Free homeowner tool
Skylight count and size
How many skylights and what size. Enter the room and how much light it gets now — we handle the roof side.
Skylights, for planning
Enter the room size to see how many skylights it takes and what size.
Impact rating, approvals and how it mounts
A skylight is an opening in the roof, so in Florida it needs a Florida Product Approval and, in Miami-Dade and Broward (the High-Velocity Hurricane Zone), a Miami-Dade Notice of Acceptance. Where opening protection is required, that means an impact-rated unit. Verify what your city's building department requires for your address.
Curb-mounted units sit on a raised frame — the usual choice on tile, metal and flat roofs, and for replacing an existing curb skylight. Deck-mounted units fasten directly to the roof deck with a flashing kit made for the roof covering, which is common on shingle roofs. Either way the flashing kit, not sealant, is what keeps it dry.
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How the calculator works
- Step 1
Size the daylight
A common planning rule: skylight glazing of about 5 to 10% of the floor area lights a room with few windows well; 3 to 5% is plenty where there are already windows.
- Step 2
Divide by the unit
A 2×4 skylight has about 8 sq ft of glazing, a 4×4 about 16. Tubular skylights are rated by the floor area they light instead, so for those we count by room size.
- Step 3
Choose the type
Fixed units are light only. Venting units open to let heat out of a kitchen or bath. Tubular units fit where there is no room for a shaft.
- Step 4
Plan the roof side
Impact rating, product approval, curb or deck mount and which slope it sits on decide how well it works and how long it stays dry.
Planning a new roof at the same time? Estimate the roof by squares and material, or read about our skylight work.
Skylight questions
- How many skylights does a room need?
- Usually one or two. The tool sizes the glazing to a share of the floor area — more where the room has no windows — and divides by the skylight size. A 180 sq ft kitchen with windows comes out at one 2×4 unit; an interior bathroom often wants a single tubular skylight.
- Do skylights have to be impact-rated in Florida?
- Where the code requires opening protection for your address, yes — a skylight is an opening in the roof. In Miami-Dade and Broward the unit needs a Miami-Dade Notice of Acceptance; elsewhere in Florida a Florida Product Approval for that use. Your city's building department can tell you what applies to you.
- Curb-mounted or deck-mounted?
- Curb-mounted skylights sit on a raised frame and are the usual choice on tile, metal and flat roofs, and whenever an existing curb skylight is being replaced. Deck-mounted units fasten directly to the roof deck with a flashing kit made for the roof covering, which is common on shingle roofs. Either way it is the flashing kit, not sealant, that keeps it dry.
- Will a skylight make the room hotter?
- An old single-pane unit will. A modern unit with low-E glazing lets in far less heat, and placement matters — a north- or east-facing slope gives soft light without the afternoon load. We talk through where it goes before cutting anything.
- Is it cheaper to add skylights during a re-roof?
- Yes. The roof around the opening is already open and the flashing is being done anyway. If you are planning a new roof, it is the time to add or replace skylights.
- What does a skylight cost?
- We price it at the free estimate, in writing, after looking at the roof — roof type, pitch, how long the light shaft is, impact rating and the specific unit all change the number. The tool gives you the count and size so the estimate starts from the right place.
Get a free skylight estimate
Tell us the room and the roof type. We look at the slope and the attic above it and give you a flat rate price in writing.