What size skylight do I need for my room?
Short answer. A widely used rule of thumb keeps skylight glass to about 5 percent of a room's floor area if the room already has plenty of windows, and up to about 15 percent if it has few. In Georgia's heat, stay toward the low end, especially for skylights facing south or west, because too much glass overheats the room.
Working the numbers
- A 12 by 15 foot room is 180 square feet. At 5 percent that is about 9 square feet of skylight; at 15 percent, about 27.
- A nominal 2 by 4 foot skylight is about 8 square feet, enough for a well-windowed room of that size.
- A 60 square foot bathroom needs only a small unit or a tubular skylight to feel bright.
The glass is a little smaller than the rough opening because of the frame, so treat these as approximate.
Adjust for the room
- Hallways, closets and interior baths: benefit the most; lean toward the higher end or use a tubular skylight.
- Kitchens: good daylight over counters, and a venting unit helps clear heat.
- Bedrooms and media rooms: consider smaller units with blinds, since early sun and glare can be a nuisance.
- Vaulted ceilings: the skylight sits close to the room, so a smaller unit goes further.
- Flat ceilings under an attic: light travels down a shaft, and a shaft that flares wider toward the ceiling spreads light better than a straight one.
Adjust for orientation and heat
North-facing skylights give steady, cooler light. South and west faces bring heat in Georgia summers, so choose low-e glass, consider a shade, and keep the size modest. Tubular skylights deliver useful light with very little heat.
Several small or one big?
Two smaller skylights often spread light more evenly than one large one, and smaller units fit between framing without structural changes. See skylights and roof replacement and attic heat and shingles.