Regarding the Subfloor. Architectural Question
This morning I had an interesting conversation with an architect. He was telling me that in order to achieve the best sound insulation between floors, I should install the plywood subfloor floating, without nails or screws to the joists or beams. He was telling me that the nails are not needed and I could just…
This morning I had an interesting conversation with an architect. He was telling me that in order to achieve the best sound insulation between floors, I should install the plywood subfloor floating, without nails or screws to the joists or beams. He was telling me that the nails are not needed and I could just glue all the pieces of plywood together. He was telling me that each nail or screw will carry the sound between floors.
I know that is not common practice, but is he right? Is it crazy to install the plywood subfloor without screwing or nailing it to the joists or beams? Any opinions will be appreciated. The photographs are just for illustration. I’ve got them from the Internet, not related to our project.
The project is typical two families Brooklyn townhouse, 20×40 feet.
After my initial reaction, which was basically, WTF!!! and posting accordingly, I started thinking about the post (par for the course where I’m concerned, I usually don’t think that much before I post). I think what threw me off is the reference to a “floating floor” as well as talking about gluing the plywood together. In hindsight, I can’t believe that this is what’s being recommended, but instead the architect may be talking about a standard floor, but with no nails/screws, relying only on glue. So it’s not really a floating floor. I can’t believe anyone with their own stamp would recommend a floating sub-floor.
That being said, I’m not sure what code has to say about this, so that would be the first hurdle, and even if code allows, I’d be really nervous about relying strictly on glue. You’d have to use a solvent based glue, initially screw down the ply until the glue sets and then go back after the fact and unscrew the screws, hoping that the glue holds. If I were bidding on this job, I’d include a premium for the extra work, and I’d insist on a waiver for claims against the floor failing in the future.
I wonder if he means to install a plywood subfloor on the joists screwed and glued, then put the a plywood subfloor on top over the sound insulation matt…
He’s correct about nails, which also apply of course to screws. The mass of a floating floor acts like a Helmoltz resonator to burn out low frequencies as a mechanical energy. A nail through it short circuits this and gives that mechanical energy a path to the joists, much like holding a paper cup against a wall to hear what’s going on in the next room.
I used this approach on the walls for a couple of recording studios where we built conventional sheetrock walls and then applied Type X using only a flexible mastic and some temporary drywall screws (before I found extruded channels made for this). But I’d never do this with a floor for the reasons already mentioned. I’m also skeptical that it would even work once you started bringing in heavy furniture. Normally, you would float the entire floor, joists and all, on vibration absorbers.
Bear in mind that walls are built on studs which usually directly or indirectly attach to those same joists so unless you’re just looking to cut down on floor impact noise just doing the floor is only a partial answer anyway. The correct way of building an acoustically decoupled space is box-in-a-box.
I understand what your architect is talking about but as others have said, it is not recommended to “float” over the joists. I have installed two layers of T&G plywood glued and screwed to each other on top of an existing concrete slab. Between the slab and plywood (2 layer) a sound layer product is laid. so: structure, sound layer, 2 layers ply, finish floor (wood). in your case, you need a structural layer of plywood attached to the joists. on top of that you can do a floating floor. that is a lot of build up of material, dead load, expense and additional floor thickness. you should check those things. if that is not possible, lay a sound layer like QTesc (a rubberized sheet of various thicknesses)on top of the structural subfloor, then attach a layer of plywood and then your finished floor. a suggestion.
Second the glued and screwed. You have to watch your contractor to make sure they are actually doing it and being thorough. Makes a world of difference, especially down the road.
This brings another point to mind. One major function of a subfloor is to transfer loads horizontally through diaphragm action. When fastened to the joists, it ties the whole floor system together, thereby strengthening the whole assembly.
Above all else, I would strongly recommend that you do not eliminate this, for your building’s safety’s sake as well as your own.
If he is talking about the structural sub floor it’s hard to believe he has any engineering education,run away. If this is a sheathing above an old, existing sub floor then a laminated, two layer floor floated on a sound proofing membrane will work very well.
There is a soundproofing structural plywood similar to Quiet rock you could use.
You absolutely MUST fasten a structural sub floor to the joists. Construction adhesive adds strength an helps eliminates squeaks. Nails or screws are fine. Black sheetrock screw are not so good structurally as they are brittle and break easily. Go here to learn http://www.soundproofingcompany.com/solutions/soundproofing_ceilings/
I’ve always learned that the secret to really quiet floors is “glued-n-screwed” subfloor. It’s a lot of extra work, so it’s rarely done that way, but it really does prevent movement.
PS- there are flooring systems out there that are basically plywood, but they have T&G on all four sides, they have a stiffening sheet of metal sandwiched in between the plys, they come wrapped in plastic so the moisture content is well regulated. I might consider just gluing down one of those systems, but I certainly wouldn’t do it with off the shelf plywood.