Flat roof repair, coating and replacement
Flat roofs are everywhere in the Valley: on commercial buildings, patios, additions and Pueblo-style homes. Good drainage and a healthy surface are what keep them dry.
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The short answer
Flat roofs aren't completely flat; they're built with a slight slope to drain. Most flat-roof leaks start at seams, flashing, roof drains and scuppers, or where water ponds. Common flat-roof systems in Arizona include spray foam, modified bitumen and elastomeric-coated roofs.
Flat roof systems we work on
The right system depends on the building, the existing roof, and your budget.
- Spray polyurethane foam: seamless and insulating
- Modified bitumen: durable rolled roofing with a protective cap sheet
- Elastomeric coatings: reflective protection over sound roofs
- Repairs to seams, drains, scuppers, parapets and flashing
Ponding water is a warning sign
Water that stands on a flat roof for more than a couple of days after rain speeds up wear and finds its way into seams. It also adds weight and collects dirt that cuts reflectivity. We can improve drainage, for example by adding tapered foam or clearing and repairing drains, as part of a repair or replacement.
How a flat roof drains
A flat roof moves water with a gentle slope toward its exits. Those exits are either roof drains, which carry water down through pipes inside the building, or scuppers, which are openings through the parapet wall that send water to a downspout or off the edge.
Crickets, small sloped ridges built behind AC units, chimneys and along walls, steer water around obstacles toward the drains. When any part of this path settles or clogs, water backs up and finds a weak spot.
Parapet walls and scuppers
Many Arizona flat roofs are surrounded by parapets, the short walls that rise above the roof line. They hide equipment and give homes their Pueblo look, but every place where the roof meets the wall needs flashing that climbs up the wall and is sealed at the top.
Common leak points include cracked stucco on parapet tops, failed caps, and scuppers whose flashing has pulled loose. A clogged scupper during a monsoon downpour can flood the roof edge in minutes, so keeping them clear is one of the easiest ways to prevent leaks.
Modified bitumen explained
Modified bitumen is an asphalt-based roofing sold in rolls and reinforced with polyester or fiberglass. It's installed in overlapping layers, with the seams heat-welded or adhered. The top cap sheet is usually covered in granules for UV protection, and a reflective coating can be added to keep it cooler. It handles foot traffic well, which is why it's common on commercial roofs.
Rooftop equipment and penetrations
AC units, evaporative coolers, vent pipes, skylights and solar mounts all pass through or sit on a flat roof. Each needs a sealed curb or boot, and evaporative cooler drips and service foot traffic wear the surface around them. Solar works well on flat roofs, but the roof should be in good shape before panels go on.
Flat roof maintenance checklist
Do this before monsoon season and after big storms.
- Clear leaves, dust and debris from drains and scuppers
- Look for water that remains two days after rain
- Check parapet caps and stucco for cracks
- Inspect flashing around AC units, vents and skylights
- Look for blisters, cracks, open seams or exposed foam
- Schedule a roof inspection once a year
Repair, recoat or replace?
If the roof is dry and mostly sound, targeted repairs plus a fresh coating can buy many more years. If moisture has soaked the insulation or the surface has failed across large areas, replacement is the better value. For cost factors on each, see the Roofing Cost Guide.
Related services
Spray Foam Roofing
Our featured system: seamless, insulating, renewable roofs.
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Foam Roofing
Seamless, insulating flat roofs: install, repair, recoat.
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Elastomeric Coatings
Reflective, waterproof coatings for flat roofs.
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Commercial Roofing
Flat roofs, foam, coatings and maintenance for businesses.
Learn moreFrequently asked questions
Still have a question? Call the office at 602-548-3770, Monday to Friday, 7 am to 5 pm.
Why do flat roofs leak?
Common causes are failed seams, worn flashing at parapet walls and penetrations, clogged drains and scuppers, ponding water, and coatings that have worn thin from UV exposure.
How long does a flat roof last in Arizona?
It depends on the system: modified bitumen often lasts around 10–20 years, while a well-maintained foam roof can last 20+ years with periodic recoating.
Is ponding water on a flat roof normal?
A little water that evaporates within a day or two is common. Water that stands longer can accelerate wear and should be addressed by improving drainage.
Can a flat roof be converted to foam?
Often, yes. If the existing roof is dry and sound, foam may be applied over it; otherwise the old roof is removed first.
How often should a flat roof be inspected?
At least once a year, plus after major storms. Commercial flat roofs benefit from inspections in both spring and fall.
What is a scupper?
A scupper is an opening through a parapet wall that lets water drain off a flat roof, usually into a downspout. Its flashing must be sealed to the roof, and it needs to stay clear of debris.
What is a parapet wall?
It's the short wall that extends above the roof surface around the edge of many flat roofs. The joint where the roof meets the parapet, and the cap on top, are common leak points.
What is a cricket on a flat roof?
A cricket is a small built-up ridge that directs water around an obstacle, such as an AC unit or chimney, and toward a drain. It prevents water from pooling behind the obstacle.
Why does my patio roof leak?
Flat patio roofs often leak where they tie into the main house, at worn coatings, or where water ponds because the slope is too shallow. The connection to the main roof needs careful flashing.
Can my AC unit cause roof leaks?
Yes. Units sit on curbs that must be sealed, condensation and cooler drips wear the roof, and service visits add foot traffic. We check these areas closely during inspections.
Can solar panels go on a flat roof?
Yes. Panels are mounted on racks that are either sealed into the roof or weighted, depending on the design. Make sure the roof is in good condition first so panels don't need to be removed for repairs.
How much does flat roof work cost?
Every roof is different, and price depends on size, the system, drainage work, repairs and access. See our Roofing Cost Guide at /resources/roofing-cost-guide/, or call 602-548-3770. If we don't answer, leave a message and we'll return your call within 24 hours.
Let's take a look at your roof.
Call the office at 602-548-3770 to schedule an estimate, Monday to Friday, 7 am to 5 pm. If we don't answer, leave a message and we'll return your call within 24 hours.