Condo kitchen floor with 2×10 joists, 16″ OC, spanning 15′, OSB on top glued and screwed. Owner wants me to stiffen it up.
Luckally the basement under that area is open ceiling and mostly unobstructed, however there is a gas line and a cold air return which will prevent sistering 15 foot material without a butt joint.
Would like to hear your thoughts and ideas.
Listeners write in about running a profitable contracting business and ask questions about patching drywall, adding air barriers, and fixing a patio poured against the house.
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.
Start Free Trial NowGet instant access to the latest developments in green building, research, and reports from the field.
Start Free Trial Now
Replies
Basement have the headroom for a midspan girder?
J. D. Reynolds
Home Improvements
Yes, there is plenty of headroom. Will posts be necessary to support the ends of the midspan girder? Or is there a Simpson tie that could be used to attach to each of the joists? Not sure they would want the posts but could ask.
How about recessing some LVL beams? I removed a load-bearing wall from my basement that had two stories above it. Built the temp walls to transfer the load. Cut the joists where I wanted to install the LVLs. Installed three LVLs (1-3/4" by 11-7/8). Nailed the three LVLs together (love my framing nailer) and nailed (with hammer) the joist hangers (special ordered hangers). Then nailed the existing joists to the new hangers and removed the temp walls. Oh, I did provide additional support at the ends of the LVL beams. :) No bounce.
Midspan girder would be best. If you can't add more supports, or lose much headroom, plywood on the underside can help a lot. It makes the joists more like I beams, providing more material where the stress is highest. It also keeps the joists from deflecting side to side.
How about blocking between joists? Done properly this transfers the load between joists, reducing overall deflection.
happy?
bounce over the whole floor or just particular areas? could either use plywood as mentioned, 2x4 flat on existing (i beam effect), or blocking between joists at 1/3 or 1/4 distance separation (not saying that well) to tie joists together - might also want to look at what's on the floor - lot of heavy furniture?
good luck
How much area would you need to sheet with ply to make it effective? Would one row of 4x8 (4' wide) down mid-span help alot, or would you need to sheet more area?
Any portion that you do should be helpful, but the more area the better.
When a floor bounces, the surface is deflecting which causes the bottom of the joint to spread apart.
This bouncing affect the furniture more on the wall that is parraell to the joist due to the spreading of the bottom of the members.
Attaching plywood across the joist with glue, screws and nails, along with jacking up the center of the floor will make it stronger and stiffer.
With the plywood underneath, it incorporates all the theories that go into boxbeams, trust-joists and post-tension construction.
With the type of bouncing you describe, simple X blocking between joists can be quite effective, especially near the wall.
If ignorance is bliss why aren't more people
happy?
I think that will work. As mentioned, the blocking was lacking, many removed by mechanical I think.
I'am a fan of solid blocking. It drives the trade subs nuts but I've never had a springy floor. I like 6' centers. In a retrofit situation, the bays with plumbing or mechanicals need some extra attention but you can usually find a way to get everything locked. I'd jack the floor before blocking to get it as close as can be to where it belongs.I fid x bracing has too much flex and it pops loose too easily.Just too many builders doing 360 floors and thinking that the minimum is enough, it just take a few extra bucks and hours to geta 720+A plywood skin hides all the 'works' and within a year something is always changed that requires pulling/ cutting sheets is the chase down of whatever is being changed/repaired
Yep, do what Dan and Pete say, even double blocking or x braces. Own house is also 15 ft. 2x10 16 OC (but with 1" plywood over, #1 DF or better) and has no noticeable deflection or bouncing.
Used 2 (TWO) sets of metal X bracing between joists at 5 ft spacings. (PS, the x bracing lets you store LOTS of 10 ft conduit, pipe, and of even longer molding pieces between the joists.
always thought x-bracing was for holding the joists vertical/aligned more than transferring load - also, isn't it difficult to nail the upper end of the X with the floor in the way?
One reason why many carps do such a lousy job of installing X bracing is that they think it's only to hold the joists vertical until the sheathing is on. In fact, an important reason for having the bracing is to tie adjacent joists together to reduce "bounce".True, it's harder to put X bracing in place once the flooring is on (and harder still once the ceiling is on :) ), but you can probably manage fairly well with Piffin screws or maybe a power nailer that isn't too huge. Worst case you could use some sort of Simpson bracket.IMO, wood X bracing is better than most metal schemes (which really are more cosmetic than effective). Maybe a piece of angle iron lagged to the joists would be better than wood, but the adjustable tin things that are jammed into place are next to worthless in terms of transferring loads.
If ignorance is bliss why aren't more people
happy?