Installing a Round Window

Framing for a round, octagonal, oval, or half-round window starts the same as for a standard window. Cut and frame a rectangular opening to accommodate the window at its greatest dimensions -- in this case the top of a half-round window's arc.

The installation of the round window shown here includes sheathing with self-adhesive flashing tape. There is no metal drip cap over the rounded top; the joint between the curved brick molding and the siding is simply caulked. For a more weatherproof installation, have a roofer or a sheet metal shop make up a curved drip cap to fit your window.

With a flanged window like the one shown, it often makes sense to remove a section of siding so pieces that overlap the flange can be woven in.

For curved cuts through heavy materials, a reciprocating saw is nearly indispensable. You can rent one if you don't own one.

Prestart Checklist

Time
With a rectangular opening cut, about 3 hours to frame and install a half-round window

Tools
Tape measure, hammer, drill, scribing compass, reciprocating saw, circular saw or power miter box, stapler

Skills
Measuring; framing; using a circular saw, jigsaw, and reciprocating saw

Prep
Cut and frame the opening on the inside, but do not cut the sheathing.

Materials
Round-topped window, cardboard for a template, 2x4s for angled framing pieces, roofing felt or building paper, self-stick flashing tape, nails and screws