Flat roof repair and installation in Horsham and nearby

Where flat roofs show up, and why they leak

On a house around here, the flat part is usually not the main roof. It is the porch roof, the back kitchen addition, a shed dormer, a garage, or the whole roof on a city row home. They are called flat, but a good one has a slight pitch so water drains toward a gutter, scupper or drain.

A pitched shingle roof sheds water in seconds. A flat roof has to hold it out with one continuous waterproof sheet, so it lives or dies on its seams, its edges, and how well it drains. The common failures:

• Ponding water. Low spots that hold water for days after rain. Sun and freeze-thaw cycles wear the membrane fastest right there.
• Open seams. Where two sheets of membrane overlap. Glued or torched seams let go with age and movement.
• Flashing where the flat roof meets a wall. The most common leak on porch roofs and additions: the membrane has to turn up the wall and be covered by siding or metal, and that joint opens up.
• Penetrations. Vent pipes, exhaust fans, skylights and AC curbs cut through the roof and each one needs its own seal.
• Blisters and cracks. Bubbles in modified bitumen or a cracked, chalky surface on older roofs mean the material is near the end.

Looking after a flat roof yourself

Most flat roofs can be seen from an upstairs window, which makes them easier to keep an eye on than a steep roof. Twice a year, and after big storms:

1. Check the drainage. Look a day or two after rain. Standing water that is still there means a clogged drain or scupper, or a low spot. Clearing leaves and debris from the drain is the cheapest flat roof repair there is.
2. Look along the wall line. Where the roof turns up against the house, look for membrane pulling away, gaps behind the metal, or cracked sealant.
3. Look at the seams and the surface. Lifted edges, bubbles, splits, or a surface that has gone cracked and chalky. Take a photo so you can compare next time.
4. Keep traffic off it. Flat roofs are not decks. Furniture, grills and foot traffic wear through membranes. If you have to walk on it, walk softly and stay off it in hot weather when the surface is soft.

Do not use tar on a rubber roof: Asphalt-based roof cement and tar will damage an EPDM rubber roof and make a proper repair harder. If you need a stopgap on EPDM before we get there, a piece of plastic weighted down is safer than a can of patch.

Repair it or replace it?

A flat roof is a good candidate for repair when the leak is in one place, like a seam, a pipe, or the wall flashing, and the rest of the membrane is still flexible and sound. A patch done with the right material for that roof will hold.

It is time to replace when the leaks keep moving around, the surface is cracked or blistered all over, or the boards underneath feel soft when you step on them. Wet insulation and rotted decking under a flat roof do not dry out on their own. Our usual rule applies: once repairs would cost more than about 30% of a new roof, put the money toward replacement. If the flat section is part of a bigger job, it often makes sense to do it along with a roof replacement on the main house.

EPDM rubber or modified bitumen: which one?

• EPDM (rubber). Large sheets of synthetic rubber, usually black, with few seams. Stays flexible in cold weather and is easy to patch. A common choice for additions, garages and bigger flat areas.
• Modified bitumen. Asphalt-based rolls, often with a granule surface like a shingle. Tough underfoot and well suited to porch roofs and smaller areas that tie into a shingle roof.

Both work well when they are installed with good drainage and proper flashing; the details matter more than the brand of membrane. We will recommend one based on the size of the roof, how it drains, and what it joins up to. For flat roofs on businesses and multi-unit buildings, see commercial roofing. For a leak on a city row home, see emergency roof repair in Philadelphia.

What it usually costs

A patch at one seam or pipe is at the low end. Rebuilding wall flashing, fixing a low spot, or replacing wet decking and insulation costs more, and a new flat roof depends mostly on its size.

• Flat Roof Repair: $350 – $1,800
• Flat Roof Installation: $4,000 – $15,000
• Roof Repair: $350 – $2,500

Questions we get asked

How much does flat roof repair cost?

Most flat roof repairs we do run $350 to $1,800. A patch at one seam or vent pipe is at the low end; wall flashing, drainage fixes and wet decking cost more. A new flat roof typically runs $4,000 to $15,000, mostly depending on size.

Is standing water on a flat roof a problem?

Some water right after rain is normal. Water still sitting there a day or two later means a clogged drain or a low spot, and the membrane wears out fastest there. Clear the drain first; if it still ponds, the low spot can be built up or a drain added.

What flat roof systems do you install?

We install EPDM rubber and modified bitumen, the two systems most common on homes and small buildings around here. We recommend one based on the roof size, drainage, and what it joins up to.

Can I put roof cement on my rubber roof?

No. Asphalt-based roof cement and tar damage EPDM rubber and make a proper repair harder later. A rubber roof needs EPDM-compatible patch materials.

Why does my porch roof leak where it meets the house?

That joint is the most common flat roof leak we see. The membrane has to turn up the wall and be covered by siding or metal flashing, and that seal opens up over time. Fixing it usually means opening up the bottom of the siding and reflashing the joint properly, not adding more caulk.

Should I repair or replace my flat roof?

Repair it if the leak is in one spot and the rest of the membrane is sound. Replace it if leaks keep appearing in new places, the surface is cracked or blistered all over, or the deck feels soft. We will show you photos of what we find.

Related pages

• Commercial Roofing: Roof repair and replacement for small commercial buildings, offices and multi-unit properties.
• Emergency Roof Repair in Philadelphia: Emergency leak and storm response for Philadelphia row homes and twins.
• Roof Repair: Leaks, missing shingles, flashing and vents. We fix the problem and tell you honestly how much life the roof has left.
• Roof Replacement: Full tear-off and new roof when repairs stop making sense. Written, line-item estimate before anything starts.
• Skylights: Leaking skylight, or want a new one? Most skylight leaks are flashing, not the glass.
• Roof Inspection: A free, top-to-bottom look at your roof with photos, so you know what you actually need before you spend anything.
• Horsham: Home base. Our shop is here.
• Abington: Stone and brick older homes where details matter.
• Lansdale: Twins, singles and older borough homes.
• North Wales: Borough homes and newer developments around it.
• Hatboro: Borough homes and older twins right next door to Horsham.
• Montgomery County: Where we do most of our work, from Horsham out across the county.