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Old 03-07-2013, 08:46 PM   #1
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bouncy floor


I've read up on the typical ways to stiffen up a bouncy floor, but I can't seem to find a good idea for what I'm seeing at my house.

I'm not really sure what kind of subfloor I have going on in this house. Most of the house is very solid, but at one end the floor is noticeably bouncy when I walk across it. It doesn't help that my wife put a china cabinet right in the middle of the room that rattles anytime a person walks by.

Looking up from the basement I see planks laying across thick beams that are spread about 8 feet apart. The planks are 2x4 with tongue and groove. The wood beams sit on top of some large steel beams. Most of the house has plywood screwed or nailed to the planks below whatever floor is there.

What I don't see is the typical 2x joists that have been in every other house I've lived in.

The house was built in the early 60's and the basement was dug out some time after that.. The wood is all in great shape and the only place where I really notice any instability in the floor is at one far end of the house.

A picture looking up from the basement is attached. The 1x4's are just furring strips where the ceiling used to be attached.
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Old 03-07-2013, 08:59 PM   #2
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looks like you need to pull down the 1x's and add more floor joists into the floor system that goes onto the steel beams. that looks like a 4' or more span between joists . 2x's laid down flat like that do provide quite a lot of strength but will bounce if overspanned.

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Old 03-08-2013, 03:59 PM   #3
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If you've got 8 feet of span between beams with a sub floor made of 2x4s laying flat, you've got a trampoline. As near as I can tell, what you are calling a beam is actually serving as a floor joist. You need to add joists between the beams to bring the span down to at least 16". And that will depend on the distance between the steel beam and the next load bearing point, foundation wall, another steel beam or whatever. This is why we have building codes.
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Old 03-08-2013, 05:25 PM   #4
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Well, the whole house has a floor like that and it is pretty rock solid everywhere except one room at one end of the house. I measured and its actually 6 feet, not 8, between joists. Not that it's much of a difference if it should be 16".
I'll add some joists. It should be a fairly easy thing to do.

By the way. The wood beams/joists run the length of the house, which is about 70 feet. They have marks on them that make it look like they were supported by jack stands or some other column about every 7.5 feet, before the steel beams were added (at least a decade after the house was built). It's been standing for over 65 years without any other signs of structural problems, so I'm not overly concerned if it isn't up to current code.
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Old 03-08-2013, 06:25 PM   #5
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Actually, with a floor of "lumber sheathing" the on-center spacing of joists are much greater, 5' with 1-1/2" thick T&G as you have, first chart;http://publicecodes.cyberregs.com/ic...9_5_sec003.htm All depends on the thickness/species/grade of lumber. I've installed some similar at 48"o.c., but yours appear to be a very good quality/grade (small knots, etc.). They appear to be 2x6 ? or 2x4... and I've seen them 3" thick, are you sure they are only 1-1/2" thickness? Lumber of that grade (old growth) is scarce, today. Have you checked in that problem area for full bearing on the supporting beams/piers/girders? Adding joists is good, especially when adding tile or other weight to a "spongy" floor. Was that part of the future plan?

Gary
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Old 03-08-2013, 06:37 PM   #6
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No plans to add any weight. I'll take a closer look at how well supported the wood beams are at the end. There is some ductwork that makes it hard to see back there, but I'll need to get in there anyway to add some joists.

When checking for "full bearing" should I be looking for an obvious gap between the bottom of the beam and it's support, or will a problem likely be harder to see with the naked eye?

Last edited by dftc; 03-08-2013 at 07:04 PM.
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Old 03-08-2013, 07:26 PM   #7
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I have seen a lot of roof decks built like this. Single and double tongue and groove. What I dont understand about yours are what appear to be gaps where the tongue is not engaged with the groove of the adjacent plank. The wood looks like white pine or southern yellow pine. Were I you, I would simply add one double joist running perpendicular to the Steel Beam, centered between your other large joists. Use the largest joist that will fit, and roll it into place. You can chamfer opposite edges to make it easier to get in. Roll them in one at a time and nail together. Make sure you crown them before installing them. The ends should bear on side wall support fully if possible but at least 4 inches. Put a piece of sheet metal between masonry and wood. install 2 x 4 blocking between your new joist, and the existing joist to both sides and toe nail. That should firm up your floor a lot. If you can gun liquid nails on top of the new joists prior to rolling them in that would be good, and will help prevent squeeks
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Old 03-08-2013, 10:56 PM   #8
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Thanks! Sounds like a good plan.
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Old 03-09-2013, 12:11 AM   #9
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Quote:
Originally Posted by Gary in WA View Post
Actually, with a floor of "lumber sheathing" the on-center spacing of joists are much greater, 5' with 1-1/2" thick T&G as you have, first chart;http://publicecodes.cyberregs.com/ic...9_5_sec003.htm All depends on the thickness/species/grade of lumber. I've installed some similar at 48"o.c., but yours appear to be a very good quality/grade (small knots, etc.). They appear to be 2x6 ? or 2x4... and I've seen them 3" thick, are you sure they are only 1-1/2" thickness? Lumber of that grade (old growth) is scarce, today. Have you checked in that problem area for full bearing on the supporting beams/piers/girders? Adding joists is good, especially when adding tile or other weight to a "spongy" floor. Was that part of the future plan?

Gary
That might explain why my new upstairs floor is so firm....1 1/8" T&G plywood with 2x12 floor joists 12" OC
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Old 03-09-2013, 06:52 AM   #10
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That might explain why my new upstairs floor is so firm....1 1/8" T&G plywood with 2x12 floor joists 12" OC
You parking cars up there???
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Old 03-09-2013, 09:49 AM   #11
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You parking cars up there???
No....but our master bedroom is over the family room.........and....my wife is 16 years younger than me.......
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Old 03-10-2013, 06:28 AM   #12
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So, an update...

Like I said in an earlier post, there is some ducting that makes it hard to see the end of the wood beams and examine how solidly they are supported. I did some measuring and discovered that the area where the floor is bounciest is right above one of those beams. That didn't make much sense to me.
I pulled out my bore scope to take a look behind the duct and I discovered that the beam is resting on a thick wood post with what looks like a short piece of 2x6 laid flat on top. The 2x6 is broken under the beam. I can't tell if it rotten or what, but it definitely isn't providing the support it should. All the other wood back there looks good so I don't know why that one piece has failed, but hopefully it will be easy to replace.

I'll probably throw in the extra double joist while I'm at it just to be safe.

Lots of spider webs up in there. I think I'm gonna have to borrow a tyvek suit from work.
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Old 03-10-2013, 07:43 AM   #13
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No....but our master bedroom is over the family room.........and....my wife is 16 years younger than me.......
I guess we'd best leave that comment alone.
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Old 03-10-2013, 10:05 AM   #14
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Lots of spider webs up in there. I think I'm gonna have to borrow a tyvek suit from work.
during the summer, i open all the windows. and use a leaf blower to clear the webs out. then clean the floor.
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Old 04-02-2013, 06:22 PM   #15
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One last update.
After some inspection with a scope I suspected that the issue was caused by a failing support post at the end of one of the wood beams/joists. The support is a 6"x8"x16" block of wood that sits on a concrete base in the crawlspace that surrounds my basement.

I just went to the hardware store and bought a 15" jack post for about $30. It took me 3 minutes to install and my floor is rock solid again. I can run past the china cabinet without hearing a single rattle.

I plan to replace the old wood post as well. Supposedly this jack post is ok for a permanent installation, but it doesn't look very permanent to me.

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