What changes when a skylight goes in during a roof replacement - the flashing kit, the sequencing, and why fitting one at any other time is the expensive option.
Reviewed by Michael ThompsonThis page covers skylight installation as part of a roofing project. For the full guide - every option, the complete process and detailed pricing - see our main skylight installation guide.
Fitting a skylight means cutting an opening through the roof deck, framing it, setting the unit, and - the part that decides whether it ever leaks - installing the manufacturer's step-flashing kit woven into the surrounding courses of roof covering. That last step is why a roof replacement is overwhelmingly the right moment: the covering is already off, the flashing can be integrated properly rather than retro-fitted around existing material, and one crew owns the whole detail.
Position it from inside, not from the roof
Where the light lands in the room depends on the rafter bay available, the shaft angle through the attic, and the roof orientation. The position is settled from below, then transferred up.
Watch forA location chosen purely for the roofer's convenience between rafters. It is the one decision you live with permanently, and moving a skylight after the fact means patching a roof.
Opening and framing
The deck is cut and the opening framed with headers so the cut rafters are supported. Where the ceiling is below an attic, a light shaft is built and insulated between the roof opening and the ceiling opening.
Watch forRafters cut without headers. This is structural work, not carpentry-by-eye, and an unheadered opening transfers load into the surrounding rafters that they were not sized for.
Setting the unit and installing the flashing kit
The skylight is set on the deck or on a built curb, then flashed with the manufacturer's kit for that model and that roof covering - a head flashing, sill, and step pieces that interleave with each shingle course as the roof is laid up around it.
Watch forA generic flashing detail or a bed of sealant instead of the model-specific kit. Skylights have a reputation for leaking that is very largely a reputation for being badly flashed, and using the wrong kit usually voids the manufacturer warranty as well.
Sealing and finishing the interior
The shaft is insulated and air-sealed to the same standard as the rest of the ceiling plane, then finished. Poor air sealing here condenses moisture around the opening in winter, which then gets reported as a leak.
Watch forCondensation around the frame blamed on the unit. If it appears in cold weather and not in rain, the problem is warm humid air reaching a cold surface - an insulation and sealing issue, not a roofing one.
Adding a skylight during a roof replacement is far cheaper than as a standalone job, because access, staging and the surrounding roof work are already in hand. Unit price varies widely by size, glazing and whether it opens. See the skylight cost guide for ranges.
See the full skylight installation cost guide - by material, size and region →
HomeMatchup is not a roofing contractor. We don't sell equipment, we don't quote jobs and we never show up at your house. What we do is one thing: put your job in front of the local pros who are licensed, insured and actually take work like yours - so you're choosing between vetted options instead of gambling on whoever answers the phone first.
Your ZIP and a short description. About 60 seconds, and no, you don't need to know what the work should cost - that's the part we're helping with.
We route it to pros who work your area and hold the licence the job legally requires. You stop being the person calling six numbers and leaving five voicemails.
Quotes come to you. Compare them against the checklist further down this page, then hire whoever you want - or nobody. There's no fee and no obligation either way.
Free to you · No obligation to hire · Only your matched pros get your details · How we vet pros
Everyone else ranking for this is paid when you say yes. Here's when you shouldn't.
Local pro matching for skylight installation is rolling out by metro. Enter your ZIP and we'll match you with vetted pros in your area today.
Tell us what you need and we'll match you with vetted local roofing pros - free.
Free · No pressure · Licensed & insured pros
Twenty years on and around home improvement work. Reads our guides for the things that are technically true and practically wrong.
Every guide on this site is written by a member of our team and checked by someone else before it publishes, and every figure carries the source and the date we pulled it. Found a number that looks off? Tell us - corrections are the cheapest quality control we have.