Cantilever(?) Wood Sill Plate 1

[JoshH726]

I was provided the attached figure considering for single story, lightly loaded (SDC A, 115mph wind) wood frame office building. My initial concern is uneven bearing stiffness between the concrete and insulation would lead to cantilever or cross grain bending in the sill?

This is similar to Figure 1 in the attached article I think pulled the picture from.

Let's say the minimum "stem" width of 3-1/2" to allow for a screw anchor, and would fit a washer. This would be a 2" "overhang" for the sill plate. Since the bearing stiffness is non-uniform below the sill plate, there should be a nonzero amount of bending in the sill?

Another issue appears to be if shear loads in the wall exceed 400 plf, I'd need the washer to be within 1/2" of the loaded side. This seems to then be the far side of the wall. So custom cut washers?

Anyone else seen a detail such as this? Any thoughts from field install?

Thanks in advance

 

[phamENG]

I didn't dig deeply into the article - thankfully that's not something I have to contend with much. Being in the mid-Atlantic, our climate is relatively mild. A single snow fall greater than an inch is usually enough to use up the collective snow removal budgets for all of the local municipalities for the year and, while our summers do get up there, it's usually only for a month or two that it's really hot. So there's not a big push for fancy insulation details. And when does pop up, it's usually pretty easy to negotiate the really silly stuff out.

dik - as for the needing 2x6 and 2x8, Josh and I were referring to the structural need. If a 2x4 would carry the structural loads, it doesn't really matter that it's a 2x6 as long as you detail your bearing on the top of the wall properly.

 

[dik]

In these environs... 2x4s went the way of the Dodo... all more the reason the detail is suspect and 'stands out'. Joe should have known that, as an authority. Last time I did a 2x4 wall was about 20 years back, near Lindsay. It was for a cottage... that was completely non-insulated and unfinished. Some interesting discussions with the AHJ on that... Client was a well off programmer dude that wanted a cottage like the one his parents owned when he was a kid.

[Added] With 2x6 and 2x8 framing, studs could easily be at 24" o/c... but still see them at 16... dunno why... the greater spacing is better for thermal transmission, too.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[JoshH726]

Step away from the last reply and was curious the number of additional comments this thread received. Climate in question would be Michigan, so 2x6 framing, which prompted the question.

Enable, are you able to provide the ASHRAE paper? I'm curious to know.

 

[Enable]

Josh: I don't have a copy of the paper as I am not a fellow but it can be downloaded for $8 ASHRAE Journal, Vol. 62, no. 5, May 2020

As phamENG notes if you are constructing a standard dwelling a 2x4 structure at 16" c/c would likely be sufficient for the loads and hence the detail is no issue (as the load can be safely taken by the ledge as detailed even with a 2x6 wall). I'm surprised dik brought up the switch from 2x4 to 2x6 but could not recall the reason that we did that was not for any structural reason, rather it was to increase the amount of insulation in the cavity. The only case where that is not true is in the event of relatively non-typical dwellings or where advanced framing is being used. Though he is correct in saying that continuous exterior-borne insulation wrapped around all elements is the ideal, which is in fact the position advocated by Joe. So if you can argue to get that it's a win-win for everyone!

 

[phamENG]

dik - if you're using batt insulation, 16" wide batts are usually the most common. Tighter or wider stud spacing will drive up labor costs for insulation installation.

 

[dik]

Thanks... didn't know if they come in 24" widths, or if there's a premium... don't do many houses...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

Just checked on R20 by Johns Manville there is about a 3% premium on 23" wide batts over 15" wide batts... not significant... drywall issues, or whatever... due to the greater spacing. Line up with roof trusses, though, but not likely floor joists.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[NorthCivil]

The best method would be to take that insulation between the footing and the slab and put it exterior to the wall.

if that cant be done, can the lower level wall be framed with 2x8s instead of 2x6s, then the footing can be cast 2" wider?