Correcting sagging floor with house on beams

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Old 08-06-10, 06:35 AM
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Correcting sagging floor with house on beams

Okay, I've been all over asking questions since we started planning to buy a particular house, and now we're committed and I've got a lot of my plans made. What I still need to hash out the details of is how I'm going to shore up the floor joists.

So here's what I know about the house. It was built in 1917 and it's a 1-1/2 floor bungalow built on piers in southeastern Michigan. The overall outside dimensions of the house are 22' x 39'. The joists run in the 22' direction. I don't know the joist spacing for certain, but if it's any indication the roof rafters are 24" spacing (and 2x4's!!!) I don't know the joist size either. And I don't know how the beams and piers are currently laid out, but what I do know is that our inspector said that improperly constructed piers from various things like wood posts and/or stacks of concrete blocks have been added in ill-advised efforts to correct sagging floors, and the result is that the first floor has a lot of places that are crowning. The inspector advised that part of what I need to do is remove the improper supports.

Long term, like in 3 or 4 years, I plan on having a foundation poured around the perimeter, which I'd most likely plan to build a knee wall on top of to which the existing structure will attach. At any rate, what I do now I want to plan on being sufficient to last until then, and to be built in a manner that it won't interfere with that work when it's done (i.e. provide clearance for the excavation).

Oh yeah, more about the crawlspace. It's about 3' tall, dirt floor, no insulation on the perimeter or in the floor joists, no vapor barrier. All of which I plan on resolving, but I haven't worked out the details. What I know is it NEEDS to be conditioned because the heater is in the crawlspace as is the humidifier, which would likely freeze without the crawlspace being conditioned. I'd love to move the heater to the utility room, but that's beyond the scope of what I can do before winter this year.

I'm also going to add that what I'm describing here in terms of long-term and short term structural work I plan on consulting a structural engineer before starting, but I'd like to get soem idea if I'm on the right track and/or if there are any other suggestions.

So my short-term plan is that I'd like to put in 4 rows of 4x4 beams supported by either jacks or something else. I'm gathering that for each beam, I'd have to use 3 16' long pieces. So with 12 pieces of 16' 4x4, I'd have to come up with 36 jacks if I wanted to support each beam at the end and the middle. I'm having a hard time finding anything but telescoping jacks, which I know are supposed to be temporary... But isn't 4 years stretching the term temporary a bit? That and 36 X $25 adds up.

Could I maybe reduce the number of jacks I'd need by stacking 3 2x10 and staggering the joints to form continuous beams or something like that? If I put 4 jacks under each beam that'd be a 12' span roughly and I'd be down to 16 jacks.

And I'm assuming this is overkill, and I'm not hurting anything if I assume that I put in what I think is adequate and the existing supports can't be relied upon. 12"x12"x12" pads for each jack isn't going to affect my ability to put in the foundation wall later if I keep it far enough away, but how close can I get? I know I want the temporary supports to not be disturbed during the excavation, but I also know that the more the beam is cantilevered the more it's likely to be overloaded.
 
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Old 08-07-10, 09:32 AM
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Location: WA
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Invest in a Structural Engineer now. Disributed loads, point loads, footing sizes, post and beam sizes, fasteners, soil supporting capability, possible ground water drainage, and liability for your H.O. Insurance carrier are a few things that come to mind.

Be safe, Gary
 
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Old 08-07-10, 03:02 PM
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Like I said, I am already planning on that. We haven't even closed on the house yet, we're doing the closing as soon as possible once the title work is done which we're expecting to be next week. I've been in Mexico all of last week and being the weekend, the soonest I'd be able to contact a structural engineer is Monday, and I'd rather not spend any more money until after closing... besides which, I wouldn't be able to easily arrange for the structural engineer to visit the house until then anyway.

So, I also understand that while I'm committing to not use any answers anyone might give, I also understand that somebody else could read any answers and infer it as good advice for their situation. So if anyone could advise me if I'm on the right track but would rather not do so publicly, I'd appreciate a PM. All I'm looking for is information that is good enough to use for estimating my project budget, I won't be buying any materials until after I consult with a structural engineer for a final list of materials and plans.
 
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