Do you do shingle roofs?

No. Shingles and steep-slope coverings are a roofer's trade and we do not take them on, and you get told that on the phone. What we do is repair to flat and low-slope membrane roofs — EPDM seams, modified bitumen patching, flashings, penetrations and drains — plus all of the roofline, meaning fascia, soffit, trim, flashing, gutters and downspouts. If a shingle roof is the problem, that is a roofer first; the roofline and interior work can follow it.

My flat roof only leaks sometimes, not every time it rains. Why?

That is normal behavior for a low-slope roof and it is why these leaks go unfound for so long. Water that gets through a seam does not fall straight into the room — it travels between the membrane and the deck, or through the insulation, until it reaches a joint, a fastener or a light fitting and comes through there. So whether you see anything depends on how much rain fell, from which direction, and whether the water reached the exit before it stopped. A leak that lags a day behind the weather is holding water somewhere, and where it is holding it matters more than where it is dripping.

There is water standing on my flat roof. How urgent is that?

Urgent, and for the weight rather than the leak. Water runs about five and a quarter pounds per square foot per inch of depth, so an inch across a twenty-by-thirty-foot roof is over three thousand pounds sitting on the building, and it does not go anywhere by itself. Standing water also finds every weakness it touches and accelerates the aging of the membrane under it. The first question is always whether a drain is blocked, because that is cheap and common. If the drains are clear and it still ponds, the roof has lost its fall or the deck has deflected, and that is a structural engineer's question — which we refer rather than patch over.

Can an EPDM roof be patched, or does the whole thing have to come off?

Patched, in most cases. The field of an EPDM sheet is an inert piece of rubber that long outlives the details attached to it, so what fails is seams, laps, terminations and penetrations. A repair means cleaning back to sound membrane and bonding a new cover strip over the failure — the invoiced job behind this article was a hundred and ten linear feet of seam on a commercial unit, and the field of the roof was never touched. Where it genuinely has reached the end is when the insulation underneath is saturated or the deck has gone soft, because then a watertight patch sits on top of a problem it cannot reach. You get told that rather than sold the patch.

Will a repair void my roof warranty?

It can, and it is worth checking before anybody starts. Commercial single-ply roofs are often installed under a manufacturer's system warranty that requires work to be done by one of their certified installers, and a repair by anybody else can void the remaining cover. We are not a certified installer for those systems and do not pretend to be, so if your roof is still inside a system warranty the right advice is often to call the original installer — and that is what we will tell you. We do not issue a warranty on a repair either, because sealing a seam is a repair and not a roof.

A Flat Roof Leak Is a Weight Problem First: Where Low-Slope Roofs Actually Fail

Q: What counts as a low-slope roof?

Anything under roughly two inches of rise per foot of run. That is the threshold below which asphalt shingles are no longer permitted and the roof has to be a membrane system instead. In practice it means anything that looks flat: a commercial roof, a flat porch or addition, a garage roof, the top of a dormer. It does not have to be literally level, and a well-built one never is, because it needs enough fall to get water to a drain.

Q: Do you work on houses or only commercial buildings?

Both, with one honest caveat about the record. Flat porch, addition, dormer and garage roofs on houses are in scope and are the same work at a smaller scale. But the invoiced low-slope work in our records is commercial and light-commercial — a retail unit and a realty company's buildings — so when we say the work has been done and paid for, that is the work we are talking about. We are not going to imply a domestic track record we do not have yet.

Q: Can you torch on a bitumen patch?

No, and it is not a scheduling problem or something that can be arranged for the right price. Open-flame roofing is one of the leading causes of fires on construction and repair jobs, it requires a hot-work permit and a fire watch kept after the crew has left, and the risk is carried by your building rather than by whoever is holding the torch. Modified bitumen is available in self-adhered form, that is what we have used on the jobs here, and it does the same job without putting a flame on a roof deck with twenty years of dry felt under it.

A pitched roof sheds water. A low-slope roof contains it.

Almost everything that is confusing about a flat roof follows from that one difference, including the two questions people actually ask: why does it only leak sometimes, and why does the stain appear nowhere near the hole.

Shingles overlap. Water is moving off them within seconds, so a small fault produces a drip more or less where the fault is. A membrane roof is one continuous surface holding water that has nowhere urgent to be. A small fault in it produces nothing at all for a year, and then produces a ceiling.

“Low slope” is a definition rather than a feeling, incidentally: under about two inches of rise per foot of run. That is the threshold below which asphalt shingles are no longer permitted and the roof has to be a membrane system instead. In practice it means anything that looks flat — a commercial roof, a garage, a flat porch or addition, the top of a dormer.

They almost never fail in the middle

This is the most useful thing to know about a flat roof, because it changes what a repair costs.

The field of an EPDM sheet is an inert piece of rubber and it long outlives everything attached to it. What fails is every place the membrane stops or is interrupted: seams and laps, terminations at a parapet or a wall, pipe boots, curbs around a rooftop unit, and drains.

The invoiced job behind this article is a good illustration rather than an exception. A commercial unit here needed a hundred and ten linear feet of failed EPDM seam repaired, plus the drains cleared — two thousand and fifty dollars, and nobody touched the field of the roof. On a separate commercial property we patched two failed areas of self-adhered modified bitumen on an upper roof, and raised a dead-flat lower roof on tapered sleepers to re-cover that section in one-piece 60 mil EPDM so it would actually drain.

So when someone looks at a leaking flat roof and quotes you for the whole thing, the fair question is which of those two situations you are in — a failed detail on a sound roof, or a roof whose insulation and deck are already wet.

Standing water is a weight problem before it is a leak

This is the part that gets under-rated, and it is worth doing the arithmetic because it is not intuitive.

Water weighs about five and a quarter pounds per square foot for every inch of depth. So an inch of standing water across a modest twenty-by-thirty-foot flat roof is a little over three thousand pounds. It sits there. It does not drain itself. And it gets heavier every time it rains.

Standing water also finds every weakness it is in contact with, and it accelerates the aging of the membrane underneath it. So ponding is not a cosmetic complaint about a roof that looks untidy — it is the roof telling you something.

The first question is always whether a drain is blocked, because that is both the most common cause and the cheapest. A ball, a bag, or one season of leaves over a drain will do it. If the drains are clear and it still ponds, then the roof has lost its fall or the deck has deflected, and that is a structural engineer's question. We refer that out, and we do not treat the referral as a lost sale — nobody should be offering you an opinion on what your building can carry unless they are qualified to give one.

Why it only leaks sometimes

Because water that gets through a seam does not fall straight into the room below. It travels — between the membrane and the deck, or through the insulation — until it reaches a joint, a fastener or a light fitting, and it comes through there.

So whether you see anything at all depends on how much rain fell, from which direction, and whether the water reached an exit before it ran out. Two useful observations you can make yourself:

A leak that starts with the rain suggests an open path at a seam or a penetration.
A leak that lags hours or days behind the weather means water is being held somewhere and tracking. Where it is being held matters far more than where it is dripping.

Tell whoever comes out which of those two you have. It genuinely changes where they look first.

What we will not do, and why

We should be as clear about this as about the work itself.

No shingles and no steep slopes. That is a roofer's trade and we do not take it on. You get told on the phone rather than after a visit. What we do nearby is the roofline — fascia, soffit, trim, flashing, gutters and downspouts — and repair to flat and low-slope membrane.

No stripping and re-covering a whole building. We repair, and we will rebuild fall across a defined section. A building that needs its covering renewed end to end needs a roofing contractor and a warranty we cannot issue.

No torch-applied work, ever. Not a scheduling problem and not something that can be arranged for the right price. Open-flame roofing is one of the leading causes of fires on repair jobs, it requires a hot-work permit and a fire watch kept after the crew has left, and the risk is carried by your building rather than by whoever is holding the torch. Modified bitumen comes in self-adhered form, that is what we have used, and it does the same job without putting a flame on a deck with twenty years of dry felt under it.

Pre-1990 built-up roofing is treated as asbestos-containing until sampled. Old roofing felts and mastics can contain it. We do not cut, scrape, grind or disturb it, and asbestos work is excluded here.

And no roof warranty. Sealing a seam is a repair, it is not a roof, and it does not carry a roof warranty — that is our own quote wording and we are not softening it here. Related: if your membrane is still inside a manufacturer's system warranty, a repair by anyone who is not one of their certified installers can void what is left of it. We are not a certified installer for those systems. If that is your situation, the right advice is often to call the original installer, and that is what we will tell you.

One honest caveat about our record

The invoiced low-slope work in our records is commercial and light-commercial — a retail unit and a realty company's buildings. Flat porch, addition, garage and dormer roofs on houses are in scope and are the same work at a smaller scale, but we have not yet invoiced a domestic one, and it would be overstating things to imply a track record we do not have.

Before anyone comes out

Photograph the inside of the leak and get the date in the frame. On a low-slope roof the inside evidence is often the only usable record of how fast it is getting worse.
Do not go up there. A wet membrane is genuinely slippery, snow hides everything including the edge, and a roof with water standing on it may already be carrying more than it should.
Note the timing — with the rain, or lagging behind it.
If you can safely see the drains from a window or a hatch, check whether something is sitting on one.
If this is a commercial tenancy, find out who owns the roof. It is in the lease, it takes ten minutes, and it saves two weeks of the wrong person collecting quotes.

Want it looked at? Send the inside photographs and tell us whether the leak starts with the rain or lags behind it. Somebody gets on the roof safely, finds the water path rather than the stain, and puts a fixed price in writing with the exclusions on it. Coming out is free and there is no trip charge. Low-slope roof repair · Get in touch.