Building the Traditional Hewn-Log Home

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Continuing with our example of a 20' end-wall length and the 10' roof height resulting from a 1:1 pitch, rafter length would equal the square root of the sum of the 10' ridge height squared (100) plus the 10' halflength of the end wall squared (100 + 100 = 200)-or a tad under 14' 2". (Rafter lengths can also be calculated from a scale stamped into most good framing squares; ask an experienced carpenter to explain how it works . . . and then you can forget you ever heard of the formula we just went through.)

The rafter length (Z) derived from the formula represents the distance from the ridge (the top of the rafter splice) to approximately the center of the plate logs. To determine total rafter length, add the amount of overhang you want for the eaves to the 14' 2" derived from the formula. If you opted for 2' eaves, for instance, total rafter length would be 16' 2".

RAFTERS ROUND OR RAFTERS RECTANGULAR?

You can, if you wish, ignore tradition and economy and push the building project to a speedier conclusion by using milled lumber for rafters. The only place this lapse in tradition will show is along the undersides of the eaves—which can be boxed in to hide your sin. But Peter, old-fashioned fellow that he is, prefers the traditional method of cutting 5"-diameter (or thereabouts) poles for rafters.

He works two poles at a time, milling or hewing their tops flat. After sawing the poles to length, he cuts lap-notches in the tip ends of the pair (the diameter of one pole determines the depth of the notch for the other, and vice versa), fits the joint together, and bores a 3/4"diameter hole through the center of the lap. When the rafters are erected on the roof, he pegs each matched pair together with a handcarved hardwood dowel driven through the hole in the lap-splice. Countersunk 1/2"-diameter bolts can be used in place of wooden pins if you prefer.

WHERE RAFTERS MEET PLATES

Another advantage of a 45° roof pitch is that it takes a lot of the mystery out of joining rafters to plates. The simplest joint is made by cutting a 90° triangular notch in the underside of each rafter so that the resulting inverted V fits over the outer corner of the plate. The joint is made fast by driving a spike through the rafter and into the plate log.

Peter uses a more complex "locking" joint, in which the bottom of each rafter receives a rectangular notch with its lower edge extended in an arc. In position on the roof, the upper corner of the notch in the rafter's underside forms a (male) V that points straight down and fits into a matching (female) notch in the plate.

The plate notch for this locking joint is trickier yet. First, two parallel chalk lines are snapped along the plate's top as a means of aligning the rafter notches. A V notch is then cut between the two chalk lines, so that the male V (the top corner of the notch in the underside of the rafter) fits into the female V in the top of the plate log. The outside edge of the plate notch (from the outer chalk line out) is beveled at 45° to match the slope of the rafter. As with the single-notch system, the rafters are spiked to the plates with large nails driven through the joints.

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