How to Build a Wider Attic Rafter for More Insulation

Increasing rafter width adds depth to the ceiling cavity, allowing you to install thicker layers of insulation and reduce temperature loss. Wider rafters are particularly important for bulky insulation materials, such as fiberglass rolls or batts. Although you squash fiberglass to fit more within the rafters' cavities, it won't increase the material's insulation value. To make a deeper cavity, laminate pieces of wood onto the rafters' exposed edges. This process is called "furring out," a reference to the name furring strips, which is the material you'll use to build up your roof framing.

Tape measure
Pencil
Furring strips, usually 2-by-2
Circular saw
Nail gun
8d gun nails

Instructions

- 1
  Stretch a tape measure from the rafter's connection with the wall plate to the rafter's connection with the roof's ridge board. If the length of your furring strip lumber exceeds the length of the rafter, mark the length of the rafter on a furring strip and cut it to size with the circular saw. If the rafter's length exceeds the furring strip's length, split the length between two or more pieces, mark the pieces and cut them to size with the circular saw.
- 2
  Load a strip of 8d framing nails into the nail gun. Lay the furring strip flush against the rafter's top edge. Butt the strip's end against the joist that intersects that rafter at its connection to the wall plate. Align the edges of the furring strip with the edges of the rafter. Beginning at one end of the furring strip, drive a nail through the center of the strip and into the top edge of the rafter.
- 3
  Drive nails through the furring strip every 6 to 8 inches until you reach the opposite end, checking the alignment of the strip's edges as you progress. If your rafter requires additional furring strips, butt the second strip's end against the end of the first strip and align its edges with the edges of the rafter.
- 4
  Fasten the second strip using the same nailing pattern as the first. Install successive strips in a similar manner until the end of the final strip butts against the rafter-to-ridge connection. Measure, mark, cut and fasten furring strips for the remaining rafters. If you are installing ceiling insulation, apply furring strips to the tops of ceiling joists.

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