On a flat roof, water should drain off within a day or two after rain. If it sits longer, something is wrong - usually a clogged drain or scupper, a low spot, or a worn roof surface. Standing water speeds up wear and is a common cause of flat roof leaks in Phoenix. All Valley Roofing repairs flat roofs across the Phoenix area, and drains are one of the first things we check.
How water leaves a flat roof
A "flat" roof is not perfectly flat. It has a slight slope that moves water toward a way out:
- Scuppers: openings in the parapet wall that let water run off the edge
- Roof drains: openings in the roof surface that carry water down through pipes
- Gutters and downspouts: on some edges and patio covers
When any of these get blocked, water backs up. On Phoenix roofs, the usual culprits are dust, leaves, palm fronds, bird nests, and debris left behind by storms.
Why standing water is a problem
A little water after a storm is normal. Water that stays more than a day or two causes trouble:
- It wears down the roof surface faster, especially on foam and coated roofs
- It finds small cracks and seams and works its way in
- It adds weight to the roof
- It collects dirt that keeps drains blocked
Phoenix summers make it worse. Heat and sun break down roof surfaces, and standing water does its damage in the spots that are already weak.
Signs your flat roof has a drain problem
From the ground or a ladder, look for:
- Water still sitting a day or two after rain
- Rings of dirt or stains where water has pooled
- Water stains on walls below scuppers
- Debris piled near drains or parapet openings
- Plants or moss growing on the roof
Inside, look for ceiling stains, especially near outside walls and under roof drains.
What flat roof repair involves
Clearing and checking drains
We clear scuppers and drains, check that water can flow through them, and look at the pipes and openings for damage.
Fixing seams and roof openings
Many flat roof leaks start at seams and around roof openings, like vents, pipes, and AC stands. We patch or reseal the bad spots. Our post on TPO roof seams and flashings covers that work for TPO roofs.
Treating low spots
Some roofs have low areas where water always collects. Depending on the roof type, that may mean building up the low area, adding a way for water to get out, or, on foam roofs, adding foam and a new top coat.
Recoating worn areas
Foam and coated roofs need a sound top coat to stand up to water and sun. If the coat is worn near low spots, recoating that area can extend the roof's life. Our post on when a foam roof recoat fails explains when a recoat is not enough.
Everything we find goes in your Free Roof Report with photos, so you can decide what to fix now and what can wait.
Keep drains clear before winter rain
A simple check in the fall can prevent a lot of trouble:
- Clear leaves and debris from scuppers and drains
- Look for cracks around roof openings
- Check for worn coating near low spots
- Make sure downspouts are not blocked at the bottom
If you are not comfortable on the roof, or if the roof is high, have a roofer do it.
FAQ
How long should water sit on a flat roof?
Water should drain within a day or two after rain. If it sits longer, have the roof checked.
Can a clogged scupper cause a leak?
Yes. Blocked water backs up and can find cracks or seams, especially near the parapet.
Do I need a new roof if water ponds?
Not always. Many ponding problems can be fixed by clearing drains or treating low spots. The report shows what your roof needs.
What affects the cost of flat roof repair?
Drains, roof openings, roof size, the roof type, and how much area is worn. Your written quote shows the price.
Get your flat roof checked
All Valley Roofing is based in Tempe and works across the Phoenix area, including Phoenix. See our flat roofing and foam roofing pages, request a Free Roof Report, or contact us.
Next step: Free Roof Report
No cost. No obligation. Yours to keep. Tempe-based All Valley Roofing documents whether you need routine maintenance, localized repair, underlayment work, or a full system. Prefer a leak first? Go to roof repair.