Green Renovation: Adding Skylights, Part 1

Jim Mallery

Part 1 of a six-part series, Green Renovation: Adding Skylights

If you are living in an old house, with its smaller windows and light-challenged rooms, you probably have thought many times about adding skylights.

New skylights are energy efficient and will flood a dark room with natural light, reducing your need to flick light switches on and off all day.

Maybe you have to reroof, so there is prime opportunity to add a light. It is a pretty simple process for the do-it-yourselfer. This first article will discuss some basic considerations.

With Skylights, Size Does Matter

First of all, size matters. Your rafters or trusses probably are on 2 ft. centers; therefore, a skylight that is 2 ft. wide will be easy to install. Sure, you may want the spacious 4 ft. x4 ft. skylight, but it is going to vastly complicate your project, because you will have to cut a rafter or truss.

If you cut a rafter/truss, your local building code probably requires you to double up all of the supports. That means double rafters/trusses on both sides of the skylight and doubled headers and footers. All supports would be made of at least the same size lumber as the existing system.

If you are going to be cutting a manufactured truss, you should have a truss expert engineer your modifications so that you are guaranteed the strength to carry the load.

But rather than do all of that modification, why not just go with two skylights sized at 2 ft. x 4 ft.? In this case, you would only have to cut holes in the roof and ceiling without having to add extra reinforcement other than a simple header and footer between two rafters/trusses. And the header and footer for the light would only need to be a single board--again of the same dimensions as the rafter/truss.

Old Houses: Special Skylight Considerations

If you are dealing with a really old house, you may have non-standard construction for your rafters. They may be centered at something other than 2 ft., or they may be under-engineered and on the dubious end of the strength continuum.

Even if your roof system is not frail, it may have had a second or third layer of roofing added, meaning it's at its load maximum.

You can deal with non-standard construction, but you might need some professional guidance so that you don't end up with a sagging or collapsed roof.

When you are working out all of your details, know in advance the framing size for the skylight you will install--almost all are designed to fit over standard, 2 ft.-center rafters/trusses. However, if your construction is non-standard, you can special-order skylights to accommodate non-standard sizes.

In part two we will look at choosing skylights for energy efficiency, as well as explore types of skylights, placement and costs.

Adding Skylights, Part 2

About the Author

Jim Mallery, a semi-retired journalist and onetime registered contractor, has extensive experience remodeling, repairing, and rebuilding homes.

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