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.