Homeowner, finishing basement.
The first floor (basement ceiling) has the “china cabinet” shake type of vibration. Not really any noticeable bounce or sponginess. Just vibration – the high stiffness, low mass type.
The entire floor is over unfinished basement that I will be finishing. Ceiling will end up with drywall except for areas left unfinished for shop, storage and mechanical.
As a good amount of the basement will end up sheathed with drywall, I am wondering if it’s also worthwhile to strap the joists (underside) before drywall, or would drywall add enough diaphragm support to stiffen things up.
Joists are 11 7/8″ I-joists, 16″ OC, 20′ span on one side of beam, ~17′ on the other. Joists are Pinkwood PK i20. L/D 480 40/15 is 20’3″ per the span charts. So, we’re close to the limit.
Floors on both sides of the beam are subject to the vibration just about the same.
Options I’m considering:
1.) Just sheath it with drywall and hope for the best
2.) Strap the whole thing before drywall
3.) Web stiffening w/ USB rips
4.) blocking at mid-span where no HVAC ducts are
Some combination?
I am an engineer, just not the right kind for this – so if anybody wants to nerd out on technical details or numbers, I’m in.
Replies
Strapping will help. I talked to my lumber yard about this since I have I-joists in my own house and have the same problem They told me to strap the joists. I'm not sure how much it'll reduce the vibration since I haven't done it yet.
Your best bet is to find a structural engineer in your area and talk to them and have them look at the project. Definitely needs more than drywall.
Floor vibration refers to the oscillation or movement of flooring caused by dynamic loads like foot traffic or machinery. It’s essential to address as excessive vibration can impact structural integrity and occupant comfort.
I'm certain it's not dangerous. It's the common "china cabinet rattle" effect that Ijoist floors are prone to. Nothing excessive or concerning to the structural integrity.
This is a new build - we built in 2022. Had a good architect. I've checked the span tables, and no concerns.
I'd like to address it, but don't plan to involve a structural engineer.
As an experiment, you might try adding 1/2" X 8' plywood rips to both sides of a pair of I-Joists. Glue & screw them into the top & bottom chords.
Plywood not OSB. Good quality 5-ply B-C plywood.
First try with just the plywood centered at mid-span, then do the water glass test over those joists. Bet it'll help. LMK
Adequate I-Joist strength for the design load doesn't always translate into good performance under dynamic loads.
[structural engineer here]
Just my two cents but when the span table says 20”3” span and you’re going to be at 20’ size up one joist size or move them closer together.
Personally I’d just add more joists and go 8” on center instead of messing around with strapping etc.
One thought is a material called "Green Glue," intended as a sound control measure. It's a permanently viscous material applied between two layers of drywall. Install one layer on the ceiling or wall, then apply Green Glue to a second sheet and install it offset by a half sheet (staggered.)
To me, low mass, high stiffness says (potentially) acoustic frequencies. Green Glue is intended to provide shear damping between the 2 layers of drywall. Not cheap and kinda messy, but has a mildly good reputation.
https://acousticalsolutions.com/product/green-glue-noiseproofing-compound/?attribute_pa_sold-by=the-case&utm_source=google&utm_medium=cpc&utm_campaign=SmartShopping_-_Green_Glue_-_Google&utm_content=Green%20Glue&utm_term=&gad_source=1#video-modal
Also, check out SoundProof Cow-
https://www.soundproofcow.com/green-glue-vs-mass-loaded-vinyl/
OP doesn't have an issue with sound transmission but rather vibration - e.g. the 'walking across a stiff trampoline" effect.
OP has a problem described as "vibration – the high stiffness, low mass type." It's all vibration; what changes is frequency and amplitude. As the frequency gets higher, the perception and description go from "vibration" to "sound." (Relatively) high stiffness & (relatively) low mass tend to produce high frequencies.
OTOH, you haven't lived until you've walked across a freeway overpass (multi-ton mass, 100 foot span) and felt it "vibrate" at 1/2 Hz and 1/2" amplitude. It's weird...
I'm not saying Green Glue will solve the OP's problem, but it is intended for, and reasonably good at, solving comparable problems. I'm curious what the folks at Soundproof Cow would have to say about this problem.
Jumping back in after the holidays and a busy work month in January..
I've been fireblocking the perimeter walls at the joists with 3/4" plywood. I have enough leftover to try the "boxbeam" experiment, I'll let you know if there is any noticeable affect.
I'll echo that this is not a situation where sound dampening will help. Sound transmission is a different physics situation. Sonic energy energizes the surface materials, causes them to vibrate and transmit sound. Green glue absorbs that energy. What green glue would not be able to do is prevent directly-applied mechanical force (walking on the floor above) and prevent that form transmitting.
But, this idea brings me back to wondering if strapping is really the fix if I'm about to drywall the whole thing. If the problem is more low-mass/high
1.) Drywall adds a lot of mass
2.) Drywall has a pretty good performance in shear - I believe it can act as a shear panel
Just to clarify the situation, the strapping in my situation is fairly extensive. Something like 1500 sqft of ceiling. The cost is not totally trivial and the effort to install it seems tedious.
I happen to have leftover drywall sheets in the basement from the original build, and a manual drywall lift in the basement for ceiling panel install. I'm thinking about screwing a couple of sheets up as an experiment to see if that helps. The downside is that a couple of sheets can't mimic the overall mass of the full install, but it may indicate whether the strapping effect of drywall would do the trick w/o 1x3 strapping.
Thoughts?