Sagging Floor Joists

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  #1  
Old 02-22-10, 09:52 AM
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Sagging Floor Joists

A little background information:

I bought my house about 4 yrs ago. The house was built in the early '80's without central heat & air. About 10 yrs before I purchased the house (14 or 15 yrs ago at this point), a previous owner added a central heat/AC system. The house is a single-story ranch over a crawl-space. When the previous owner added the central system, the furnace was installed hanging from the floor joists. Over time this has caused 4 joists to sag (~ 1" at the deepest point) between the outside wall and the columns running down the middle of the house. I'm trying to correct this situation. My question is the following:

What is the correct way to support the furnace in the crawl space so that I can begin straightening the floor joists?

I think I have a pretty good handle on how to slowly straighten the floor joists using a couple of jack-type braces and two 2x6's, but I'm not sure on how to best handle the weight of the furnace.

I've been given two different opinions by very capable individuals, but neither of them is really a builder. Here are those opinions:

Opinion 1: Dig a flat spot on the ground in the crawl space and build up a scafold of concrete block, topped with 2x4's or plywood to the bottom of the furnace and then remove the existing plywood frame connecting the furnace to the floor joists and let the furnace rest on the block scafold.

I don't love this option because I worry about the long-term integrity of the scafold-type support system. It just seems awfully amateur-ish, and like something that would cause a home inspector to through up a big red flag to any potential buyer.

Opinion 2: Install a couple of jack-type braces in the crawl space and slowly correct the sag in the floor. Once corrected, sandwich the existing joists with new floor joists and just leave the braces in place.

I don't love this option because it means that I'd be leaving the weight of the unit on the floor-joists. Also, it would involve leaving some support jacks/braces in the crawlspace, and I worry about the questions that would generate when I try to sell the house in 3 to 5 yrs. On the other hand, once the old floor joists were straightened and then reinforced with new joists, it would seem that I should be able to remove the braces with a reasonable level of confidence that the double-joists would be able to handle the weight.

What is the RIGHT way to fix this?
 
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  #2  
Old 02-22-10, 11:06 PM
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  #3  
Old 02-24-10, 06:41 PM
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I didn't notice nothing was there lost internet while editing. I would put the furnace on a temporary scaffold system. Then fix the sag in the joists by raising about 1/8" a day till level and then attach a sister joist to each one. Then I would build a support system for the joist Its basically a pillar support with a 4"x4" across the affected joists. See pic:

 
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Old 02-26-10, 05:18 AM
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Thanks

Thanks for the input. I have a quick follow-up question.

1/8" of an inch/day seems pretty fast to me. The room above the sag is a bathroom and I worry about upsetting the plumbing. I was planning on moving much slower, more like 1/8" twice a week.

I like the idea. Seems like a much more permanant solution.
 
  #5  
Old 02-26-10, 05:46 AM
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Hi JP. first, understand that a sister attached to a joist that has been forced back to straight, will rebound about half of it's memory. If you force them to be straight, they would have to stay there for years before they their memory is gone.

A furnace that is designed to hang from above, may not be able to be supported from below. Something you need to determine.

I don't see where you mention what your current joists are, 2x8 or 2x10 or what? But any common dimensional lumber, even with new sisters, will slowly sag. I would consider two engineered beams as large as you can get in there to take over the entire load. Engineered beams will resist sagging very well. The trick will be getting them into position.

Post a picture or two and we can be more specific. http://forum.doityourself.com/electr...your-post.html

Bud
 
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Old 02-26-10, 02:27 PM
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1/8" a day is the norm, it is actually a pretty small amount. But you can go slower if you feel it necessary.
 
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