14′ span, 1-1/2″ x 7″ (true as measured) Weyerhauser #1 KD fir floor joists on 16″ or sometimes 12″ centers in a ‘factory’ kit house built mid-70’s. 5/8″ T&G flooring glued (sometimes) and 8d air-nailed (sometimes) under carpet.
To my sense the floor in the living room is a ‘teensy bit’ too bouncy when even the 26# Scottie gets moving across it.
I’m wondering if I can improve the stiffness much by gluing + screwing on uncut 1-1/2″ x 3-1/2″ SPF studs with the wide face towards the joist bottom edge?
These would run between the load-bearing ends at foundation (joists bear on 1/2″ 3-ply on top of poured concrete) and center wood beam, intention is to increase the chord depth of the joists for most of their effective length & thereby the stiffness with minimal impact on headroom in basement.
Other suggestions welcome.
Replies
Yes, that is sometimes done and will, in theory, help.
Some other options:
Add X bridging (or solid bridging) between adjacent joists. (This transfers part of the load to the adjacent joist and is particularly helpful when the sheathing is less than substantial.)
Apply plywood to the bottom of the joists, similar to what you propose, only with the piece spanning between two adjacent joists. Use "splices" where the 8-foot plywood sections meet. The disadvantage of this, of course, is that it blocks off the joist bays for utility access, but doing (roughly) every other bay can minimize this disadvantage.
"Sister" 2x8 pieces to the sides of the existing. This usually runs afoul of plumbing/wiring running at right angles to joists, however.
Thanks DanH...
I should have included info re: bridging already in place. I feel it's inadequate at best (crossed 1x3's or 4's) being kinda sparse and not well nailed whatsoever. Probably doesn't contribute much at all to load transfer.
Solid has always been my preference but where joists are close (10-1/2") It'd be kinda tedious to add. Still, maybe that PLUS a 2x4 on each joist bottom would be worth the work... staggered blocking wouldn't be too weird to secure using an impact driver & 3-1/2' construction screws.
Boxing in adjacent joists to me seems less worthwhile than adding a 2x4 flat-wise to enough joists in the central (traffic) part of the bouncy floor, but as I've never been confronted by a situation like this (I tend to overbuild) I'm going by gut instinct until I get opinions based on experience such as yours.
Once the wife decides it's time to rip out & replace the existing carpeting & pad it'll be my chance to secure the sheathing better to the joists. I've done that in the dining room and hall with 99.9% effective removal of squeaks & 'talk-back' from sheathing moving up and down on all those plain 8d clipped head nails the crew used.
With joists overspanned that badly I don't think adding stuff to them will help much. Just exactly how much difference it would make is just guesswork.
Adding a beam at mid span is the only sure-fire way to firm the floor up. But of course that messe up your basement.
Dog too big.
My two scotties are only 20# each and I do not have this problem.
Two Huh?
We've had as many as three at one time, what a circus that was! Seven in all since 1983, all but one came from Scottie Rescue.
Anyway, adding a new "wall" or even a beam mid-span would seriously compromise the basement space utilization, and as the affected side is my spouse's, I'm disinclined to go that route.
Besides, the floor has been in place and survived for some 35+ years. Doing anything radical isn't needed for health and safety improvement. My intent is to remove the jiggle-factor, nothing more.
hear that echo?
Nothing like making a redundent point. Happens alot when one makes a habit of shooting from the hip.
I would say your are being a JACKA**
but then that would be redundant since it happens nearly everyday on here.
gluing + screwing on uncut 1-1/2" x 3-1/2" SPF studs with the wide face towards the joist bottom edge?
DO IT!
Joist depflection is inversely proportional to the 4th power of the beam depth (moment of inertia) too lazy to calc the new 'I' right now but a 2x4 flat across the bottom will do betterthan a 2x2, which I can calc in head
- e.g 7.5^4/8.5^4 (counting subfloor in depth for the 7.5 but not for the 8.5 jus to be conservative) = 60% of the deflection for 2x2, probably more like only 1/2, or 'twice as stiff' in vernacular for 2x4. Strenght is only increased by about 40%.
NOTE; Be SURE to glue. Nailing ok if full glue line. The lateral shear (parallel to the beam length) at the ends of the 2x4 to 2x8 joist is highest at the ends, typically 16d at 2" spacing at the ends widening to 8 or 10 inch at the center.
Google 'built up beams' for the formula of lateral shear, but you will be OK with the glue.
If the 1-1/2" less head room is a problem, you can get about 40% reduction in bounce by screwing a 1-1/2" by 1/8" steel strap to the bottom of each joist, same type screw spacing as the nails (NOT piffin screws, 1/4" lags) - lots more work to install a steel strap
edited as original posted without line breaks!
Thanks!
junkhound wrote:DO IT!
I appreciate your affirming my 'bootstrap' engineering is sound, at least for the intended purpose here.
No worries on losing the 1-1/2" headroom; I'm the tallest in my small family group & would be well clear of the additions. Agree on the steel strap vs. 2x4 too, if for no other reasons than the expense, weight of steel, and need to drill so many holes....
Preferring an impact driver over(handing) a hammer at my age I'd opt for #9 or #10 3-1/2" SPAX construction screws (or similar) maybe angled inward a bit & staggered off the 2x4 centerlines at the ends, into pre-drilled pilot holes to avoid splitting anything. Regular yellow wood glue between wood faces ought to be sufficient over anything more $$$ like urethane or epoxy.