Doing skylights and shingles at the same time saves money and prevents leaks. Doing them out of order is one of the most common ways a Calgary re-roof ends up leaking anyway.
If your home has skylights and the roof is due for replacement, the timing question matters more than most homeowners realize. Replacing skylights and shingles together, in the right sequence, is cheaper and more reliable than doing either one alone. Getting the order wrong, or skipping one while doing the other, is one of the more common reasons a freshly reroofed Calgary home develops a leak within the first year or two.
This guide explains why sequencing matters, what a proper skylight-and-reroof job actually involves, and the cost and leak risks of treating them as two separate, unrelated projects.
Why skylights are a common leak point in the first place
A skylight is a hole cut deliberately into the roof, and every seam around its frame is a place water can find a way in if the flashing is not done correctly. Skylight flashing kits are specific to the skylight model and roof pitch, and proper installation involves step flashing integrated with the surrounding shingle courses, not just caulk applied around the edges.
Skylights installed a decade or more ago often used flashing systems that have since been superseded by better designs, and the rubber gaskets and seals inside older units degrade with UV and temperature cycling over time, independent of whether the surrounding shingles are new or old. A skylight that has never leaked can still be nearing the point where its seals are the weak link on an otherwise sound roof.
Why doing both at once is the efficient choice
When shingles and skylight flashing are replaced in the same project, the crew integrates the new flashing with the new shingle courses in one continuous, correctly layered installation. This is both faster and more reliable than adding new flashing around an old skylight after the fact, or shingling around an existing skylight frame that was never designed to interface with new roofing materials.
There is a real cost efficiency too. Mobilizing a crew, scaffolding or ladder access, and disposal logistics are shared costs across the whole project. Doing skylight work as a completely separate job later means paying those setup costs twice instead of once.
What happens when the sequencing goes wrong
The most common mistake is shingling a full reroof around an existing older skylight without addressing its flashing or condition, on the assumption that the skylight is “fine” because it is not currently leaking. A skylight with degrading seals or outdated flashing that gets shingled around, rather than properly integrated, can begin leaking within a year or two, and now the fix requires disturbing brand-new shingles to get at the flashing underneath.
The reverse mistake also happens: replacing an old, worn skylight on its own, in isolation from a roof that is also nearing end of life, means paying for skylight flashing work now and paying to redo essentially the same flashing again in a few years when the surrounding shingles finally get replaced too.
Questions to ask before your reroof begins
If your home has existing skylights and you are planning a reroof, raise the question directly rather than assuming the contractor will flag it. Ask them to inspect the skylight’s current flashing, seals, and general condition as part of the pre-project assessment, not as an afterthought discovered mid-project.
Get a clear answer on whether the existing skylights will be re-flashed as part of the reroof at no additional integration cost, or whether skylight replacement is recommended based on their age and condition, with a separate price for that work.
- Ask for a skylight condition assessment as part of the roof inspection.
- Confirm whether flashing will be integrated with new shingle courses.
- Get a separate, itemized price if skylight replacement is recommended.
- Ask how old the current skylights are and their typical seal lifespan.
- Request the flashing kit be matched to the exact skylight model and pitch.
- Confirm any skylight warranty terms alongside the shingle warranty.
When skipping skylight work is genuinely fine
Not every reroof needs skylight replacement. A newer skylight with intact seals and modern flashing can often simply be re-integrated with fresh flashing during the reroof without needing full unit replacement, which is a much smaller cost. The point is not that skylights always need replacing alongside a reroof; it is that the decision should be made deliberately, based on an actual inspection, rather than by default because nobody raised the question.
Skylight leaks that have nothing to do with the roof
Not every leak near a skylight is a flashing failure. Condensation forming on the inside of the glazing during cold Calgary mornings can drip and look identical to a genuine leak, especially on older single-pane or poorly sealed units. Interior humidity from cooking, showers, or houseplants rising into a cold attic space above a skylight shaft can also condense and mimic a roof leak entirely unrelated to the flashing outside.
Before assuming a skylight leak means the flashing needs redoing, rule out condensation by checking whether the moisture appears specifically during cold snaps or after humid activity indoors, versus during or immediately after rain or snowmelt. A genuine flashing leak tracks with weather events outside; condensation tracks with temperature and humidity swings inside, and confusing the two leads to spending money on flashing work that will not fix the actual problem.
Upgrading the skylight itself during a reroof
A reroof is the natural moment to consider upgrading an older skylight rather than simply reinstalling the same unit with new flashing. Modern skylights offer meaningfully better sealing, glazing, and in some cases remote-operated venting or built-in shades that older units did not have, and the labour to access and integrate the flashing is already being spent regardless of whether the unit itself is upgraded.
This is not a requirement, and plenty of well-maintained existing skylights are worth keeping as-is through a reroof. It is simply worth a direct conversation: ask your contractor whether your specific skylight model is old enough, typically anywhere past 15 to 20 years, that upgrading makes more sense than reflashing the original unit again.
What bundled skylight work typically adds to a reroof
Reflashing an existing, structurally sound skylight as part of a reroof adds a modest cost per unit compared to doing the shingles alone, reflecting the flashing kit and the additional labour to integrate it properly with the new shingle courses. Full skylight replacement, unit and flashing together, costs meaningfully more per skylight but still benefits from the shared mobilization cost of the larger reroof project already underway.
Either way, bundling skylight work into the reroof is close to always cheaper than addressing it as a fully separate project later, simply because the crew, equipment, and access are already in place. Ask for the skylight work to be broken out as its own line item on your quote so you can see exactly what it adds to the total.
Skylight shafts and insulation: a related consideration
The shaft connecting a skylight to the ceiling below runs through the attic space, and if it is poorly insulated or sealed where it passes through, it becomes both a heat loss point and a spot where condensation can form, sometimes mistaken for a roof or flashing leak. A reroof does not automatically address shaft insulation, since that work happens inside the attic rather than on the roof surface.
While your contractor is up assessing the skylight from outside, it costs little extra to check the shaft’s insulation and air sealing from the attic side at the same time, particularly if condensation-related staining has ever appeared around the skylight indoors.
A note for flat or low-slope skylights
Flat-mounted skylights and light tubes on low-slope roof sections face different water-shedding challenges than a pitched skylight, and their flashing details differ accordingly. If your home has this style, confirm your contractor has specific experience with low-slope skylight flashing rather than assuming the same approach used on a steep roof applies equally well here.
Ask before the shingles go down, not after
Skylights and shingles share the same roof plane, and treating them as unrelated projects is how avoidable leaks happen. The fix is simple: raise the question before your reroof starts, get an honest assessment of your existing skylights, and let the flashing decision be made on purpose.
If a reroof is coming up on a home with existing skylights, ask your contractor about sequencing roof installation around skylights in Calgary before the crew arrives. It is a five-minute conversation that can save you a mid-winter leak two years down the road.
About the author: this article was contributed by Angel’s Roofing, a Calgary roofing contractor certified in VELUX skylight installation and flashing integration. The company assesses existing skylight condition as a standard part of every residential reroof quote.