I don't have the NDS, but the American Wood Council's span calculator
at <http://www.awc.org/calculators/span/calc says the E of douglas
fir depends on the grade--1.6 for #2, 1.7 for #1, 1.8 for #1 & better,
and 1.9 for SS. Since the American Wood Council publishs the NDS, I'm
assuming they are using NDS values! I should buy a copy sometime.
Well, since our calculations use the E value ignoring "strength
reducing features" (timber people don't like the term flaws), and
these flaws will increase the deflection, I assume the tabulated E
value is penalized based on grade.
That's got to be overkill for 6 ceiling joists. If I ever add a 500
square foot second story, I'll consider engineered timber for the
floor joists that will interleave the existing ceiling joists.
BTW, the fact that higher E is achieved in engineered timber using the
same fibers as solid sawn lumber suggests to me that the flaws must
negatively impact E--I don't think it is all attributable to the glue.
But I don't really know anything about glues.
PS. Most the NDS tabulated values are something like the 5th
percentile values, as wood specimens vary in strength alot depending
on the locations of flaws. Thus the overstrength in practice can be
quite high, up to 4 times or more. The exception is the tabulated E
value, which really is an average. There is a separate published
E_min value, which is comparable to the other tabulated values as a
5th percentile (or something like that). For douglas fir the E_min is
1.2 or 1.3, I think. As I recall, the main time E_min arises in
calculations is just when considering buckling.
OK, here comes. The house is one story over crawlspace/basement, with
a hip roof. Here is some ASCII art that shows the plan dimensions and
the original location of bearing walls (B):
! ! 8'
26' !BBBBBBBBBBBBBBBBBBBBBBBBBBN !
! NBBBB! 17'
! N !
The 26' wide by 43' long part of the house has continuous full
thickness 2x6 ceiling joists. The rear 8' of the house has 2x4
ceiling joists. In this rear 8' area, I have removed the ceiling and
the bearing wall for the ceiling joists. I have also removed the
non-bearing wall (N).
Well, since the wall N is also gone, I'd have to design and install a
17' long beam as well as the 8' long beam over the former bearing
wall. That seems like a lot more work than installing 5 new ceiling
joists. I'm pretty happy with the solution of using 2x8s with end
As others suggested, in my neck of the woods 20' is a stock length.
As Rico mentioned, he does sometimes question our sanity on these
The taper or the end relief would work (IMO) with or without a plywood
Does a joist edge depth of 5" vs 5.5" really make that much different?
I'd cut the taper & be done.
I think Wayne's thinking about using single (notched) 2x8's OR
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