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Attic floor a little shaky

John Z's Avatar

Join Date: Apr 2006
Posts: 9

02-09-07, 12:56 PM   #1  
Attic floor a little shaky

I'm remodeling my attic and one section of the floor is a little shaky. When I throw my weight on it, i can get about .5-1" of play up and down. (I am 6'4" 250lbs., so I can make most floors shake if I want, but this one shakes a lot more than most) I want to know what options I have in strengthening it. I am assuming that the joists may be a bit loose or something along those lines. It is not shaking enough to really worry, but I'd rather have it not happen.

Directly underneath it there is a newly finished kitchen, with wires running through the ceiling joists.

Any help or suggestions would be appreciated.


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Kobuchi's Avatar

Join Date: Aug 2004
Posts: 1,210

02-09-07, 01:26 PM   #2  
Most likely the joists are undersized. This attic - did it begin life as an unfinished attic, or as a *floor*? There's a big difference. Can you see the joists? If not, now's the time to cut in and check.

If the springy area is near the centerline of the house, a load-bearing wall (below) may have been thoughtlessly removed.

If you do need to strengthen the floor without raising the height, steel is probably the best bet and not so costly or difficult as you might guess.

Wayne Mitchell's Avatar

Join Date: Dec 2005
Posts: 3,188

02-10-07, 10:05 AM   #3  
John - attic joists are often designed with a different load requirement than a living space. Your ceiling joists (attic floor) are probably a bit undersized, typically 10PSF compared to 30 PSF for a living space floor.

You may not be able to get a permit for your project without doing something to strengthen the floor.

An inch of deflection when you stand on it is pretty springy. Add a couch, your 250 lbs and a couple of other big guys and you get the picture.

I suggest you measure the span, spacing and size of your joists. From there you can find span tables on the internet to determine what they should be.

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