Heat gets through skylights and melts the snow on them, then the water goes downhill onto the cold roof below, and an ice dam is created. Water can dam high enough to come in through the skylight’s rim weatherstripping, typically at the latch point.
What are you doing to get as problem-free as possible?
BTW, I traveled to Sweden once in winter, visiting the big university town of Uppsala about an hour north of Stockholm. Up on those snow-covered roofs everywhere, were skylights of all shapes and sizes. I believe Velux is a Swedish company.
I have only used Velux skylights, with their flash surrounds. I have used them on single and stacked skylights, in snow country, and have had no leaks. But, to qualify that, in times of heavy snow, I use a snow rake to clear the areas just below lites.
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Remove shingles below the skylight and install eave protection like "Ice and Water shield" the same way you'd do at the eaves, take it up to beyond the leak points, then re-do shingles.
Another solution would be electric heating cables to be turned on when the weather and snow loads are conducive to leakage occurring.
Gift wrap the skylights with ice and water shield. A foot or more on the bottom, two to three feet above the top. Six inches at least from the sides, nailing the flashing to the skylight and not the roof. Velux is an excellent product and so long as you meet or excede specs you should be good in most instances(short of a shallow sloped roof). An operating light creates new problems. Room heat exits the light and warms any piled snow which in turn runs down away from the warmth until it refreezes. If the slope of the roof is too shallow the ice dam builds up quickly, working it's way into any operating seals. Short of resloping the roof (yeah right) a warming system that keeps the snow below (as in downslope) the skylight from refreezing and flowing into the gutter is called for. Warming wires may need to be run in the gutter itself and possibly down the downspout to insure liquid water drainage. You want any water to remain liquid so that you can direct it away from the home's openings. Once it freezes up it willl back up and work its way into the warm space of your home.
It sounds like the problem is that the dam is overtopping the curb of the operable skylight, so simply sealing the flashing better isn't going to do any good. You either need to keep the skylight colder, or cause the ice to drain away below.
Under the circumstances, probably the simplest solution is a heater cable downhill from the skylight. These need to be turned on/off somewhat manually, and need to be replaced about every three years (when they begin to crack), so they're not maintenance-free.
Otherwise, you could add a interior "storm" to keep the skylight cooler, but you'd have trouble with condensation then.
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I always wrap the wppd frame with ice and water shield before using the flashing. I ama Velux fan too. happened to see them every wheere recently on my trip to Ireland.
With the problem you describe, you must have a combination of two things - a fairly low slope condition which would call for total ice and water shield anyway, and a vcary cold winter tempe4rature. If yto are still haveing trouble with adding the I&W, you will probably have to add a heat cable to provide a clear draine path.
On new installs, I also foam the devil out of the unit before truimmiong it to reduice the cold spots t the skylight
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Velux sells a deck mount fixed skylight, which I have used, and also a curb-mount fixed skylight, with which I've no experience.
The curb-mount might be best in snow country because the curb, which you build and flash before installing the framed IG-lensed lite atop, can be built higher than what is achieved when using the deckmount model.
Have you used the curb-mount model? A pic is attached I clipped from the Velux site.
View Image
I haven't, and agree that in theory that would be better in snbow country, but what you have pictured looks just like the normal ones we use. Sure you got the right picture?
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Yes. Their instructions describe using 2x material at the perimeter to build the curb, and says it should be a minimum of 3-1/2" high. I guess you can go higher, but too much and you might as well be doing crickets above.
I installed 2 like the one you have pictured.( this past july)
Definitely get the factory pre-fab flashing kit.
You can build the curb out of 2x6------in fact if you use 2x4 you will have to trim down the supplied step flashing. I wrap the the surrounding deck and up the curb with ice gaurd----about 30-36 " all around----making sure the bottom icegaurd spills any water back out onto the shingles------and not under the shingles. If you can---use the smooth faced icegaurd----as it sticks to itself better than the granulated and you can wrap the curb tighter.
Best wishes,
Stephen