Uninstalled square or rectangular skylights, whether dome or flat-surface types, can cost up to $2000 each if they have venting and shading capabilities. Some of the newer models also have special inner channels for catching condensation, not to mention having motor-driven vents and shades (these are very expensive). Thus, for certain home owners who want at least one plain skylight, it is more practical for them to make their own new or replacement ones.
Since this article if for do-it-yourself (DYI) people, it gives only the basic materials and processes for making and installing a two-foot square flat-surface model, leaving any size modifications, the tools used, and other details to their own expertise.
Materials and cost (assuming a ceiling-to-roof skylight chute is already in place).
- one 96-inch 2×4-inch pressure-treated board (for making a 3.5-inch high curb frame, $4); note: the so-called 2×4-inch board is really 1.5×3.5-inches
- two square pieces of 0.22-inch thick clear or frosted Plexiglas: (1) the topside one, 24.5-inches square; and (2) the underside one, 20.75-inches (about $25 each depending on availability)
- twelve or more #8×1-inch wide-head drywall screws (for attaching the topside Plexiglas to the curb frame)
- one 96-inch long piece of quarter-inch square molding or similar ($3)
- thin-metal aluminum counter or step-flashing strips if wanted ($10-20); note: a high-quality caulk can be used instead
- one standard gun-size tube of long-lasting acrylic caulk similar in color to the roof ($4)
- sufficient nails or screws for attaching the molding to the curb and for attaching the curb to roof sheeting or underlayment
- one quart of paint of selected color
Construction and placement.
1. Cut the 2×4-inch board into four pieces: two 24-inch long ones and two 21-inch ones.
2. Assemble these pieces into a 24-inch (outside to outside) upright square curb frame with eight 2.5 to 3-inch screws, two at each corner.
3. Cut and attach the quarter-inch molding flush to the inside bottom of the curb all the way around its 21-inch inner square. This molding will hold the bottom-side 20.75-inch square piece of Plexiglas which will act as a condensation shield on the underside of the curb frame.
4. Paint the frame inside and out, matching the colors as desired similar to the chute walls and/or to the shingles. Let dry.
5. Clear a 24-inch square area over the open chute by cutting back any shingles and tar paper to this size.
6. Place the dry frame center over the chute, letting the shingles fit fairly snugly around the outside of the curb.
7. Slant nail or screw the frame to the wood sheeting of the roof.
8. Clean and place the 20.75-inch Plexiglas into the bottom portion of the curb frame where it will lie on the molding.
9. If wanted, flash or step-flash the outside of the frame (these strips are woven under or within the shingles starting at the lower end of the tilted curb frame). Let the strips cover the outside of the curb up to its top surface where it is snipped flush to that surface. Otherwise, caulk the shingles to the outside of the curb to prevent rain leakage around it.
10. Clean and place the 24.5-inch Plexiglas centered over the curb top. A small lip will hang over the outer edge of the curb.
11. Drill 12 evenly spaced screw slightly oversized holes around the edge of the Plexiglas over the curb itself, but not into it.
12. Screw 12 wide-head drywall screws through these holes into the curb, snug, but not overly tight.
13. Seal the top Plexiglas to the curb and/or its flashing (under the lip) with long-lasting caulk.
14. If needed, paint the flashing.
The thin-metal flashing of vent pipes, chimneys, and other items protruding through roof tops is the professional way to seal the roof around them. This procedure also eliminates the need to paint the outside of the skylight curb. However, today’s long-lasting caulks are dependable sealing materials. They can be used instead of or in combination with the flashing used. This caulking also saves on construction time and materials cost.
Also, if the thick topside Plexiglas cracks for any reason, like, from large hail or flying debris, it can easily be replaced with another piece from a nearby hardware outlet. This replacement cost is about one-tenth of that for a new skylight top. For more information on the DYI making and flashing of a skylight, see these sites.