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Old 08-24-2010, 03:25 PM   #1
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Hi all,

I have gone through a number of thread over the internet and also had a conversation with a structural engineer and I think I just need a little help pointing me to the right direction...

Here's some background to my problem...

About 10 months ago, I had porcelain tiles and a new kitchen installed. At that time one area of the floor was higher than the rest so I had asked the contractor to left the subfloor up and sand down one of the joists a little bit, so that floor levelling would be much easier (yes I know, probably not a great idea at the time...). When the contractors put the subfloor back in, they accidently placed the subfloor parallel to the joists, not perpendicular. It was just over this one 8x4 area. I didn't know until later that this had happened...

about a month after the kitchen went in, I noticed that a number of tiles have actually cracked directly above one joist. The kitchen peninsula/island is sitting directly on top of this one joist. So thats when I found out the subfloor was not perpendicular to the joists. I figure that the kitchen island was too heavy to be supported by just one joist, and because the subfloor was parallel to the joist, the load wasn't being carried over to the other joists.

I called the contractor and he was being a prick about it, so temporarily, I put up some studs in the basement to jack the joist back up to level and prevent it from sagging again.

The joists are 2x8s over a 12' span. 16" o/c. Basement is unfinished so I have access to joists.

I spoke briefly to a structural engineer and he said I can strap the joists and add more blocking. Also to sister the weak joists with more members.

So 2 weekends ago, I sistered 3 2x6s to that weak joist. 2 of them on one side of the joist went all the way to the foundation walls, while the 3rd couldn't reach the ends due to existing plumbing (the 3rd piece was only 7 feet long). I applied PL premium and nailed with framing nails while having the joists clamped together. However, one of the joist was warped lengthwise, so the top of the last joist didn't meet flush with the other joist. I nailed it like crazy and hoped that this all would be strong enough. I did not add more blocking nor strap the joists as I ran out of time. Once the glue cured, I took down the studs that were holding up the joist.

Just yesterday I noticed that the joist sagged again.

So what I did lastnight was jacked it back up to level and added more blocking with 2x4s at every 16" in the areas where the subfloor was parallel to the joists. I hammered the 2x4's up so that its sitting right below the subfloor. I then also added some 2x4 blocking at the bottom of the joists between the joists, as I heard the bottom of the joists deflect more than the top.

I keep reading about the difference between stiffness and strength. I thought that by sistering the joists, I have added strength to that joist, but its still sagging. So my hope is that by transferring the load to other joists it would help. My fear is that by transferring to other joists, it will cause those joists to sag as well... So should I just try to sister all of the remaining joists? I remember doing a calculation online somewhere that 2x8 over 12 span, 16" o/c is not adequate for a porcelain tile install. Unfortunately I did this calculation this AFTER the tile install.

So I think I have the following options:

1.) Add strapping (1x4) and blocking. Would that make the floor any stronger enough to resist the sagging? I'm hoping this would spread the load to the other joists as currently, ALL the weight of the island is sitting on that re-enforced joist.

2.) Can I add a 2x4 parallel and below the joist (so that the cross section looks like an inverted T?). I suspect that this will add more tensile strength to the bottom of the joist and makes it a 2x10?

3.) Or a combination of 1 and 2, blocking adding the 2x4 and strapping, which would lower my ceiling by about 2.5 inches...

4.) Or just suck it up and sister every joist, then add blocking and strapping. When I sister the joists, can I use a smaller size, ie. 2x6 like I did with that other joist? I don't want to hammer in 2x8s just in case it shakes the floor too much and causes the tiles to crack.

I'm really hoping that option #1 is enough, maybe its wishful thinking?

Any help would be much appreciated.



I previously posted this in the flooring forum but didn't get any replies. I thought maybe this is better suited under the Construction forum. Any help would be much appreciated!

2 threads on same issue merged
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Old 08-26-2010, 06:24 AM   #2
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fitch beam ?
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Old 08-26-2010, 08:00 AM   #3
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I thinks its flitch.
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