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georgeh75 10-24-2008 11:40 PM

newb been lurking and reading have question
hello all!

My name is George, my fiance and I bought an older home built in the 50's. it used to have a wood burning stove that has a small bearing on my situation, in seeing what I can see the house has a perimeter foundation and then either every 8 or 10' there is a wall that runs from the front of the house to the back and the floor joist's rest on those. The problem I am having is that in the span of the floor joists from one wall to the next it is bowing due to the weight of an added concrete block flue that was for the wood stove. it is resting on top of the floor and not the ground below it, so I need to get under and jack it back up level. Then I read about wood retaining the bow that has been created over time "creep?". How would one go about jacking the center of a span and get the bow out, rienforce and set the center on peir footings? thanks in advance. George

Square Eye 10-25-2008 08:30 AM

The correct way to straighten out the bow is to sister new floor joists on the sides of the existing joists. The problem is, this creates a whole new set of problems, as in, squeaks, loose flooring, Problems at the joints in the existing floor...

What you might try, is to just jack the floor back up and see if it will straighten out as is. You might get a pleasant surprise. :)

Typically, We dig shallow, level bottom pier footings, Lay a 16" stepping stone in the hole, stack blocks on them to within 6" of the joists, lay a 4x6 across the top of the blocks. Then we put the jacks close to these piers and raise the floor by jacking the 4x6 against the floor, shimming the top of the piers as we go with 2" 4" 6" blocks and steel shims until we get level.

In your case though, A concrete block flue needs more. A deeper pier footing 32 to 36 inches deep, 30 to 36" square at the bottom, pour 12 to 16" of concrete and at least two 8" concrete blocks wide, 24" x 24" would be better. Mortared and built perfectly level and plumb. At the top, you need a barrier between the concrete and the wood. A piece of steel or aluminum would work there. Also you need to add wood on top of the pier so the joists are not bearing all of this load. You could add blocking between the joists. cut them to fit snug but not too tightly. You want to be able to position them easily. No banging and beating on the joists while they're under this load. Use screws to fasten the blocks. Make sure the blocks match the width of the joists so they will share the load. One at the back, one in center and one in front, in each joist space over your new pier. Sounds like overkill but structural failure would be overkill on your pocket!


As I sit here re-reading... The best thing you could possibly do right now would be to get a contractor or an engineer in there to assess the situation. A certified wood burner installer may be able to run steel triple wall pipe and you could do away with the blocks all together. There are options you need to consider and there are things there that I can't see that would change everything.

spaz2965 10-25-2008 09:31 AM

As square eye said there are different opinions that could solve the problem but without seeing it is difficult to tell you exactly what to do. I don't know without seeing it but you may be able to frame either walls under the sagging part or place a beam in under the center of the sagging joist running perpendicular to them and jack up the sagging part and put beam in, depending on the span that you are doing would clarify the size beam that is needed. Try and post pictures of what you have and what is underneath so that we may be able to help further on your situation. Getting an engineer in will get you on the right tract but from experience they really go over kill and can make things harder than what they are. Good Luck Hope some of this helps you out. There are some really intelligent people here willing to help you out.

georgeh75 10-25-2008 01:42 PM

thanks guys,

my dad lives down in california, he is an engineer down there, he says
'you have enough common sense to make it right and be sure to use math to figure out loading"... the problem is getting the bow out. Will jacking it up a 1/4 inch per hour over 4 or five hrs do the trick? thanks again guys, as soon as I get down there I will upload pics.. George

spaz2965 10-25-2008 03:01 PM

I would jack it up all at the same time I use a 5 ton hydraulic jack and use something good like 6x6 over your span and a 6x6 for your post now you may have to you a couple of jacks never had a problem as I have raised whole ends of walls this way. Depending on if anyone ever did some drywall repairs you may have some drywall cracks that you will have to fix. Also when done and header is installed if this is the route you go, make sure that you have enough bearing on both sides, and a solid footer or solid bearing to foundation. Hope that this is more help to you.


georgeh75 10-25-2008 03:29 PM

makes sense, I was going to use 2 10' 6x6 as you mention for the run and have the footings on 4' centers from the front to the back of the house. then marry 2x10 floor joist in for added support? gotta get some pics. thanks George

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