Skylights · Guides

Skylight guides

A good skylight project is decided before anyone touches the roof: where the light lands, how big the unit is, whether the ceiling is flat or cathedral, and whether the framing allows an opening there at all. Orientation drives comfort — north-facing gives even light, south and west bring heat, which is why ENERGY STAR skylight criteria are set on NFRC U-factor and SHGC ratings that differ by climate zone. Get the placement and glazing right and the rest is execution.

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Start in the attic, not on the roof. Whether a skylight can go where you want depends on rafter or truss spacing, ducts, wiring and plumbing vents above the ceiling. Truss roofs in particular can't have members cut without an engineer's involvement — a contractor who shrugs that off is not the one to hire.

Then decide the ceiling. A cathedral ceiling means the skylight is essentially flush with the room and the job is simpler. A flat ceiling with attic above means building a light shaft, which is drywall, insulation, corner bead and paint — real cost, and the part most often left out of a cheap quote. A splayed shaft spreads light better than a straight one.

Fixed, venting or tubular is a use question. Fixed is for light only and is the cheapest and most reliable. Venting adds ventilation — genuinely useful in bathrooms and kitchens — at roughly double the material cost in Fixr's figures, plus possible electrical work at around $435–$793. Tubular is for small dark spaces like hallways, closets and interior bathrooms where a full shaft isn't practical.

Finally, sequence it with the roof. VELUX's guidance is to replace skylights when you replace the roofing, so you pay once for access and flashing and the warranties line up. If your roof is five years from replacement, weigh whether to wait.

How to choose

Check the framing before you fall in love with a spot: Rafter layout, trusses, ducts and vents decide what's possible. Ten minutes in the attic saves a redesign.
Budget the light shaft as its own line: On a flat ceiling, the shaft is a drywall and paint job. It's the most commonly omitted item in a low bid.
Think about orientation and heat: South- and west-facing units bring heat with the light. Match glazing to your climate zone using the NFRC numbers.
Pick venting only where you'll use it: It's about double the unit cost. Great in a steamy bathroom; often unnecessary in a bedroom.
Coordinate with roof plans: Doing skylights and roofing together avoids paying twice for access and flashing and aligns warranty coverage.

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FAQ

Skylights guides — common questions

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Where should a skylight go in a room?

Where the light is useful and the framing allows it. North-facing slopes give steady, cool light; south and west give more heat gain, which the glazing specification has to handle.

What is a light shaft?

The finished drywall tunnel between the roof opening and a flat ceiling. Splayed shafts spread light more; straight shafts give a narrower beam. Either way it's a real construction cost.

Can I put a skylight in a truss roof?

Not by simply cutting a truss. Trusses are engineered assemblies; modifying one needs professional design. A contractor who proposes cutting one casually is a hard no.

Fixed, venting, or tubular — how do I choose?

Fixed for light only and lowest risk. Venting where you want air, at roughly double the material cost. Tubular for small interior rooms where a shaft isn't practical.

Sources

Where these figures come from

Fixr — Skylight Installation Cost · retrieved 2026-07-26
ENERGY STAR — Residential Windows, Doors and Skylights Key Product Criteria · retrieved 2026-07-26
VELUX — How Often Do Skylights Need to Be Replaced? · retrieved 2026-07-26