Joist Sistering

[jseklund]

Ok, I'm trying to keep this simple and breif. As many of you know already, I have been renovating a hosue that I bought. A week ago, a friend of mine stepped on the floor in the dining area/kitchen and I saw it sink about 1/2". This totally shocked me because I had never seen it over the last 6 weeks, and it looked like a trampoline. I was going to put tile in the kitchen that night, which obviously wouldn't work on a bouncing floor, so I paid to have two guys just sister the joists below and sturdy the flooring. The run under that section was about 12' long. They used an 8' and a 4' run on each joists, staggering the joints, gluing, screwing with timberline screws, and nailing. The floor has lost maybe 90% of it's bounce and was sturdy enough to put the tile on (I guess all floors have SOME deflection). It's good now.

I was going to do the other side of the basement myself (since I wasn't putting tile in over that space it wasn't a priority and I will have time later). However, I had someone who saw the work the guys did on the sistering tell me that you shouldn't cut the boards and that they have little structural value because they did that. He said they should be 12' runs period.

Is this true? Obviously a long run would be prefered, but getting them on the sills would be a TON more work then. What is your opinion?

Thanks, as always, for the input/help.

[LCHIEN]

If I understand, they sistered the joists by screwing them into the sides of the existing joists? And that they used 8' + 4' pieces instead of a 12' which would have spanned the length?

it sure seems to me that single-piece joists would be 10X stronger. Particularly if the existing joists were weak to begin with.

[jseklund]

You are reading correctly, and I think you are correct...I don't know what to do, since it costs me a good amount of money to have it done and it was done wrong I think....especially since it was done wrong and I now have tile above it. I'm afraid that trying to correct the situation may break the tile....

[Uncle Cracker]

You could put 12-foot joists on the opposite side of the existing ones, without removing the 8's and 4's. If you don't jack up the floor in the process, you should not cause damage to the tile. Use screws to keep the pounding and vibration to a minimum. Using an 8 and a 4 on each was not good.

[Greg in Maryland]

What is your opinion?

What I know about this could hardly fill a thimble, but of course it does not stop me from having an opinion ....

I would suggest you contact your local permitting office and ask to speak to a home inspector or someone else in the know about code and common construction practice. Take pictures and describe the original problem and solution. See what they have to say. You pay taxes and that is what they are there for.

If, as you suspect this is substandard work, go back to the contractor and bang them over the head with the facts and request that the work be redone correctly. Unfortunately, there is a great likely hood that the original contractor won't do a thing, but if you don't ask you definitely won't get them to resolve it.

Also you can file a complaint with the contractor's licensing entity and Better Business Bureau.

Good luck!

Greg

[jking]

When you say they staggered the joints, do you mean from one joist to the next? In other words on one joist the put 8'+4' and then on the next joist they put 4'+8'? What size joists do you have & what spacing? I'm a bit surprised your existing joists would deflect 1/2" over a 12' span.

Yes, a 12' sistered joist would certainly be better. It would also be the common way to strengthen the joists. You do get some value from the 8'+4', however. You've received some good advice above about how to remedy.

[Hellrazor]

Can you post a picture of the work?


If I am reading this right, they did a big FUBAR. The joists need to be the same length as the original and NAILED or lag bolted together. Unless they used structural rated screws. Normal screws are not allowed for framing applications since they have poor shear strength.

Other questions.. what size joists did they use? What is the spacing 16" or 24" OC? What kind of decking is on the floor and what is the thickness?

[pecker]

Well, I'll be the contrarian. Whether it meets any type of code, I have no idea. But the concept of scabbing a bunch of shorter pieces together to form a longer beam is not unheard of. The fact that 90% of the bounce is gone tells you it had a great improvement. And how could it be any weaker than what was there already?

If the span had been huge, like 24ft or more, an engineered beam made that way would probably have been used originally.

[Hellrazor]

If the original joist failed, the scabbed joist would fail instantly.. therefore its not aceptable.

Here is the litmus test for this:

Show me a picture of a 10' garage door with a scabbed header that is weight bearing

[jseklund]

Thanks for all of the replies.

Jking- that is what I meant by staggered joints- 8+4 length on one joist, 4+8 on the next.

HellRazor- They used some heavy duty Timberland screws. The people who brought up the issue with the cuts, told me those screws were a good idea actually. I beleive they nailed it too. I know they glued it.

Pecker- Thanks for the optimism, it is much appreciated. I kind of thought the same thing- but my concern is that over time the bounce will come back, and if an inspector sees it....he may take notice.

The joists are 2X8 (Everyone, including the original workers, agrees it should be 2X10), 16" on center (At least in theory- I did some bridging myself in another area to support the ends of some plywood, and they were give or take 3/4"...not sure if that's normal in construction, but I don't woodwork like that). The flooring above is 1/2" plywood (hate that crap).

[billwmeyer]

Deflection

I have to agree with Pecker. The object was to minimize the deflection of the floor. This was done. It will strengthen the existing joints. I agree that full length joists would have been better, and lag bolts would be stronger, but reinforcing with glue and screws works almost as well. If the deflection is gone, you got what you wanted.

Bill

[Pappy]

Assuming that the repair is up to code, or that the contractor won't fix it if it isn't, you might go in and scab another 4-6' piece across the joints they created. This would reinforce the joint if the original joist should fail and should further minimize the deflection.

[jseklund]

Again, thank you all for the replies. I think what I am going to do is actually run another 12' section along side the cut boards- kind of sandwiching in the bad boards between two joists. I hate doing this because it's overkill, but seems like the most reasonable way to be certain things are good under there and not raise any code issue. It should be solid as a rock then, huh?

The wood will cost me about $150, and $50 for screws, glue, etc. So, it's a mistake that I can fix for $200 and probably 6 hours of my time. I know time is money, but I guess it could be worse.

[cgallery]

God I hate contractors. Always doing things the easy way.

[LarryG]

I've been watching this thread develop, but have withheld comment since structural design is not really within my area of building design expertise (to the extent that I have any). But curiosity finally got the best of me and I just called our primary structural consultant and asked him about this.

He response: for a simple bouncy floor, with no requirement to double to load carrying capacity of the joists, what the contractor did is perfectly fine. Indeed, he said that putting the splices at the third points and staggering them from one joist to the next is good practice. (A bad solution would have been to put all the splices right in the middle.) He said that the fact the splices are staggered shows that the contractor was thinking.

Another solution, assuming the bearing ends of the joists were in good condition, would have been to sister on a single piece that was as long as practical -- let's say 11'-4", centered on the existing span, with a 4" allowance for bearing (on the stated 12' span) at each end. IOW, everything would be sistered continuously except for the 4" at each end, which would not be sistered at all.This, he said, would have come pretty close to doubling the load-carrying capacity of the floor -- the only limitation being that the joist ends would have to be in good shape, with no indications of an impending failure in shear. (If the joists were notched at the ends, and the wood from the notch point down was splitting away from that above, that would be a shear failure, and this would not be a good solution.)

Another good option, theoretically better than the 4'/8' combo, would have been a 1' piece at one end, a 10' piece in the middle, and another 1' piece at the other end. But, again, since the objective was merely to eliminate bounce rather than to increase the live load capacity of the floor, the solution with the splice at third points is just fine.

All in all, pecker's reply come closest to saying what our engineer told me. That the bounce is mostly gone proves that the solution worked. The floor was in no danger of failing; it was just a little bouncy. It's now better than it was. The desired outcome was achieved.

BTW, I did not mention to him that you were considering adding a full length piece to the other sides of the joists, but from everything he told me ... I wouldn't bother. I'd be glad to ask him, if you like.