Flat and low slope roofs are a familiar sight in Tucson, often hidden behind a short parapet wall so you cannot see them from the street. Most are covered in sprayed polyurethane foam with a coating on top, or in a rolled membrane. They are not truly flat: they are built with a slight slope so rain runs to drains or to openings in the parapet called scuppers. Most flat roof problems come back to two things: water that does not drain, and a top layer that the sun has worn away.
Common flat roof problems in Tucson
Ponding water
After a monsoon storm, water should leave a flat roof within a day or two. If it sits longer, it softens some coatings, adds weight and finds small cracks. Ponding usually means a low spot, a sagging section of deck, or a clogged scupper or drain.
Clogged scuppers and drains
Leaves, dust and debris build up over the dry months, then block the outlets in the first heavy storm. July averages about 2.21 inches of rain in Tucson, and much of it can fall in a short burst. A blocked scupper can send water over the parapet or back under flashing. Clearing them in spring is one of the cheapest things you can do for a flat roof.
Worn coating and exposed foam
Foam itself is not built to sit in the sun. With about 3,806 sunshine hours a year in Tucson, the coating on top wears thin, and once foam is exposed it starts to break down. See roof coating for recoat details.
Blisters and wet foam
Blisters are bubbles where the foam or coating has separated, often because moisture got trapped. Small dry blisters can be cut out and filled. Large areas of wet foam need to be removed and replaced.
Bird and foot traffic damage
Birds sometimes peck holes in foam, and people walking on the roof to service an air conditioner or cooler can dent or puncture it. Small holes let water into the foam, so they should be sealed before the rain.
Parapet walls and flashing
The joints where the roof meets the parapet wall, and the cap on top of the wall, are common leak points. Cracked stucco on parapets can also let water into the wall and down into the house.
What a flat roof repair involves
A roofer checks how water moves across the roof, clears scuppers and drains, and looks for soft or wet areas. Repairs might include cutting out damaged foam, filling and recoating patches, resealing flashing at walls and rooftop units, or adding foam to build up a low spot so water drains. For a membrane roof, they patch splits and reseal seams.
Older flat roofs
Tucson's housing is old: 52.5% of homes in the city were built before 1980, and 21.6% before 1960. An older flat roof may have been foamed and recoated several times, or covered over an older built-up roof. When layers stack up, moisture can get trapped between them. If the roofer finds wet layers in many areas, a full tear-off and new roof may be better value than another patch. See roof replacement.
How to look after a flat roof
- Clear scuppers, drains and gutters each spring, before monsoon season starts on 15 June.
- Look at the roof after big storms for pooling water and debris.
- Keep foot traffic to a minimum, and ask service techs to use walk pads where they exist.
- Have the coating checked well before bare foam shows.
- Watch the ceiling under the flat roof for new stains.
Common questions
How long should water stand on a flat roof?
Water should drain within about a day or two after rain. Water that stays longer points to a low spot or a blocked drain that a roofer should look at.
Can a foam roof be repaired, or does it need replacing?
Many foam roofs can be repaired by cutting out damaged foam, filling it and recoating. Large areas of wet foam may mean a tear-off is the better choice.
Can I walk on my foam roof?
Light foot traffic is usually fine on a well coated roof, but avoid it when you can. Heels, tools and sharp objects can dent or puncture the foam.