Replacing a skylight you already have

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.

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 →

How skylight replacement actually works

1. 1

   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 forA 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.

2. 2

   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 forA 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.

3. 3

   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 forOld 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.

4. 4

   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 forA 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.

5. 5

   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 forReused 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.

6. 6

   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 forWet 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.

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 →

If the number is the problem, here are the ways people pay for it →