Joists resting on foundation top...

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Old 08-23-06, 06:24 AM
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Joists resting on foundation top...

House built 1865, balloon frame. It's a small, simple house, mortared stone foundation in good shape, roughly 25'x18', a girder in the middle with approx 5.5"x5.5" joist mortised into the girder and resting on the foundation at the other end. They alternate milled and roundwood, and are somewhat irregularly and widely spaced (2' more or less)- the roundwood joists are rotted, the girder and others have no rot but are sagging some, shored up with a couple 4x4"s and jack posts. I've pulled up the floor/subfloor and figure I may as well just replace the joists and girder, but I'm wondering how to deal with the ends that rest on the foundation. The clearance between the top of the foundation and where the bottom of the subfloor should be is only about 5.5"- not much clearance. 12" or more from the inner side of the foundation to the rim joist, so plenty of clearance in that direction. Seems like there isn't room for anything other than to have the joists rest on the foundation top, as the originals do, and even then if I use 2x8s I'll have to notch them to fit. Should I use pressure treated lumber for the joists as they'll be in contact with stone/mortar? I was thinking a doubled up 2x10 for the girder replacement- the ends will also have to be notched to rest over the foundation, but I'll put a post at each end and and one in the middle. Ideas, suggestions?
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Old 08-23-06, 10:41 PM
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You seem to have some of the same issues I have in the post right below yours. Mine is also balloon framed but made in between the wars.

It seems like there might be a lot more seekers than dispensers of wisdom around here of late.

With your question one might need to know the span for your joists before you can start planning lumber sizes, but I'm not sure how to read a span table when it comes to notching.

Are you spanning 9 feet or 12 feet? I assume we talking 40 psf live load. If something needed to be in contact with foundation PT wood would be called for. However, I would expect some serious shrinkage unless it had dried out a thoroughly. I would want to find out what grade the PT wood to know what it can span to. You might consider using 16" or 12" OC instead of 24" You could span almost 11 feet with 2x6 if you use 12" OC.
or about 11 feet with 2x8 if you use 24" OC

I guess just raising the whole house up a few inches to put some larger lumber doesn't make sense for various reasons.

good luck

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Old 08-24-06, 05:14 AM
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Thanks for the reply foursquare. I've also posted about the issue on some other sites and got no dispensation of wisdom as yet..

I plan to space 12" OC so maybe I can get away with 2x6, though I may have to reuse the jack stands and jacking beam that is currently in the middle of the span. Good points about the shrinkage issues an span ratings for pressure treated.

If I were embarking on this whole project earlier in the spring I probably would've jacked the whole thing up to accomodate larger lumber, put in a pressure treated sil (though the sil, except for on small spot, is in surprisingly good shape) and get it all done right. Don't have time for that before it starts to get cold now (and upstate NY gets COLD).
 
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