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Old 11-29-2010, 06:51 AM   #1
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Floor Question


Hello,

My Dad and I built an addition on my house about five years ago. It is 24x24 with a full basement. My original house is ten years old (only five at the time) and was built with engineered floor joists. We used engineered joists on the addition, they cover the whole 24' span without support (we bought joists rated for this span on 16" on center"). There is one interior wall about 8' off of one end that runs perpendicular to the floor joists. I installed this wall "tight" as I was trying to reduce some of the movement in the floor (as it seemed to give when I jumped on it). This may have been a mistake.

So, within the last two weeks I've noticed an annoying noise when I walk into my bedroom closet in the addition, which is part of the interior wall I mentioned above. It sounds almost like a snap or loud creak. My wife thinks I'm paranoid, but I'm concerned this may be a symptom of a structural problem. I've examined the floor joists as the basement is unfinished and can find nothing out of place.

I'm considering putting up a 2x6 wall to shorten the span of the joists in the basement. Is this overreacting? Could I make things worse?

Any advice is appreciated, including what to look for in a serious problem.

Thanks!

Mike
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Old 11-29-2010, 07:06 AM   #2
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One other thing. The floor did get wet during construction due to a rainstorm. The floor is 3/4" t&g plywood. I wonder if the noise is being caused by warping of the top "ply"?
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Old 11-29-2010, 03:28 PM   #3
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You have a known problem


The floor joists are undersized for deflection. It is not a structural issue but floor will vibrate as you noticed during construction with the bouncing you experienced.

Generally wood construction tends to squeak because of excessive movement of wood members touching each other.

Adding the wall support in the basement as you mention will help.
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Old 11-29-2010, 03:39 PM   #4
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Originally Posted by ENGINEER10 View Post
The floor joists are undersized for deflection. It is not a structural issue but floor will vibrate as you noticed during construction with the bouncing you experienced.

Generally wood construction tends to squeak because of excessive movement of wood members touching each other.

Adding the wall support in the basement as you mention will help.
Thank you for the response. Do you see any down side to adding the wall? I was thinking of adding a 2x6 wall and anchoring it to the floor. It's a solid 4-5" pad with a gravel base.

The room is just a bedroom, nothing very heavy outside of some dressers.
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Old 11-29-2010, 04:02 PM   #5
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Did you use bracing when the joists were installed? Chances are, between the deflection of the joists and the shrinking of the wall you put in, and the nails from the wall plates, I'm not surprised you're getting some noises. It may only be seasonal but it's still annoying. I wouldn't build a wall underneath, as that will also expand and contract. I would put a beam with adjustable post jacks to support it. That way you can take up the slack or ease off as necessary
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Old 11-29-2010, 04:23 PM   #6
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Quote:
Originally Posted by mshoffman View Post
Hello,

My Dad and I built an addition on my house about five years ago. It is 24x24 with a full basement. My original house is ten years old (only five at the time) and was built with engineered floor joists. We used engineered joists on the addition, they cover the whole 24' span without support (we bought joists rated for this span on 16" on center"). There is one interior wall about 8' off of one end that runs perpendicular to the floor joists. I installed this wall "tight" as I was trying to reduce some of the movement in the floor (as it seemed to give when I jumped on it). This may have been a mistake.

So, within the last two weeks I've noticed an annoying noise when I walk into my bedroom closet in the addition, which is part of the interior wall I mentioned above. It sounds almost like a snap or loud creak. My wife thinks I'm paranoid, but I'm concerned this may be a symptom of a structural problem. I've examined the floor joists as the basement is unfinished and can find nothing out of place.

I'm considering putting up a 2x6 wall to shorten the span of the joists in the basement. Is this overreacting? Could I make things worse?

Any advice is appreciated, including what to look for in a serious problem.

Thanks!

Mike
What's the height of the I-joists?
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Old 11-29-2010, 06:17 PM   #7
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What's the height of the I-joists?
They are 12" and are made from what looks like 2x4s and particle board. The 2x4s are joined together in something like a saw-tooth joint.
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Old 11-29-2010, 06:21 PM   #8
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Originally Posted by mrgins View Post
Did you use bracing when the joists were installed? Chances are, between the deflection of the joists and the shrinking of the wall you put in, and the nails from the wall plates, I'm not surprised you're getting some noises. It may only be seasonal but it's still annoying. I wouldn't build a wall underneath, as that will also expand and contract. I would put a beam with adjustable post jacks to support it. That way you can take up the slack or ease off as necessary
I didn't install any bracing between the joists. Thanks for the idea about the beam. I've also read that bracing between the joists will help lessen the bounce or deflection. As opposed to cross bracing you can supposedly also just attach some 2x4s perpendicular at the bottom of the joists. Any thoughts on these ideas?

Thanks again.
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Old 11-29-2010, 08:02 PM   #9
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Originally Posted by mshoffman View Post
They are 12" and are made from what looks like 2x4s and particle board. The 2x4s are joined together in something like a saw-tooth joint.
The information about those joists spanning 24' was dead wrong. 12' I-joists cannot clear-span 24'.

How did this even pass inspections?
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Old 11-29-2010, 08:28 PM   #10
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Originally Posted by Joe Carola View Post
The information about those joists spanning 24' was dead wrong. 12' I-joists cannot clear-span 24'.

How did this even pass inspections?
I found the markings on them. 11 7/8" PRI-80. The span is actually only 22' 4" (24 x 24 is the outside dimensions).

This level of I-beam is rated for a simple span of 22' 8" by the APA (engineered wood association, http://www.apawood.org).
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Old 11-29-2010, 10:06 PM   #11
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A wall below will reduce deflection and therefore movement between wood members rubbing against each other. There is no downside once everything is positively connected with fasteners like nails and metal connectors.

A properly sized rigid beam will accomplish the same thing.

Blocking between joists will not do much to solve the problem you have but will help with lateral structural stability of joists, and increase their strength.

If the subfloor deck was not glued to joists during framing then nail popping emitting noise when joist deflects is possible too. This is fixed from above by adding screws into the subfloor to top flange of joist.

The joists you have are border line OK for the span.
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Old 11-30-2010, 07:08 AM   #12
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Originally Posted by ENGINEER10 View Post
A wall below will reduce deflection and therefore movement between wood members rubbing against each other. There is no downside once everything is positively connected with fasteners like nails and metal connectors.

A properly sized rigid beam will accomplish the same thing.

Blocking between joists will not do much to solve the problem you have but will help with lateral structural stability of joists, and increase their strength.

If the subfloor deck was not glued to joists during framing then nail popping emitting noise when joist deflects is possible too. This is fixed from above by adding screws into the subfloor to top flange of joist.

The joists you have are border line OK for the span.
Thanks for the feedback. A couple of questions:

1) All of the noise comes from within a foot or two of the interior wall I mentioned. This being the case, should I locate the supporting wall/beam directly under the 1st floor interior wall? Or should I try to put the supporting wall mid-span?

2) Any thoughts on beam sizing? Can I get away with a couple of 2x10s glued/screwed together?

3) You mention the joists are borderline OK. Do you think my problem is really more of an annoyance? Or should I be shoring-up my floor joists to solve/prevent a more severe structural problem?

Thanks again.
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Old 11-30-2010, 09:37 AM   #13
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Quote:
Originally Posted by mshoffman View Post
Thanks for the feedback. A couple of questions:

1) All of the noise comes from within a foot or two of the interior wall I mentioned. This being the case, should I locate the supporting wall/beam directly under the 1st floor interior wall? Or should I try to put the supporting wall mid-span?

2) Any thoughts on beam sizing? Can I get away with a couple of 2x10s glued/screwed together?

3) You mention the joists are borderline OK. Do you think my problem is really more of an annoyance? Or should I be shoring-up my floor joists to solve/prevent a more severe structural problem?

Thanks again.
Hey Mike,
A Couple of questions...
Having said that your outside dimensions are 24’x24’ and the actual span is 22’8”, my question is do you have a brick as your exterior siding?
Also do you have a blocking between I-J at the rim board section, and how did you nail your rim board?
Looking at I -joist it should be markings for OC spacing …what does it say?
What kind of sheathing did you use and is it glue and nail down?
Something else, I’ve seen I-joist being reinforced with ¾ plywood sheathing (panel closure) on one or two sides.
George
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Old 11-30-2010, 09:52 AM   #14
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Quote:
Originally Posted by ENGINEER10 View Post
A wall below will reduce deflection and therefore movement between wood members rubbing against each other. There is no downside once everything is positively connected with fasteners like nails and metal connectors.

A properly sized rigid beam will accomplish the same thing.

Blocking between joists will not do much to solve the problem you have but will help with lateral structural stability of joists, and increase their strength.

If the subfloor deck was not glued to joists during framing then nail popping emitting noise when joist deflects is possible too. This is fixed from above by adding screws into the subfloor to top flange of joist.

The joists you have are border line OK for the span.
I second this information, for what my vote is worth.
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Old 11-30-2010, 10:03 AM   #15
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Hey Mike,
A Couple of questions...
Having said that your outside dimensions are 24’x24’ and the actual span is 22’8”, my question is do you have a brick as your exterior siding?
Also do you have a blocking between I-J at the rim board section, and how did you nail your rim board?
Looking at I -joist it should be markings for OC spacing …what does it say?
What kind of sheathing did you use and is it glue and nail down?
Something else, I’ve seen I-joist being reinforced with ¾ plywood sheathing (panel closure) on one or two sides.
George
Hi George,

My exterior siding is vinyl.

I'm unfamiliar with blocking. Would this be a piece of wood between the I-joists at either end? The rim-board is attached with nails, and was supplied as part of the I-joist "kit".

The on-center spacing is supposed to be 16", which is how I installed it. Though I wish I would have bought a couple more joists and done 12" OC.

The floor is 3/4" tongue-grove plywood that is nailed and glued down to the joists.

Interesting. Would a panel closure involve attaching plywood vertically top to bottom down the length of each side of the joist?

Thanks!
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