Are these walls strong enough?

[bkrahmer]

I'm hoping someone can verify something for me. I'm designing my house, and I'm unsure about some framing details. The house is a 2-story gambrel with a basement. The dimensions are 32x37 (ridge line along longer dim). That gives me roughly two 16-ft spans for the main and second floor floor joists. I'm currently planning on butt-jointing the floor joists (2x12), secured with plywood gussets. I've got interior walls running right down the center of the house on the main floor and the basement for supporting the floor above. The main floor will have 3x 4' openings, roughly evenly space, with the basement having 2x 4' openings. Will standard 2x4 walls handle the job in both cases, or will I need some posts and beams or maybe 2x6? Also, should I spec a slab reinforcement (thickened to 12"?) under the basement load-bearing wall? Thanks! :P

[Rich]

I don't suggest butt jointing the floor joists. This only gives you 1-3/4" of bearing on a 2x4 wall and 2-3/4" bearing on a 2x6 wall (the 2x6 wall would be better). I always try and keep at least 3" of bearing if I can. You could overlap these joists by a couple feet. You also might want to look into TJI floor joists (Silent Floor system) you will end up being much happier with the performance. With TJI joists you would have a single joist that goes the whole distance across your house and bears at the mid-span on the wall - then you could probably get away with a 2x4 wall. You will most likely need web fillers at the mid-span and blocking along the top of the wall.
I think it's a good idea to put in a footer or at least a thickened slab under the supporting basement wall, as you mentioned.
You will need some type of built-up beam for the headers - 4' openings I would suggest 2-2x8's with 1/2 filler to flush out the header with your 2x4 wall. I would have a 2x6 wall in the basement instead of a 2x4 wall. For the 4' openings in that wall use 3-2x8's with 1/2 filler.
As a suggestion - talk with an architect and engineer before you complete your design. It's money well spent in my opinion - if for nothing else than approving header sizes and spans etc.

[mjpliv]

With regard to your question about the floor thickening - yes! To qualify as a bearing wall it must be supported. Different areas have different building codes. For example, in my aera I would not be allowed to just "thicken" the floor to 1' because the footings must be inspected before I can pour the floor. In the case of a "slab on grade" foundation the whole shootin' match would have to be engineered as a monolithic slab.

Check with the local building authority with regard to minimum requirements and if there are none - I would at least thicken the floor to a depth of 1 foot below the underside of the proposed slab

[bkrahmer]

Thanks for the very informative replies! TJI does seem like a very good way to go. I'm strongly considering it. 2x6 on the basement wall also seems like a good idea. Instead of a thickened slab, I like the idea of a footer as well.

For good or bad, there is no building department where I'm building. (Bonner county, ID) There is no inspections. You get a Building Locate Permit (which I'm planning on applying for tomorrow), and off you go...

The only thing I have left that I need checked is my gambrel roof trusses. I know of an engineer that I'm planning on running them by.

Thanks again. cheers

[Rich]

No inspections would be nice in some cases... in other cases it's sure nice having them sign off on stuff to.. CYA

[mjpliv]

Its a funny thing, every structure here requires a building permit which requires detailed plans (four elevations, sections, footing/foundation plans, plot plans/grading proposals and material summary). These plans are subject to a review by the building inspector(s), municipal engineers as well as development officers to verify they comply with federal. provincial and municipal code and bylaws. We have separate building authorities to inspect plumbing and electrical installations (once for underground portions, once at roof tight and once for final inspection) and if we are building an apartment building, the fire inspectors get involved.

During construction we have a footing inspection, pre-backfill inspection, framing (rooftight) inspection, pre-drywall inspection and a pre-occupancy inspection.

After all of this, the occupancy permit issued by the municipality states quite clearly," The issuance of this permit does not imply complience with all Municipal bylaws or the Provincial Building Code"

Talk about CYA