What are the best skylights for a pitched roof?
Short answer. On a pitched shingle roof, the best choice is usually a deck-mounted skylight installed with the manufacturer's step-flashing kit, which ties into the shingles and underlayment the same way a chimney or wall does. Curb-mounted units suit low slopes and some metal roofs, and tubular skylights come with flashing bases designed for a range of pitches.
Deck-mounted vs curb-mounted
- Deck-mounted. Attaches directly to the roof deck with a low profile. Its flashing kit includes step flashing pieces woven with each shingle course plus head and sill flashing, usually with a self-adhered underlayment collar. Most deck-mounted units list a minimum pitch, commonly around 3/12, so check the specifications.
- Curb-mounted. Sits on a wooden box built on the roof and flashed like a small chimney. Better for low slopes, some metal roofs, and replacing older curb units without reframing.
Placement on a pitched roof
- Keep skylights out of valleys and away from places where water concentrates, such as below a dormer or a long run of roof feeding into one spot.
- Stay a few feet below the ridge so the head flashing has room to tie under the courses above.
- Fit the width between rafters or trusses where possible to avoid structural changes.
- On steep pitches, a taller skylight gives a better view and more light. On lower pitches, a wider one spreads light.
Roofing type matters
Flashing kits are made for specific roofing profiles. Shingles use low-profile step flashing kits. Tile and some metal roofs need high-profile kits or curbs. Using the wrong kit is a common cause of leaks.
Underlayment around the unit
A self-adhered membrane collar wrapped up the sides of the frame and lapped correctly into the surrounding underlayment backs up the metal flashing. This is where careful roofers spend their time.
Timing
Skylight flashing usually wears out with the roof. Replacing or reflashing skylights during a roof replacement avoids tearing into new shingles later.
See replacing skylights with a new roof, roof flashing explained, and common roof leak causes.