A skylight brings light into an attic bedroom or a dark stair hall, and it is also a square opening cut through the one surface that keeps the weather out. Whether it leaks comes down to how it is flashed.
Quick answer: A skylight is an opening cut into the roof, and only the flashing keeps water out of it. A curb-mounted unit sitting on a raised, step-flashed curb sheds water far better than a low deck-mounted unit leaning on a gasket, especially under West Michigan snow. Quality skylights last 15 to 40 years, but the flashing and the ice and water membrane underneath decide the real number. Caulk is not a fix. And when you re-roof a historic Grand Rapids home, the skylight gets re-flashed or replaced, never shingled around.
Every skylight starts as a hole someone cut in a good roof. A plain roof plane sheds water because nothing interrupts it. A skylight interrupts it with four edges, and water has to be turned at every one: the uphill head, where snow and runoff pile against the frame, the two sloped sides, and the downhill sill. That is four transitions where the roof meets a vertical curb, and building science treats each the same way it treats a chimney or a dormer, as its own flashing system that has to be right. Get one edge wrong and the roof leaks there first, usually into a ceiling directly below where a stain is impossible to hide.
Grand Rapids stacks the odds the way it always does. The National Weather Service Grand Rapids office tracks 40 to 60 freeze-thaw days in a normal winter, and a skylight's uphill edge is a natural catch point for snow. Meltwater backs up against the curb, refreezes overnight, and works at the seam every day for weeks. A skylight flashed for a mild climate finds that out by February. On a Heritage Hill or Fulton Street corridor home, the leak often surfaces in plaster that is expensive to put back, which is exactly why the flashing is where the money should go.
The single biggest durability decision is the mount. There are two ways a skylight sits on a roof, and in a snow climate they are not equal.
Curb-mounted units sit on a raised wooden curb, typically a few inches tall, built up from the roof deck. The skylight drops onto the curb, and the curb is wrapped in overlapping metal step flashing, the same layered system that waterproofs a chimney base. This is the industry standard for leak resistance. The height lifts the glass above standing water and snowmelt, and the separate flashing means the unit can later be swapped without tearing the flashing apart. On a West Michigan roof that raised, step-flashed curb is the detail that keeps winter out.
Deck-mounted units sit lower and closer to the roof plane, sealed with a factory gasket and a manufacturer flashing kit. They look sleeker and sit more flush, which some homeowners prefer. But they lean harder on that gasket, and with gravity pulling meltwater down and against a lower profile, a deck-mount installed with anything less than a perfect flashing kit is more exposed. An industry breakdown of why deck-mounted skylights leak more readily than curb-mounted lays out the mechanics. Both can perform when installed right. On a historic Grand Rapids roof under lake-effect snow, we lean to the curb.
| Factor | Curb-mounted | Deck-mounted |
|---|---|---|
| Water resistance | Raised curb, overlapping step flashing | Lower profile, gasket plus flashing kit |
| Typical lifespan | About 15 to 40 years | About 15 to 30 years |
| Snow and ice exposure | Glass lifted above the snowline | Sits closer to standing meltwater |
| Future replacement | Swap unit without redoing flashing | Usually disturbs the flashing |
The glass almost never fails. The metal around it does. A correct skylight installation flashes the opening the same disciplined way a dormer sidewall gets flashed. Step flashing climbs the two sloped sides, one L-shaped piece lapped with each shingle course, so the curb and the roof are married step by step. An apron, or sill, flashing turns the downhill edge out onto the shingles. And the uphill head gets a saddle or head flashing, sometimes a small cricket, to split the water and snow around the frame instead of letting it pile against the glass. The pieces are the same family of metal we detail for wall-to-roof joints in our guide to dormer roofing and leak prevention.
What ties it together is order. Flashing works by lapping each piece over the one below so water is always handed downhill onto a surface, never into a seam. Reverse a lap, skip the head saddle, or substitute a bead of sealant for a piece of metal, and the system stops working. This is the identical discipline that governs the most overlooked leak on any old roof, the chimney, which we walk through in chimney flashing on Grand Rapids Heritage Hill roofs. A skylight is a chimney made of glass. Same rules.
The most common skylight repair we are called to undo is a tube of caulk. When a skylight starts dripping, the fast move is to run sealant around the frame where it meets the shingles. It looks like a repair, and it holds for a season. Then the caulk cracks, because sealant sitting in a joint that expands and contracts through a Michigan year cannot carry that load, and the leak comes right back, often worse because water has been tracking behind the failed bead into the sheathing. Caulk has a place as a secondary seal on top of correct metal. It is not a substitute for the flashing kit, and a skylight leak that has only ever been caulked is a skylight that has never really been fixed.
The metal is half the job. The membrane under it is the insurance. Before the step and head flashing goes on, the roof around the curb gets a run of self-adhering ice and water membrane, lapped up the curb behind the metal. Under the International Residential Code that Michigan has adopted, self-adhering underlayment is required at valleys and vulnerable transitions, and section R905.1.2 calls for it where ice-dam risk runs highest. Around a skylight that means if water ever slips past the metal, it lands on a waterproof layer instead of bare wood. We treat that backup as mandatory, the same standard we lay out in ice and water shield requirements under Michigan code.
In a lake-effect winter that hidden layer earns its keep. When snow piles at the uphill edge and an ice dam forms, the membrane is what keeps the meltwater out of the deck and the plaster below. A beautiful new skylight set over a bare deck is a leak on a delay.
Here is where the shortcuts hide. Because skylight flashing is woven into the shingle courses, the only correct way to re-roof a home with a skylight is to strip the old flashing and set a new kit, not shingle up to tired metal. Shingling around an existing skylight to save a day is one of the most common reasons a freshly replaced roof starts staining a ceiling within a year. And there is a timing call worth making honestly: if the skylight is already 20-plus years old, replacing the unit while the roof is open is far cheaper than cutting back into a new roof a few winters later. We raise that before the tear-off, not after.
On a historic Grand Rapids home there is one more layer. In a local historic district such as Heritage Hill, a new or relocated skylight visible from the street can trigger Historic Preservation Commission review, the same process we cover in our Heritage Hill HPC review walkthrough. A skylight tucked on a rear slope is usually straightforward. One on a street-facing elevation is a design conversation before it is a roofing one. We check the district rules before we cut, so the roof ends up both dry and compliant.
A skylight is one of the best things you can do for a dark historic room and one of the easiest openings to build wrong. The glass is rarely the problem. The flashing is: a raised curb wherever the roof allows it, step flashing up the sides, an apron across the sill, a head saddle to split the snow, and a full ice and water membrane underneath, with not a drop of reliance on caulk. Re-roof an old Grand Rapids home and the skylight gets re-flashed or replaced, never shingled around. Do it in that order and the opening you cut for light stays exactly that, and nothing else gets in.
Whether your skylight needs re-flashing, replacement, or a full historic roof around it, our services cover it, and we have been keeping West Michigan roofs dry at their trickiest openings since 1994.
A skylight is an opening cut into the roof, and the only thing keeping water out is the flashing woven around its frame. On an older home that flashing is often original, rusted, or was sealed with caulk instead of layered metal. Add West Michigan snow that piles above the uphill edge and melts into the seam, and the skylight becomes the roof's first leak long before the shingles wear out.
Curb-mounted skylights are the more leak-resistant choice. They sit on a raised wooden curb wrapped in overlapping step flashing, the same layered metal system that waterproofs a chimney, and they lift the glass above snow and standing water. Deck-mounted units sit lower and lean more on a gasket and a factory flashing kit. Both can perform if installed correctly, but the raised curb gives water fewer ways in on a snowy roof.
A quality curb-mounted skylight commonly lasts 15 to 40 years, and a deck-mounted unit around 15 to 30, but the flashing and the seal decide the real number. In a lake-effect climate that cycles through 40 to 60 freeze-thaw days a winter, a unit flashed for looks fails far sooner, while one set on a proper curb over an ice and water membrane runs to the top of its range.
Caulk is not a lasting skylight repair. Sealant run into the joint stops the drip for a season, then cracks as the metal and glass expand and contract through a Michigan year, and the leak returns. A real fix uses a proper flashing kit, step flashing up the sides and an apron across the front, all set over membrane. Caulk belongs on top of correct metal, never in place of it.
Yes. Skylight flashing is woven into the shingle courses, so a correct re-roof strips it and sets a new flashing kit rather than shingling up to tired metal. If the skylight itself is near the end of its life, replacing the unit while the roof is open costs far less than tearing back into a new roof later. Reusing old flashing on a new roof is a shortcut that leaks.
It can. In a local historic district like Heritage Hill, changes visible from the street can fall under Historic Preservation Commission review, and a new skylight on a street-facing slope is the kind of change that may need a certificate of appropriateness. A skylight on a rear or hidden slope is usually far simpler. We check the district rules before we cut, so the roof stays both dry and compliant.
Roof Repair of Grand Rapids has been installing, repairing, and preserving roof systems on West Michigan homes since 1994. Our crews flash skylights the same exacting way we flash dormers and chimneys, setting curb-mounted units on step-flashed curbs, splitting the snow at the head, and laying full ice and water membrane before a single piece of metal goes down. On historic homes we check the district rules before we cut and re-flash every opening on a re-roof rather than shingling around it, because on a Grand Rapids roof the skylight is where winter goes looking for a way in. Reference for this guide: an industry analysis of curb-mounted versus deck-mounted skylight leak risk.