Flat & Low-Slope Roofing

The porch roof that keeps leaking is usually not damaged. It is the wrong material.

A large share of the persistent leaks we get called to in Houston are on a low-slope section of an otherwise fine roof. A back porch, a room addition, a carport, a second-storey deck. The homeowner has had it patched twice and it keeps coming back.

Almost always the problem is not the patch. Asphalt shingles are a water-shedding material. They rely on gravity moving water off them quickly, and they overlap rather than seal. Below roughly a 2:12 pitch, water does not move fast enough, it sits, wind pushes it back up under the courses, and it gets in. Manufacturers say so on the wrapper. Plenty of roofs in this city were built ignoring it.

The pitch rule. Above 4:12, shingles are fine. Between 2:12 and 4:12, shingles are permitted only with a doubled underlayment and specific detailing, and many are installed here without it. Below 2:12, shingles do not belong at all, and no amount of sealant makes them belong.

What goes on a low-slope roof instead

Modified bitumen

Asphalt reinforced with a polymer, in rolled sheets, torched or self-adhered. The seams are fused rather than overlapped, so it is a sealed membrane rather than a shedding surface. It is the workhorse for small residential low-slope areas in Houston, it is repairable, and it handles standing water far better than anything shingle-based.

TPO

A single-ply reflective membrane, heat-welded at the seams. White, so it reflects rather than absorbs, which matters over a room you are trying to cool. Excellent on larger flat areas. Its weakness is punctures, so it is a poor choice where people will be walking on it regularly without a walkway pad.

Standing seam metal

Works down to low pitches and looks intentional on a porch or a carport rather than like a patch. More on metal here.

Why flat roofs fail in Houston specifically

Ponding. A flat roof is never truly flat, it is sloped to a drain. When the deck sags or the drain blocks, water sits. Standing water finds every weakness, and it is heavy, which makes the sag worse.
Drain and scupper blockage. Leaves and pine needles, and in this city that is a twice-yearly job, not an annual one.
UV. A dark membrane in full Houston sun runs extremely hot and ages fast. Reflective coatings are not cosmetic here, they extend the life of the roof.
The transition detail. Where the low-slope section meets the main shingle roof or a wall. This is where most of them actually leak, and it is the detail a patch never addresses.
Foot traffic. HVAC sitting on a flat roof means technicians walking on it. Every service visit is a puncture risk without a walkway.

What we do

Establish the pitch, because that decides whether this is a repair or a re-cover with the correct system.
Check the drainage and whether the deck has sagged. Ponding on a sagging deck is a structural conversation, not a roofing one, and we will say so.
Inspect every seam, every termination and the transition into the main roof.
Repair a sound system, or re-cover with modified bitumen, TPO or metal where the existing material was never right for the pitch.
Sort the drainage out, because putting a new membrane over a blocked drain buys you a couple of years.

What it costs, and how you can check

Every job on this page is priced Cost Plus. You see the supplier invoice for the materials, the crew hours at our published rate, the permit and disposal at what they actually cost, and one service fee of 20 to 30 percent set by job complexity and locked before anything starts. There is no second number and no change order conversation after the fact. The full breakdown is here.

Common Questions

Why does my porch roof keep leaking after repairs?

Most commonly because it is shingled at a pitch too shallow for shingles. Water sits, wind drives it back under the courses, and it gets in. Repairs to the shingles cannot fix a material that does not belong at that pitch.

How long does a flat roof last in Houston?

Modified bitumen and TPO both do well here when the drainage works and the surface is coated. Ponding water and a blocked drain are what shorten them, far more than age.

Can you coat my flat roof instead of replacing it?

If the membrane is sound and the seams are intact, a reflective coating is a genuinely good value move and it lowers the surface temperature substantially. Over a failing membrane it is money spent to delay the same job.

Is standing water on a flat roof normal?

Water still sitting forty eight hours after rain is not. It means the slope or the drainage has failed, and it needs sorting before any new surface goes on.

Get a Cost Plus quote for flat & low-slope roofing

Free inspection, photographed and written up, with a line-by-line quote inside one business day.

Get My Free Inspection

Or call (281) 305-8669