Skylights · Service

Replacing a skylight you already have

The opening exists, so the decisions are different: whether the unit is genuinely finished, whether the new one has to match the curb, and why the age of your roof matters more than the age of the skylight.

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In short

What is skylight replacement?

Replacing a skylight means removing the old unit and its flashing, checking and repairing the deck and curb underneath, setting a new unit sized to the opening you already have, and reflashing it into the surrounding roof covering. The opening usually stays; the flashing always gets replaced. The decision that matters most is not the skylight's age — it is how many years your roof has left, because doing both together costs far less than doing them apart.

Triggers

Signs you need skylight replacement

There is moisture or a permanent haze between the panes of glass, which means the sealed unit has failed and cannot be repaired — only replaced
The frame is an old acrylic or polycarbonate dome that has gone yellow, crazed or brittle, and flexes when you press it
You are getting repeated leaks at the same skylight despite the flashing having been redone, which usually means the curb or the deck edge under it has rotted
A venting unit no longer closes squarely, the seal no longer compresses evenly, or the operator has failed and the parts are no longer made
The roof is being replaced and the skylight is old enough that leaving it means opening the new roof again in a few years
The unit predates modern glazing and the room is uncomfortable — old single-glazed or uncoated units both leak heat in winter and dump it in in summer

Seeing something not on this list? Browse skylights problems by symptom →

The job

How skylight replacement actually works

Diagnose before quoting — is it the unit, or is it the flashing?

A leak at a skylight is more often a flashing or a sealant failure than a unit failure. A competent assessment separates the two: failed glazing seals show as moisture between panes or a permanent film that will not clean off; failed flashing shows as staining at the head or the sides that tracks with rain. Replacing a sound unit because the flashing leaked is a common and expensive misdiagnosis.

Watch for: A quote for a new unit produced without anyone going onto the roof or into the attic. If nobody has looked at the flashing and the deck around the curb, the diagnosis is a guess with a product attached.
Measure the existing opening and decide match-or-change

Replacements are sized to the opening you have. Deck-mounted units are sized to the rough opening in the deck; curb-mounted units are sized to the outside of the existing curb, and a unit that is nominally the same size from a different maker frequently is not. Changing size is possible but converts the job into partial reframing, with headers and interior finishing following.

Watch for: A size taken from the visible interior trim rather than from the actual rough opening or curb. It is the single most common cause of a replacement unit arriving that does not fit, and it costs a return trip and an open roof overnight.
Strip back the covering and remove the old unit

The roof covering is lifted back far enough around the opening to get the old flashing out cleanly — the sides and, in particular, the head, where the flashing runs up under courses that have to be freed rather than cut. The old unit is lifted out and the opening covered if the job runs over a day.

Watch for: Old flashing cut off flush and left in place under the covering. It has to come out. Layered flashing traps water between the old and new detail and produces a leak nobody can find.
Inspect and repair the deck, the curb and the framing

This is the part you cannot see from a quote and the part that generates change orders. Years of a slow leak rot the deck edge at the head of the opening and the base of a wooden curb. Both are repaired before anything new goes on, and on an older curb-mounted unit the curb is often rebuilt.

Watch for: A price with no allowance and no conversation about what happens if there is rot. Ask for a stated hourly or unit rate for deck and curb repair up front, so the discovery is priced rather than negotiated on the day.
Set the new unit and install a complete new flashing kit

The new unit goes in with the flashing kit made for that model and for your roof covering. This kit is always new — flashing is not reused, even where it looks serviceable, because it has been formed to the old unit and it has done its service life.

Watch for: Reused step flashing, or a mismatched kit because "the sizes are close". Manufacturers tie the unit warranty to their own kit correctly installed, so a saved hundred dollars here typically forfeits the warranty on the unit you just bought.
Reinstate the covering and make good inside

The roof covering is laid back over the flashing in the correct order, and inside, the shaft and trim are repaired where the old unit had been leaking. Where there was a long-running leak, the shaft insulation is usually wet and gets replaced rather than dried in place.

Watch for: Wet insulation left in a shaft and simply covered over with new drywall. It will not dry inside a sealed cavity, and the smell and the staining come back within a season.

Money

What does skylight replacement cost?

A like-for-like replacement into a sound existing opening is typically a one-day job plus the unit, and costs well below a new installation because there is no framing or shaft work. Deck or curb rot, size changes and low-slope roofs add to it. See the skylight cost guide for ranges.

See the full skylight replacement cost guide — by material, size and region →

Straight answer

When skylight replacement is the wrong call

Everyone else ranking for this is paid when you say yes. Here's when you shouldn't.

The glass is intact and only the flashing has failed. Reflashing a sound unit is a fraction of the price of replacing it. Get the diagnosis separated before you accept a quote that bundles them, because the bundle is where the margin is.
Your roof is due within a couple of years. Replacing the skylight now means paying for the flashing labour twice and tearing out new work at reroofing. Reseal it to get through, and put the replacement in the roofing contract where the covering is already off.
The unit is under twenty years old, sound, and the roof is coming off anyway. Replacing the flashing kit and reseating the existing unit is usually the right middle option — the flashing and seals have a shorter service life than the unit, and that is what you are actually buying.
What you actually want is a different position or more light. Then this is not a replacement, it is a new installation plus the closing up of an old opening, and it should be scoped and priced as one. Sliding a bigger unit into a slightly enlarged hole is how badly supported openings happen.
The problem is condensation, not water ingress. If it appears in cold weather rather than during rain, the shaft air sealing and the room's humidity are the fault, and a new skylight will condense exactly as the old one did.
You cannot find out what the existing unit is. On an unlabelled older curb-mounted unit, the sensible order is to open it up and measure the curb before ordering anything. Committing to a product before the curb has been seen is how a job stalls with the roof open.

Your options

Types of skylight replacement

Like-for-like unit

Same size, same mounting, minimum disruption — the default when the opening and curb are sound.

Upgrade the glazing

The moment to move to laminated or low-emissivity glass, since the labour is already committed.

Convert to a venting unit

Possible within the same opening, and where a manual unit becomes solar-powered it needs no wiring.

Close it up instead

If the skylight was a mistake, replacing it with roof deck and insulation is a legitimate outcome. Discuss it with the roofer.

Compare skylights options side by side →

Before you sign

What to check when hiring for skylight replacement

Have you been on the roof and into the attic before pricing this?

A replacement quote that has not looked at the flashing, the deck at the head of the opening, and the shaft from underneath is not a diagnosis. All three change the price.
Is the glazing failed, or is this a flashing job?

They are different repairs at very different prices. You want the reasoning, not a conclusion — moisture between panes points one way, staining that tracks with rainfall points the other.
What size is the existing opening or curb, and how did you measure it?

Measured from the rough opening or the outside of the curb, not from the interior trim. This is what stops the wrong unit turning up.
What is your rate if you find rot in the deck or the curb?

The most likely extra on this job. Agreeing a rate before the roof is open is a very different conversation from agreeing one after.
Is a complete new manufacturer flashing kit included?

It should be, and it should be itemised. Reused or generic flashing is both the leak risk and the thing that voids the new unit's warranty.
Who repairs the interior — the shaft, the drywall, the paint?

Where there has been a leak there is interior damage, and plenty of roofing contractors exclude interior finishing entirely. Establish the boundary in writing.
How is the roof protected if the job runs past one day?

Replacements find surprises. You want to hear a specific plan for a watertight temporary cover, not an assurance that it will be finished.

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Local pros

Skylight Replacement near you

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Related work

Often done at the same time

Skylight Installation

A new opening rather than an existing one

Skylight Repair

When the unit itself is still sound

Solar Powered Skylight

Upgrading a fixed unit to a venting one

Tubular Skylight Installation

Adding daylight elsewhere in the house

All skylights services →

FAQ

Skylight Replacement — questions people ask

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How do I know whether to replace or just reseal my skylight?

Moisture or permanent haze between the panes means the sealed glazing unit has failed, and that is a replacement — it cannot be repaired in place. Staining at the head or sides that appears with rain and dries afterwards points at the flashing, which can usually be redone with the unit staying put. If the frame flexes, an acrylic dome has crazed, or a venting mechanism has failed with no parts available, replacement is the practical answer.

Can I put a different brand of skylight into my existing opening?

Often, but do not assume the sizes interchange. Curb-mounted units are sized to the outside of the curb and nominally identical sizes between manufacturers frequently differ by enough to matter, while deck-mounted units are sized to the rough opening in the deck. Have the actual opening measured before anything is ordered, and be ready for minor curb modification as part of the job.

Should I replace my skylights when I replace the roof?

If they are old, yes — the access, staging and covering work are shared, so the marginal cost is much lower than doing it separately, and a skylight left in place will eventually mean opening a new roof. If they are relatively young and sound, replacing the flashing kit and reseating them is the sensible middle path, because the flashing has a shorter life than the unit and it is the flashing that leaks.

How long does a skylight replacement take?

A like-for-like swap into a sound opening is commonly a single day per unit. It extends when the deck or curb has rotted, when the covering is tile or metal and has to be carefully lifted and reinstated, when the size changes, or when interior repair is needed after a long-running leak — drywall and paint add days that are mostly drying time.

Is it worth replacing an old skylight for energy reasons alone?

On its own, rarely the strongest case. An old single-glazed or uncoated unit is genuinely a weak point in the ceiling plane and a modern one is much better, but the comfort improvement — less winter draught and radiant chill, less summer heat gain — is usually the honest reason rather than a calculable payback. Treat improved comfort as the benefit and any energy saving as a bonus.

Does replacing a skylight need a permit?

It varies, and it often turns on whether the opening changes. Many jurisdictions treat a like-for-like replacement into an existing opening more lightly than a new opening, while any change in size brings the structural framing back into scope. Some also apply energy requirements to the replacement glazing. Check with your building department and make the responsibility explicit in the contract.