By width, do you mean depth? Rafters can be quite skinny so long as
they are deep and braced.
But then, I'm feeling a bit thick this morning and I'm supporting far
too much weight.
With a tenon joint, it's weight bearing properties depend on position
of the tenon in the joint - the tenon does not have to be the full
depth of the joint but the lower down it is on the joint, the more
of the depth of the rafter or cross-piece is available for bearing
load. Any shoulder on the bottom of the joint tenon negates that
amount of the depth of the beam. For instance, the second image here -
http://en.wikipedia.org/wiki/Mortise_and_tenon
- 'stub-tenon' with no shoulder at the base is load bearing for
furniture so that my ample rear does not meet the floor suddenly. The
depth of the tenon reduces torsion but it is the lower part that
takes the weight and a 'haunched tenon' holds the tenon in the
mortice better, preventing sag. So does a short top shoulder.
Ancient technique required a over-length through tenon locked with a
tapered pin through the stub of the tenon projecting through the back
of the mortice.
Andrew Fildes
afildes@xxxxxxxxxxxxx
On 28/03/2008, at 9:29 AM, Jeff Keller wrote:
> Chuck explained common US construction. The only thing I can add is
> that the width of the rafter depends upon it's length. The width
> prevents excessive bowing when weight is applied to the center of the
> rafter. It probably doesn't take a very large tenon to support the
> weight that typical toe-nailing will support.
==============================================
List usage info: http://www.zuikoholic.com
List nannies: olympusadmin@xxxxxxxxxx
==============================================
|