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Context: I am considering adding 2 skylights (22.5in x 23in)in my dining room. The attic space is very tight and I have only one option so that the skylights are almost centered on the ceiling below. If I use one, it will be off-center. Two makes it almost centered. The rafters and joists are on 24in on center.

Question:

Is it possible to place 2 skylights, side by side, separated by one rafter? That rafter will be shared as a support for both skylights, right between them.

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    You might consider solar tubes instead. If you don't actually care about seeing the sky (most of us don't gaze out our skylights), they bring in a ton of natural light and don't require as much space.
    – isherwood
    Jan 16, 2023 at 21:33
  • You know that with a bit of framing, you can have a skylight of your choice dead center, right? Jan 17, 2023 at 0:36
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    @AloysiusDefenestrate the permit is allowed for (2) 22.5x23 skylights. I will contact to the city to see if I can combine them into one. Also, the area where I want them is very tight and has purlin and a beam crossing perpendicular to the joists. I could do a bit of framing, but seems "difficult".
    – Max
    Jan 18, 2023 at 17:50

4 Answers 4

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The issue isn't with load, but with sealing ability. The light is made to go between rafters 24 inches on center. However, outside on the roof, the sealing flanges may need more than the distance between the 2 lights to be sealed properly.

This question needs to be asked of the manufacturer of the skylights.

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    You hit on the key point... Ask the manufacturer. Some make "combination flashing" for this purpose.
    – isherwood
    Jan 16, 2023 at 21:32
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That could be a problem. The skylight need sealing space around them

Thus having one rafter thickness as space between them might be a problem.

The weight is not the problem but sealing and the boxing might be tight.

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Sealing between them in what might be a one inch gap will be tricky.

There are "multi pane" skylights for this purpose that have manufactured framing over the intermediate rafter(s) but are actually one unit that only requires flashing and sealing around the outer perimeter.

You could fake this with a single larger unit that just floats over the middle rafter, though it might look funny. You could hide this with a light well. Keep the ceiling in place, build a second skylight in the ceiling, with a translucent lens covering it, and box in the space between the two skylights with the inner walls of the box painted white.

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That should be fine. I have definitely seen similar setups. The issue of rafter support is not really for the skylight itself - the weight of the skylight shouldn't be that different from the roof sections it replaces. The key is to support the roof in general and also (in colder areas) snow load.

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