and spread gravel on top to protect it from sun. Done well, it was a tough roof with redundant layers, and some are still in service today after one or two rebuilds.

The trouble is age and heat. Asphalt slowly loses its volatile oils in the sun, and on a Valley roof that process runs fast. As the top plies dry, they shrink and crack, gravel loosens, and the layers below start taking the abuse. Many of these roofs have also been patched for decades with mismatched materials, so part of our job is figuring out which repairs to keep and which to undo. Roof cement smeared over cracks, rolled roofing laid on top of gravel, and coatings over wet plies are the usual suspects we find on these older homes.

Small problems, like a split at a parapet or a single blister, can be cut out and rebuilt with new felt and asphalt, then re-graveled or coated to match. When the surface is aging but the plies below are still dry and firmly attached, resurfacing is an option: we clean and repair the roof, then apply a new reflective cap or coating to shield it from sun. That can buy years at a fraction of replacement cost.

When core samples show moisture between plies over large areas, or the roof has already been resurfaced several times, a full tear-off is the honest answer. Stacking another layer on a wet roof traps water against the deck. At that point we rebuild the built-up system from the deck up, or talk through switching to a modified bitumen roof or foam, depending on the building.

A new built-up roof starts with a sound deck, then a base sheet fastened down, then multiple plies of fiberglass felt set in asphalt or cold-process adhesive. We build slope where needed with tapered insulation so water reaches the scuppers, and we flash every parapet, curb and penetration with new metal and reinforced plies. Gravel or a reflective coating goes on top.

Traditional dark gravel works, but the roof under it still runs hot. Many Valley owners now choose a white reflective coating or a light-colored granule cap instead, which keeps surface temperatures lower and slows aging of the asphalt. If you are comparing the cost of rebuilding against other systems, our flat roof replacement page lays out the main options side by side.

Drainage needs fixing during any rebuild. Old built-up roofs often have small scuppers clogged by decades of gravel, and their low spots show as darker rings where water has sat. We enlarge or reset scupper boxes and tie in new metal so the new roof sheds water quickly, which matters more during a monsoon downpour than any other detail. Clearing gravel guards and adding a scupper and canale fix where needed is part of that work.