Sills, solid vs laminate

[Arky217]

Soon to start CSMilling some Southern Yellow Pine for foundation sills.
They will be 6"x8"x12' on 6' span piers.
What would be the upside/downside of using 6"x8"s solid cants versus nailing together (3) 2"x8" or (4) 1.5"x8" pieces ?

Thanks,
Arky

[glenn kangiser]

I myself would use them interchangeably  especially if the separate ones were well nailed and glued.

I would expect a bit more warpage and cracking possible out of the single one but they usually don't consider that to be a problem.  It shouldn't have much warpage if nailed up right away and not drying loose on it's own unrestrained.

[PEG688]

 I'd call them beams not sills , sills generally sit on concrete or cinder block type foundations.

Yours are truly beams.

Solid beam IF milled then put right into use will shrink , and quite possibly twist if not dryed properly.

Same thing goes for sawning smaller and not allowing drying time. Which as a general rule of thumb is one year per inch of thickness.

That being said I know Glenn cuts and uses his stock .
And if checking , shrinking and twisting can be lived with this may not be a issue for you.

Also IF you can build fast enought the "greater" assembly may reduce the twisting some what.

So, as usual,  "It Depends" on factors you did not fill us in on.   This is not uncommon,  so can you expand on some of the  "other" factors I touched on? 

Glenn will add to this I hope. 


Edited to add : I see Glenn's already on the job / thread.   

[glenn kangiser]

Believe PEG first then me. 

I will add that many of the things I build such as timber frame cabin, shops, out buildings could take a lot of warpage or shrinkage with no problem.  You need to decide how critical your application is.  I find softwoods to shrink about 5/8" per foot of width and warping is variable depending on the area of the log the beam is cut from as well as the particular features of the tree it came from.

[Arky217]

Well, if I make the sills (or beams if you prefer) one piece, they would be pith-centered from the logs to minimize warping. Either way the sills would be sticker stacked to air dry until I have finished milling all of the framing lumber. (This is for a 26x48 dwelling)
If solid 6x8, one advantage would be less milling, but they might not be completely air dried by the time I'm ready for them.
If planks, they probably would be down around 20% mc, and easier to handle, but would require more milling and the effort to fasten them together.

As far as strength, I've heard it both ways. I've heard several say that the solid piece would be stronger, but according to the span program that I use (an Excel spreadsheet program called powerspantablelite.xls), the planks would be much stronger. For example, the program shows that a beam spanning 6' supporting 12' joists on both sides with a live load of 40psf and a dead load of 10psf, a 5.5"x7.5" beam would have a bending overdesign of 17% whereas just (3) 1.5"x7.5" planks together (total 4.5" width instead of 5.5") would have a bending overdesign of 49%, and that's just side by side, not glued or even nailed together.  (go figure ?)

Anyway, I'm leaning toward the solid sills, mainly because of quite a bit less milling.
Anyone think this might be a major mistake ?

Thanks,
Arky

[glenn kangiser]

I think that is what I'd do, Arky- I have a mill also and a fairly liberal tolerance spec. (My Own)