Flat Roof Leaks in Las Vegas: Ponding, Seams, Scuppers and Drains
Flat and low-slope roofs usually leak where water collects or where something goes through the roof: a seam, a drain, a vent or a wall edge. A clogged drain or a low spot that holds water after rain is often the cause.
The cause can be found and fixed. Here is what to look for and what the repair involves.
Why flat roofs leak differently
A pitched roof sheds water quickly. A flat or low-slope roof sheds it slowly, and it depends on drains, scuppers or edges to carry water away. When that system does not work, water sits on the roof.
In Las Vegas, flat and low-slope sections are common on modern homes, additions, patio structures and older central-valley houses. Monsoon downpours test every one of them.
Ponding: water that does not leave
Roofers use the term ponding. The National Roofing Contractors Association defines it as water that remains on a roof surface longer than 48 hours after the most recent rain.
Ponding is a warning sign. Standing water finds seams, penetrations and weak spots and leaks through them. Water that sits also adds weight to the roof, and the roof can sag further under each storm, which makes the low spot bigger.
If you have a flat section, check it a day or two after rain. Water still sitting there is the sign.
Scuppers and drains
A scupper is an opening through the edge wall of a flat roof that lets water run off. A drain does the same job through the roof surface. When either one is clogged with leaves, grit or debris, water backs up and pools around it.
A clogged scupper or drain is one of the simplest causes of ponding, and one of the easiest to check from the ground or from a window. Look for water standing near the edge or in a low corner.
Seams, edges and penetrations
Water that pools will find any weak point. On a flat roof, those are seams in the roofing, the flashing where the roof meets a wall or curb, and anything that comes up through the roof, such as vent pipes.
These are the same spots we check on any roof. The difference on a flat roof is that water sits against them instead of running away. We describe the full process in roof leak detection.
How a flat roof leak is found
As with any leak, the stain inside is not always below the entry point. Water can run along the roof deck before it drips. We look at the low spots, the drains and the edges, then the seams and penetrations. If the cause is not clear, controlled water testing can confirm it.
See how we find a roof leak for the steps.
What the repair looks like
If the cause is a clogged drain or scupper, clearing it may stop the ponding. If a seam or penetration has failed, it can be repaired. Where the roof will not drain because of its slope, we can look at correcting the slope where that is feasible.
On roofs that have reached the end of their life, or where ponding is chronic, a new reflective TPO or PVC single-ply membrane can be installed with slope-to-drain detailing, sealed penetrations and watertight flashing at every wall and curb. The seams in these membranes are heat-welded into a continuous surface. See our TPO and PVC roofing page, and our article on flat roof options in Las Vegas.
What to do now
If you suspect a leak on a flat section, take photos of any standing water after rain and of the stain inside. Please do not walk on the roof. Send the photos to (725) 502-3114 and we can tell you what we see.
Frequently Asked Questions
What is ponding?
Ponding is water that stays on a roof longer than 48 hours after rain stops.
Why does my flat roof leak after it rains?
Often because water sits against a seam, a vent or an edge and finds its way in, or because a drain or scupper is blocked.
Can a flat roof leak be repaired without a new roof?
Often, yes. If the cause is a blocked drain, a failed seam or a bad penetration, it can be repaired. A new membrane is for roofs at the end of their life.
Do you install torch-down or spray foam?
No. For flat and low-slope roofs we install reflective TPO or PVC single-ply membrane.
Who do I call?
Call or text photos to (725) 502-3114.