Why does water sit on a flat roof?
A flat or low-slope roof has little fall, so water that does not reach a drain stays on the surface. Ponding can come from a blocked drain, a sagged section of the deck or a membrane that has settled, and all three need a repair rather than more sealant.
A small amount of standing water after a heavy rain is common on a low-slope roof, but water that stays for days is a sign of poor drainage. It adds weight, it soaks the seams at the low spot and it speeds up the wear of the membrane.
A crew checks whether the ponding is caused by a blocked drain, a low spot in the deck or a membrane that has moved. The cause decides the repair, and the crew says which one it has found.
Are seams the most common flat roof leak?
Seams and laps are among the most common leak points on a flat roof, because they are joints in a material that moves with the sun and the wind. A seam that has opened at one spot often shows the same wear along its length.
A crew checks the seams by walking them and looking for lifted edges, bubbles and gaps. The seam at the edge of the roof and the seam over a drain are checked with extra care, because water collects at both.
Resealing a seam works only when the surface is clean and dry and the old material is sound. A crew cleans the seam and tests it before it applies new sealant or patch material.
Can a flat roof section be repaired rather than replaced?
Often yes. A flat roof with a sound membrane and a few failed seams, drains or patches can be repaired section by section. A membrane that is brittle across most of the surface or that has lost its adhesion is closer to a replacement, and the crew says so.
A repair is judged by how much of the membrane is still flexible and bonded. A crew lifts a small area to test the bond and the thickness, and it records what it finds. Where the membrane is failing in many places, the repairs will not hold for long.
The homeowner should ask for the findings in writing, with the sections marked on a sketch or a photograph. That record is the basis for deciding between repair and replacement later.
What should I do if water is pooling on my flat roof?
Do not walk into standing water or try to clear a drain from the roof. Note where the water sits, photograph it after the rain and ask for a crew to check the drains and the low spots. Keep the area below clear and check the ceiling for stains.
Standing water can hide a soft spot in the deck and it is slippery. A crew uses the right footing and clears the drain safely, and it reports the depth and extent of the ponding in its note.
If water is coming through a ceiling, move valuables away from the stain and place a container beneath the drip. Report it so the crew can check the drain and the seams that lead to it.
What affects the scope of a flat roof repair?
The scope depends on the area of the section, the number and length of the seams, the drains and the edges, and the condition of the membrane. The price is explained and approved before any work starts, and no figure is printed on this page.
A small section with one drain and two failed seams is a short repair. A large section with several drains, a long parapet and a brittle membrane needs more time and materials, and the crew lists each part separately.
Access matters too. A flat roof reached by a ladder or a hatch is different from one that needs a lift, and the crew plans the access and the safety equipment before it starts.
