Over hanging wall plates?

[rwalter]

Hello Everyone,

I have a question that hopefully some one out there can answer. First off I am building a 20x32 1 and ½ story cabin and I have built a foundation that is 4" short on each dimension. The reason I done this is that I have installed 2" Dow Square edge polystyrene insulation on each wall. This brings each wall back to size and the true 20x32 dimension. I was planning on cantilevering my floor joists 2" to compensate for the difference above the foundation. However I was talking to a contractor and he recommended me keeping my rim box square to my foundation and instead overhanging my wall plates by the necessary amount The advantages being you don't have to insulate each cavity on the inside of the rim joist since you can run the exterior polystyrene insulation right up over the outside of the rim joists.. Now I am using 2x6 walls so if I don't use any foam insulation on the outside of my sheathing my plates would over hang by 1 ½ inches (1/2" plywood would make up the rest of the dimension to bring it back to "square"). This should leave me with around four inches of width of my wall plate sitting on the deck if I do it this way. I could also add foam insulation board to the outside wood framed walls and that would move the decrease the overhang of the plate by the thickness of what ever dimension the foam board was. So what amount of overhang is acceptable and structurally sound?

[PEG688]

 rwalter  I'll answer but still have questions , like where is the cabin located , cold / warm area ??  Will it be inspected ??    If I was shorted foundation  in my world , I'd # 1 Have a word with my foundation man. # 2 I'd put on a wider PT sill plate so my overhang would consist of a over hanging sill plate then my box sill as normal on it .  I'd insulate the joist bay / basement / crawl area with batts to get the R-30 needed in my area of the counrty , ridged foam is only going to get to maybe a 9 R or 10 R value in 2 inch , the pink stuff we have in these parts anyway , maybe someone / some where it can be a bit more , not sure on that .    The other issue to the ridged stuff on the exterior of the foundations is protecting it from weather, weed eaters , etc when we use it , very seldom , we have a flashing made to cover it with a beveled bend to shed water , So it's sort of a added step / failure point and" not very good insulation" R value wise.          Hope that helps , good luck , HTBH  ;)PEG      Only time I've ever cheated with overhanging plates was to compensate for poor , foundations work or using old / existing slabs on foundation and that never got to more than say 1 1/2"   for short runs , not the whole works .   I know you can cant the joist if you enclose the resulting soffit .   The project PT sill would do that .

[rwalter]

PEG688,

Its being built in Western NY and yes it will be inspected. The contractor who suggested this method  is the mason who layed the foundation. He suggested it before he put the foundation in. He stated thay he has uses that method frequently. I was planning on doing that with the sill plates and that actually is the model for conditioned crawl spaces that they recommend at Building Sciences when using exterior foam insulation. I

http://www.buildingscience.com/resources/foundations/conditioned_crawl.pdf

It was at that point when I was talking to the mason about my plans when he suggested this alternative method.

Thanks for the response.

[glenn kangiser]

According to Ken Kern, normal 2x4 stud walls are way overbuilt as far as strength goes, so I would think that if a 2x4 width is bearing it would be more than adequate.  It sounds as if your mason is familiar with this system and seems to make sense.

[John Raabe]

Yes, you can easily cantilever the 2x6 wall plate the 2" as you suggest. I have used the same detail in many of my plans. It simplifies the foundation and rim insulation.

Normal house framing dimensions are from outside of rough framing. So you wouldn't normally count the sheathing or siding in the layout dimensions.

[PEG688]

I'd only add that if , and it sounds like you do , have a approved set of plans issued and you start right off by changing the type of foundation system from a "conventional" vented to a newly tested system . You'll be doing a lot of "Esplannen , Lucy " to the inspector .  If that system is common in your area , which it sort of sounds like, you might be ok , if you continue to make random changes and the insp . has to look up evualuate each step , / insp . cycle he'll get testy learnin  on ya . Lidget changes/ questions are one thing,, redesigning as you go , out here gets more trouble than it's worth. Remember "Argueing with a building inspector is like wrestling with a pig , you both get dirty and the pig likes it ."   And you still need some type protective flashing to cover the foam   Good luck, HTBH  ;)PEG

[rwalter]

John, Glen and PEG68

Thanks for the replys. PEG688 yes its part of a designed system for a conditioned crawls space and actually the building inspector and the mason that put down my foundation know each other very well. The building inspector really didn't even worry about inspecting the footer or the walls before back fill yet which I hope to be ready for Friday. When I called him today to tell him I'll be getting ready to back fill soon and he said "well I'll try to make it buy but just go ahead and do the backfill if you need to". The mason I hired is has been doing foundations for 35 years in this county and I guess his reputation stands on its own. I guess thats one advantage of being out in there country. Everyone knows everybody and whats going on with everyones business. I guess I'll over hang the plates on the wall since it will allow me the additional insulation factor on the outside, plus still allow me to super insulate on the inside which is required by design anyway.