Install a Skylight 9 - Opening the Ceiling Install a Skylight 9 - Opening the Ceiling

After you've secured the skylight, you can cut, frame and finish the ceiling opening any day, rain or shine. And you can begin enjoying the light streaming in through your skylight even before you've completed framing and finishing the hole in the ceiling.

Cutting the Ceiling

Since you planned and marked the ceiling as the first step in installing your skylight, cutting the opening is fairly straightforward.

Check your Markings

Even though you marked the corners and center of the ceiling opening before cutting through the roof, it's a good idea to double-check your marking against both the framed roof opening and the angle of the light shaft.

Check the corner nails and replace any that are missing. Stretch your chalk line around the four nails and snap the line between each pair of nails to mark the opening. Then remove the nails.

Marking the Cut

Before you cut the opening, cover the floor and the furniture below with a large tarp and drop cloths. Wear a painter's mask and goggles to protect against the dust while you're cutting. Cut through wallboard (gypsum board) with either a keyhole or reciprocating saw. Cut lath and plaster with a reciprocating saw fitted with a coarse, wood-cutting blade.

When you come to a joist, cut through only the wall board to prevent tearing when the ceiling cutout is removed. Ceiling material is quite heavy, so you'll want to cut it out in small pieces if the area of the opening is larger than you can conveniently handle.

After the opening is cut, break off the wallboard and remove the wallboard nails.

Cutting Ceiling Joists

Before you can cut the ceiling joists, you'll need to reroute any pipes, wiring or air-conditioning ducts that cross the ceiling opening, if you weren't able to plan around them.

If you have to cut one or more joists that are more than 30 inches from a wall you need to support them before you cut. Using 2 by 4 lumber, cut two pieces long enough to span both the opening and two joists on each side of the opening. Position the pieces at least 12 inches from the edges of the opening, and fasten them with woodscrews to the joists. This will keep the joists from shaking and jiggling when you cut through them, and will prevent nails in the wallboard from popping loose.

To cut joist, follow the instructions for cutting a roof rafter, with these additional guidelines: if you're planning a straight light shaft, cut the joist at a right angle to the ceiling; mark the angle of cut for an angled or splayed shaft with a straightedge or a length of string positioned between the bottom of the joist and the roof opening. Be sure to allow for the headers by measuring out from the opening.

Framing the Ceiling Opening

Using joist-hanger nails, nail the hangers to the joists. Set one header into each facing pair of hangers and nail it to the cut end of the joist with 8-penny common nails. Fit the second header into each set of hangers and attach it to the first header with 16-penny common nails driven in a staggered pattern. Nail the joist hanger flanges to the headers. Repeat on the opposite side of the opening.

If your ceiling opening doesn't fit exactly between two joists, you'll need to install additional framing members parallel to the joists, along the edge of the opening.

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