Hello,
I have stumbled in from the Knot’s forum.. and had a bouncy floor question.
The house is 12 years old with 2 x 8 joists on 12 inch centers, the span is 13′ 6″, the sub floor is t&g 3/4 plywood (23/32) glued to the joists with 3/4 oak finish flooring running perpendicular to the joists. The floor has a lot more bounce that I like.. I know if the span is broken with a girder would help.. but it would seriously cut into my woodworking shop area below.. To add to the story, much of the plumbing runs perpendicular (gas lines and water feeds) under the joist bays.
What would be the best way to solve the bouncy floor, without selling the house?
Thanks for your help..
Replies
Have you read this thread?
http://forums.taunton.com/tp-breaktime/messages?msg=38570.1
Sistering the joists with 2X10s might be your best bet if you don't want another beam.
I want to eliminate human suffering - namely mine.
With joist bays open at the bottom, the bottom edges of the joists are free to deflect a tiny amount perpendicular to the joists, allowing them to twist. This twisting of the joists is the mechanism behind the bounce.
Perpendicular blocking between the joists restrains the bottom edges and stiffens the floor. For a shop area where appearance isn't such a big deal, run a couple 2x4's perpendicular to the joists and see if that helps. I'd divide the span into thirds and try to get long enough 2x's to not have splices, if possible. Face nail two 16d thru the 2x4's into each joist. That's an easy enough fix to be worth a try. If it doesn't help, come back and tell us....
-- J.S.
John,
Thanks, sounds simple enough, I will give it a try..
For SPF lumber the span tables say 13'-9" for a 30# live load (this is the loading for sleeping rooms and attics) and a 12'-6" span for a 40# live load (kitchen, living, dining, etc.) You are either at or over the span table limits.
The lateral bracing suggested may help, but the tables assume that the joists have some bridging or other support to prevent this type of twisting. So, IMHO your problem will probably not change notiecably by adding the bracing, especially if you have bridging in place now.
Read this thread by one of our "guru"s
<PFloor Vibration
SamT
Woodtick,
The bridging or blocking is really lame, looks like 1 X3 strapping, half of which are either missing from the mechanicals installation or never were. I had toyed with the idea of using solid blocking, but have read in FHB that blocking between the joists causes squeaks...
I think my brain deceived me as I really believe the span is 12' 6" not 13' 6" as reported.. Because I remember looking up the information in a span chart and noting that the floor is at the hairy edge of the chart (the area is kitchen, family room), assuming all the joists are #1 SPF (don't look it to me).
Every owner in the development complains about a bouncy floor in the section of the house that has this large clear space in the basement..