Skylights and Clerestory Glass on Costa Mesa, CA Mid-Century Homes: Beautiful, and a Leak Risk
The skylights and clerestory windows that give Costa Mesa's mid-century homes their light are also some of the most common places a roof leaks. Here is why, and what to do about it.
Light was a design priority, and it left openings
One of the things that makes Costa Mesa's mid-century homes so appealing is how much natural light they bring in. The architects of that era loved daylight, and they got it into these low-slung homes with features that punch openings right through the roof, skylights set into the roof plane and clerestory windows, the bands of glass set high on a wall just below the roofline that let light pour in over the top of the rooms. Those features are a big part of the homes' character and a big part of why people love them, and they are also, from a roofing standpoint, a series of holes deliberately cut into the roof and into the junction between roof and wall.
Every one of those openings is a place where the roof's waterproofing had to be interrupted and then carefully sealed back up, and anything that has to be sealed can eventually leak. A solid roof plane is the easy part. The hard part is everywhere the roof has to wrap around or seal against something else, and skylights and clerestories create a lot of that hard part. So the very features that give these Costa Mesa homes their light also give them more than the usual number of places for water to find a way in, which is why these homes turn up so often when a leak needs tracing.
Why skylights leak, and what fails
A skylight is a large opening cut into the roof, and sealing a large opening is harder than sealing a small one, simply because there is more perimeter to seal and more flashing to fail. The flashing around a skylight, the curb flashing that wraps the raised frame and ties it into the surrounding roof, is what keeps water out, and it is the part that gives trouble. Over the years the daily temperature swing works the flashing and the sealant, the marine-layer damp keeps it from drying, and eventually a section loosens or a bead of sealant cracks, and water that hits the roof above the skylight runs down and finds the gap. The glass itself is rarely the problem. It is almost always the flashing around the opening.
Older skylights are a particular concern on these mid-century homes. Many are decades old, some are the original units, and skylight technology and the sealants used around them have improved a great deal over the years, so an old skylight is both more likely to have failing flashing and more likely to be a poorly sealed design to begin with. A leak that shows up near a skylight is also tricky to read, because water that enters at the skylight curb runs along the framing before it drips, so the stain can appear some distance away, which sends homeowners and careless roofers looking in the wrong place. When there is a leak anywhere near a skylight, the skylight is the first thing we check, because the odds are very good the opening, not the glass, is where the water is getting in.
- Skylights and clerestories are openings cut into the roof and roofline
- The flashing around the opening fails, not usually the glass
- Daily temperature swing and marine damp wear the flashing and sealant
- Older original skylights are both more worn and more poorly sealed
- Water enters at the opening but the stain can appear far away
Clerestories and the roof-to-wall junction
Clerestory windows add a different version of the same problem. A clerestory is a band of glass set high on a wall, just below where the roof meets that wall, and it puts a window right at one of the trickiest junctions on any roof, the spot where the roof plane terminates against a vertical wall. That roof-to-wall junction is already a place that demands careful flashing to keep water out, and adding a run of windows just below it complicates the detailing further, because now the flashing has to manage water coming off the roof, direct it away from the wall, and do so right above a line of glass that will show any failure as a leak indoors.
When these junctions leak, it is usually because the flashing where the roof meets the wall has loosened or was not detailed well to begin with, or because the sealing around the clerestory frames themselves has failed with age. The daily thermal movement and the constant coastal damp work this junction the same way they work a skylight, and a clerestory leak can be especially frustrating to trace because the water can travel within the wall before it appears. These are exactly the kind of leaks that reward a roofer who understands how these mid-century homes are put together and who knows to look at the roof-to-wall flashing and the clerestory sealing rather than guessing at the open roof field, which is almost never the culprit.
Keeping the light without the leaks
None of this is an argument against the skylights and clerestories that make these homes special. It is an argument for maintaining them properly, because with the right attention these features can let in their light for decades without leaking. The maintenance is mostly about the flashing and the sealant at every opening, keeping the curb flashing around the skylights sound, keeping the roof-to-wall flashing below the clerestories intact, and refreshing the sealant at these details before the daily temperature swing and the marine damp wear it out. A skylight or clerestory whose flashing is kept in good order is not a leak risk. One that is ignored for years until the sealant cracks is one of the most reliable leak sources on the whole roof.
When a skylight is genuinely old and failing, replacing the unit at the same time the surrounding roof is worked on is often the smart move, because a modern, well-sealed skylight set into properly detailed new flashing is a far more reliable proposition than nursing a decades-old unit through another round of resealing. The same logic applies when one of these homes is re-roofed, the moment to get every skylight and every clerestory junction detailed correctly is while the roof is open and the crew is already addressing the flashing throughout. Building these details right during a re-roof is what lets the new roof keep the home's light without inheriting its leaks.
If you own one of these light-filled Costa Mesa homes and you have a leak, or you simply want to head off one, the skylights and the clerestory junctions are exactly where a careful inspection should focus, because experience says that is where the water on these homes almost always gets in. We will check the flashing and the sealing at every opening, trace any active leak back to its real source rather than guessing from the stain, and tell you honestly whether you are looking at a simple reseal, a flashing rebuild, or an aging unit worth replacing. Keeping the light is entirely compatible with keeping the water out, as long as the openings that bring the light in are given the attention they need.
The skylights and clerestory windows that make your Costa Mesa home so bright are also where it most often leaks, and the flashing is almost always the cause. If yours are leaking or you want to get ahead of it, we will trace it to the source. Call 949-390-6295.
If that sounds right, call 949-390-6295 and we will take an honest look.