How to Make Log Rafters

Review the design of the structure's roof. Determine the pitch and rafter length from calculations based on the height of the attic and the structure width. The vertical distance down from the ridge board to the top of the wall studs is the attic height. Note that the ridge board is the top, on-edge board, running the entire length of the roof, to which the rafters connect. Write down the lateral distance from the outside edge of one wall stud to that of the opposite wall. Divide this number by two and record this as side number 1. From the planned or designed overall height of the structure and the height of the wall studs, calculate the attic height. This is the vertical distance from the rooftop to the level of the upper surface of the wall studs. Record this number as side number 2. Square both side numbers and add the products together. Take the square root of the total and this is the length of the rafters.

Take the first log and verify that it is longer than the intended rafter length. Measure and mark the plumb cut, which is the 45-degree, downward slanting cut at the top end of the rafter. The resulting flat, true and plumb vertical surface is nailed to the side of the ridge board when the roof is constructed.

Make the plumb cut with a chainsaw or circular saw.

Construct a temporary roofing structure jig by nailing a 2x6-inch board reaching as high as the top of the ridge board will, with a horizontal, on-edge piece of 2x6 as the simulated ridge board.

Lay the end of the rafter log against the flat side of the temporary ridge board. Nail the top of the rafter log to the flat side of the temporary ridge board.

Extend the rafter log attached to the ridge board downward and lay it up against the side of the top of the wall stud. Scribe the birds-mouth cut, which is the 90-degree cut from the inside surface of the lower end of the rafter. That cut enables it to sit levelly on the top of the wall stud.

Use a chainsaw or hand saw to make the birds mouth cut. Test the cut's square and level lines by placing it on the wall stud.

Measure and scribe two 45-degree cuts that intersect at the center of the log, making a pointed end on the log. Use a chainsaw or handsaw to make the cuts.

With the rafter log sitting in place, hold a length of 2x6 board against the side of the rafter log with one end even with the top of the ridge board and the other end 4 inches above the outer edge of the wall stud. With the 2x6 touching the rafter log, scribe a line along the rafter log that matches the upper edge of the 2x6. This is the cut-out dimension of the log removal section that results in a rafter that will support flat and true roof sheeting. All the wood above the scribed line will be removed.

Take down the rafter log, lay it across two sawhorses, birds-mouth cut-side down, and put wedges underneath both sides of the log. Use a draw-knife to remove the cut-out wood that takes the rafter log down to the desired level. The resulting, finished log is the template for all the other rafter logs.