Sizing a sill?

Ga Mtn Man · February 09, 2015, 10:27:00 AM

This isn't exactly a timber framing question but I hope you guys will offer some help anyway. I'm in the planning stage for a small cabin and I'm trying to figure out what size the sill needs to be. I'm going to use red oak for the sill supported by post and pier on 8' centers. The span of the floor joist will be 8' and the wall and roof construction will be standard stick framing. There will be diagonal bracing from the posts to the sill. I'm figuring on a 40 lb live load for the floor structure. Inspection is not an issue but I do want it to be sturdy and not sag over time.

Jim_Rogers · February 09, 2015, 03:40:21 PM

You need to figure the joist size first and the spacing of them so you can make the sill large enough to carry the load.

What type of wood will the joists be?

Jim Rogers

Ga Mtn Man · February 09, 2015, 06:03:40 PM

I was planning on using 2x8 white pine 16" OC for the joists.

Ga Mtn Man · February 11, 2015, 07:29:28 PM

Would a 4x8 red oak timber be large enough for this application?

Jim_Rogers · February 11, 2015, 07:50:10 PM

40 lbs live load is a bit lite but if that's what you think, then add 10 lbs dead load for the flooring and use that in the calculator to determine if a 2x8 pine would work.

Have you used the online load calculator in the red tool box?

Jim Rogers

Roger Nair · February 11, 2015, 08:12:43 PM

GMM, no one can answer that question without a plan complete with connection details. The perimeter beams will also pick up load from walls and roof. In the TF context, the joinery would require removal of fiber for housings and mortises, the devil is all in the detail. So in general, I look for the beams to be deeper than the joist if the joist and beam is on the same level. I want a fairly deep support under the notch. So I would start with ten inch deep beam and how thick can be adjusted to the depth of notch detailing and a minimum thickness to match the walls above. When calcs are done grade and species must be specified. That's how I'd define by context. Actual design calcs can be a whole different animal.