Somebody has already been up there. They sealed around it, maybe twice, maybe three times, and the stain on the ceiling came back with the next hard rain. That is the most common call we take, and it almost always means the same thing: the water was never coming from where the last person assumed it was.
A second patch on a wrong diagnosis fails exactly like the first one did. Our leak diagnostic asks six questions about where the water shows up and when, and it will usually narrow this to one or two causes before anybody climbs a ladder.
Sealant is a repair for one thing, and that is a joint that has opened up and is otherwise correctly built. It is not a repair for water that is getting in above the skylight and running down to it, and it is not a repair for a curb that has rotted underneath the flashing. When you put a bead of caulk over a problem that is structural, you get a few dry weeks and then the same stain.
There is a second reason it fails, and it is worse. Sealant applied over the top of flashing often traps water behind it instead of keeping water out. The roof was designed to shed water in layers, each one lapping over the one below. A bead of caulk across those layers dams the path. Now the water that used to run out has nowhere to go, so it sits, and it finds the first gap in the wood.
This is why the third visit from the same person is rarely the one that fixes it. Nothing has been diagnosed yet. The same assumption is being applied harder.
It is the unit. The seal between the panes has failed, a gasket has perished, the frame has cracked at a corner, or the operator on a venting unit no longer closes it tight. On an older acrylic dome, the plastic itself goes brittle and crazes, and a hairline you cannot see from the ground passes water.
It is the flashing. This is where the skylight meets the roof, and on a pitched roof it should be a proper step flashing kit, woven in course by course. We find sealant where the kit should be more often than we find anything else. On a flat roof it is the base flashing turning up the side of the curb, and the usual failure is that a roof recoat ran over the top of it and sealed the lap shut.
It is the curb. The box the skylight sits on is wood, it is site built on most older New York houses, and once water has been getting into it for a few seasons it goes soft. A soft curb will not hold a fastener and will not hold a straight line for the flashing to sit against. You can put a brand new skylight on a rotted curb and it will leak within the year.
It is not the skylight at all. Water travels. It comes in at a parapet, a coping stone, a chimney, a vent boot or a seam fifteen feet uphill, runs along the underside of the deck, and drops at the first obstruction it meets, which is the framing around your skylight. The skylight is where the water appears. It is not where the water entered.
We start inside, not on the roof, because the inside tells you more than people expect. Where the stain sits relative to the opening, whether the drip is at a corner or along one side, whether the plasterboard is wet high or wet low, and whether there is any staining at all on the skylight frame itself all point in different directions. A unit that is failing wets its own frame. Water arriving from uphill usually does not.
Then we get on the roof and look at the layers in order, from the top of the slope down to the head of the skylight, because that is the direction water travels. We are reading how the roof was built, not just looking at the skylight. On a flat roof we are looking at where the recoat stopped, whether the base flashing is still a separate layer or has been glued into the field, and how the water drains across the area.
We open nothing and remove nothing on that first visit unless you ask us to. The point of the assessment is to leave knowing which of the four it is, so the number we give you afterwards is for work that will actually end the leak.
The assessment is free, and that includes a leak somebody else has already been paid to fix.
Pouring a bucket of water over it tells you very little. It wets a small area at low pressure for a few seconds, which is nothing like a wind driven rain that pushes water sideways and uphill for an hour. Plenty of skylights that pass a bucket leak in a storm.
A hose test is better but it has to be done in the right order, starting low and working up the slope, one zone at a time, with somebody inside watching. Done in the wrong order it tells you nothing, because once water is inside you cannot tell which zone let it in. We also will not hose test fresh materials, because the materials we install need time to cure and wetting them early is how you create the next problem.
Watching it rain is genuinely useful and it costs nothing. If you can be in the room during the next hard rain and note the time the drip starts relative to when the rain started, which direction the wind was blowing, and exactly where the first drop lands, that is real evidence. A leak that only appears when the wind is from one quarter is a flashing or a wall problem. A leak that starts within a minute of the rain and stops with it is usually the unit.
If the curb is sound and the problem is the flashing, it is a repair, and it is the kind of repair that holds for decades when it is built properly rather than sealed.
If the unit itself has failed and it is a modern VELUX in a standard size, the honest answer is often that replacing it costs less than chasing it. A full replacement on an existing sound curb starts at $2,079 installed, and that is a complete system with the solar shade and remote, NYC sales tax included, backed by our 10 year No Leak Warranty.
If the curb has gone soft, it has to be rebuilt whatever else happens, and that is quoted after we have seen it because the amount of rot is not knowable from a photo. We build flat roof curbs at five and a half inches, above the four inch code minimum, and we build them sloped, because a curb that sheds is a curb that stops needing attention.
If the water is not coming from the skylight, we will tell you that, and we will tell you plainly that the work you need is roofing work rather than ours. We would rather lose the job than sell you a skylight that was never the problem.
Every honest answer to a repeat leak is the same shape: the price depends on which of the four causes it is, and there is no way to know which from the outside. A company that quotes you a repair number off a photo is quoting the cheapest of the four and will find the rest once the roof is open.
That is the whole reason we do the assessment for free and before we quote. The number you get afterwards is attached to a specific failure we found, not to a guess, and it does not move halfway through the job.
What does move the number is the things we can see once we are there: whether the curb can be kept, how many units are involved, how hard the roof is to reach, and whether the roof around the skylight is near the end of its life anyway. On a building where the roof is due, doing the skylight at the same time is almost always cheaper than doing it twice.
In a co-op, a condo or a rental, the skylight over your apartment is very often a common element even though the water is landing on your ceiling. That changes who authorises the work and who pays for it, and it is the reason a lot of repeat leaks go unfixed for years while nobody takes responsibility.
We deal with managing agents and boards regularly and we can write the assessment so it is usable at a board meeting, with the cause stated plainly and the options separated out. If you are a board member or an agent, our page for boards and managing agents covers how we handle approvals, access, insurance certificates and alteration agreements.
If you are the resident and you do not control the roof, we can still come and diagnose it from inside, and that report is usually what finally moves the building to act.
Photographs of the ceiling stain, taken with the light on, and one wider shot showing where the skylight sits in the room. If the skylight has a data plate on the inside of the frame, a clear photo of it tells us the exact model and age.
Anything you know about what was done before. Who worked on it, roughly when, and what they said they did. If there is a receipt or an invoice with a description on it, that is worth more than a memory.
If the skylight is reachable from inside and safe to reach, a photo looking up at the glass or dome from directly underneath will often show a failed seal straight away. Do not go on the roof for us. We will do that part.
Send them through the contact page or call (718) 646-7053 and we will tell you what we think before we come, so you are not waiting on a visit to get a first opinion.
Related reading. If the water is getting in around the unit rather than through it, skylight resealing explains when a reseal of the perimeter is the repair that actually solves it, and when it is money spent twice.
Almost always the direction the water is travelling. Sealant assumes the water is entering at the joint it is being applied to. If the water is entering uphill of the skylight, or soaking into a soft curb underneath the flashing, the sealant is in the wrong place and it will fail again on the same schedule. It is not usually carelessness. It is a diagnosis that was never made.
Yes, and it is more common than most people expect. Water that enters at a parapet, a coping, a chimney or a seam further up the roof runs along the underside of the deck until something stops it, and the framed opening around a skylight is a very effective something. The skylight is where the water shows up. That is not the same as where it got in.
No. If the curb is sound and the unit is intact, the right repair is usually the flashing, done properly rather than sealed. Replacement becomes the sensible answer when the unit itself has failed, when it is an old acrylic dome that has gone brittle, or when the curb underneath has rotted and has to be rebuilt anyway.
Most of them we can name in one visit of under an hour. The ones that take longer are the travelling leaks, where the entry point is somewhere else on the roof, and those sometimes need a staged hose test on a dry day with somebody inside watching. We will tell you at the end of the first visit if that is where yours is heading.
No. The assessment is free whether the skylight is one of ours, somebody else's, or something that has been patched four times. We would rather look at it properly than have you guess again.
Two separate things, and it is worth keeping them apart. A unit still inside its manufacturer warranty keeps that warranty, and we do not affect it. Our own 10 year No Leak Warranty covers the work our crews carry out, so if we rebuild the flashing it covers the flashing, and if we replace the unit it covers the installation. What it cannot cover is the part of the roof somebody else built and we did not touch.
A stain means water has already been in the ceiling, and the damage that matters is happening in the framing where you cannot see it. Wet timber around an opening loses its grip on fasteners long before anything looks dramatic from below. It does not need to be an emergency, but it does need to be looked at before the winter rather than after it.