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Question DetailsAsked on 11/14/2017

are skylights eventually problems?

roofing on my home

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They certainly have a reputation for that - partly because when they leak it usually is into the house directly or staining the ceiling rather than onto the insulation in the attic, which conceals minor leaks in many houses. Properly flashed and sealed they can last decades without leaking - especially if the glazing unit (the glass or plastic) has metal over-flashing on the seal so the seal around the glazing unit is not directly esposed to weather.


Sometimes the "leak" is not a leak at all, but condensation on the inside from the warm moist household air hitting the interior of the frame or glass and condensing, causing interior drips - that is probably over 2/3 of the issues with skylights that I have seen.


The acrylic "dome" types do tend to crack or haze or leak in about 15-20 years or so, and in heavy snow areas I have seen them invert under the snow load and become a pond on topo andleak, so I do not see those as a "lifetime of the roof" product.


Also, in areas with heavy snow, which causes icing and water backup around the warmer skylight, leaks around the flashing at the roofline are more common - as is damage from being hit with snow shovel or snow rake if the roof is cleared of snow during the winter. I have also seen some leaking ones from corrosion caused by people throwing ice melt onto the roof to keep it thawed out around the skylights - neither steel nor aluminum housings like ice melt, which is usually a salt of one type or another.


The main problem I see is many (maybe most) manufacturers and installers either do not understand the principles of flashing and waterproofing for roof penetrations or do not go to the trouble of detailing out the exact measures needed to provide a good water seal and to prevent underflow. it is similar to keeping water out of window openings in walls, but tougher because the water is constantly (when raining or melting) running down around the skylight, and sometimes backing up around it on the uphill side and on flatter roofs, so there is a lot more opportunity for significant leakage unless the job is done totally right. This lack of detailing of the water barrier is commonly aggravated by installing it in the wrong order in the roofing layers, cutting through (so providing a water path through the water barrier layers) or omitting or not properly lapping and seaming ice and water shield or roof wrap in that area, or plain inexperience - in most areas window guys and roofers do not do a whole lot of them, so they do not see as many of the causes of failures which it would take to teach them the right and wrong way to do it.


Another aggravating factor is they commonly are installed flush on the sheathing, rather than being raised on firring strips or a base platform so the water barriers drain roof runoff water away from and around them instead of letting it run right down to and around it in direct contact.


And of course expensive to fix or replace, so for low-slope roofs (flatter than say 3:12 slope or no raised platform in the roofing around them on flat roofs) or parts of roofs which may possibly see water backup or icing, I recommend against them. Except in heavy snow country or serious icing country, or hurricane country where impact damage to the skylight can break it, generally locations higher up on the roof (though you have to watch inside temperature and air circulation to avoid condensation issues in areas with winters) can work OK.


Another alternative, which uses materials and methods more like exhaust duct roof penetrations do, is light tubes - small round tubes with a glasson top, like a nmin-skyulight - but they tend to avoid many of the full-sized skylight issues because of the small penetration. But of course, while fine for attics and bathrooms and such, they do not let in a large amount of light - and of course, the more roof penetrations, the more potential leakage spots.

Answered 8 days ago by LCD




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