Rafter Layout with Log Timbers
Placing the Measuring Line
MEASURING LINE AND WIDTH OF MATERIAL
Measuring from the edge determined to be the upper surface of the rafter, and at the wide end if you are using poles or logs, find the diameter or width of your material. See Drawing #11. This is at best an approximation due to the shape of a log, but it is perfectly acceptable for our purposes.
If you are using finished or rough cut lumber it is a simple matter of measuring the width of your material.
Divide the diameter of the wide end of your material by 2, as in 6 divided by 2, which would give you 3 inches. This is the distance the measuring line will be from the top edge of the rafter.
If you are using lumber this is the figure you will use on all of your rafters.
If you are using logs, which are rarely of uniform dimension, you must measure all of your material first and then determine a figure that will work on all of your rafters and not penetrate over half way through your material.
Using the same figure on all of your rafters assures that you will have an even surface upon which to nail your roof boards, even when your material is of varying thickness.
The placement of the measuring line also determines how far the seat cut will penetrate your material. Ideally, the notch you cut out for the seat need not be any larger than the wall plate it will rest upon. This provides the maximum load bearing surface. However, you do not want to cut over half way through your rafter material either, for this will reduce the strength of your rafter as it extends beyond the wall for your eaves. Half way is a good place to start.
Once this figure is determined, measure from the UPPER SURFACE OF THE RAFTER, or the edge closest to you, toward the opposite edge and mark the log/board at both ends. See Drawing #12.
USE THE CHALK LINE REEL TO MARK THE LINE
The next step is to snap a chalk line between these two points, as in Drawing #13. If you have never done this before it may want to take a couple of practice shots before you do this on the log where you really want your measuring line. My best advice is to stretch the chalk line tight. On logs it helps to remove bumps or stubs of branches which may deflect the chalk line as it strikes the log.