Skylight installation cost

Installing a skylight into an existing roof costs $1,000 to $3,500, typically around $1,800. Replacing one already there is cheaper at $800 to $2,400, because the hole and the framing already exist.

Almost everything people believe about skylights comes from the ones installed in the 1980s, which leaked. Modern units with a proper flashing kit do not, and the ones that still do are almost always a flashing failure rather than a glass one.

What it costs

The unit itself is $300 to $1,500 of that. The rest is labor, flashing, roofing work around the opening, and the interior finish.

Fixed, venting, or a tube

Fixed does not open. Cheapest, fewest things to fail, and the right answer wherever the room does not need ventilation.

Venting opens, either by a crank pole or a motor. Worth the money in a bathroom or a kitchen where it removes moisture, and in a stairwell where it vents heat off the top of the house in summer. Motorized units with rain sensors close themselves, which is the feature people who have owned a manual one always want.

Tubular, sold as sun tunnels, are a 10 to 14 inch reflective tube from a small roof dome to a ceiling diffuser. $500 to $1,500, no framing changes, and they bring a surprising amount of daylight into an interior hallway or a windowless bathroom. They do not give a view of the sky, which for some people is the entire point of a skylight.

Where it goes matters more than which one

Rafter spacing. A skylight that fits between two rafters needs no structural work. One wider than the bay means cutting a rafter and adding headers, which is $500 to $1,500 and, on a load-bearing roof, sometimes an engineer.

Which slope. North-facing gives steady, even light all day and almost no heat. South-facing gives dramatic light and a significant summer heat load — worth it with a low-emissivity glass and a blind, punishing without. East gives morning light, west gives late afternoon glare and heat.

Distance to the ridge and the eave. Flashing kits need a minimum run of roof above and below to shed water properly. Too close to a valley is the worst place of all, because that is where the roof concentrates its water.

The flashing kit is the whole job

Buy the manufacturer's flashing kit made for your roof covering and your skylight model. Not a generic one, not a bed of sealant.

Skylights that leak leak at the flashing, and the flashing fails for three reasons: the wrong kit, a kit fitted out of sequence with the shingles, or sealant used as the waterproofing instead of as a secondary measure. All three are installation choices, not product defects.

Ask which kit is being used and whether it is the one made for your roof material. The answer takes ten seconds and predicts the next twenty years.

Glass, and the numbers on the label

Laminated glass rather than tempered on anything above a living space: laminated holds together if it breaks, tempered falls as pellets. Many codes require it overhead.

Low-emissivity coating with argon fill is standard on decent units and cuts heat gain and loss substantially.

Solar heat gain coefficient. Lower is better in the south, and on a south-facing installation it matters more than the U-value.

Blinds, cellular or blackout, are $150 to $600 and are the difference between a bedroom skylight that is pleasant and one that wakes you at five in the morning.

Frequently asked questions

Do skylights leak?

Properly flashed modern units, no. Nearly every leak traced to a skylight is the flashing, condensation misread as a leak, or a unit past its 20 to 30 year service life. The glazing seal fails eventually like any double-glazed unit.

How long do they last?

Twenty to thirty years for the unit. The flashing lasts as long as the roof around it, which is why the sensible time to replace a skylight is when the roof is replaced.

Should I replace them when I replace the roof?

If they are more than fifteen years old, yes. The labor is largely shared, and leaving a twenty-year-old skylight in a new roof means opening that roof again in five years.

Will it make the room too hot?

On a south or west slope without low-e glass, yes, noticeably. With modern glazing and a blind it is manageable. A venting unit turns the heat into an advantage by letting it out.

Can one be added to a flat roof?

Yes, on a curb that raises it above the membrane. It costs more than a pitched installation because the curb has to be built and flashed into the membrane, and it must be tall enough that standing water cannot reach the glass.