Ceiling noise insulation against footfalls (without lowering ceiling)

January 31, 2018 11:17 AM

Looking to insulate the ceiling of a basement apartnment for sound. I currently have half of it open for a rewiring project. Can't really lower the ceiling appreciably because 1) it's already at a minimum height and 2) I don't want to rip out the other half of the sheetrock, so iso clips, or Green Glue plus another layer of sheetrock won't work. Ideas inside....

Also, cheap is a very good thing. Possibilities suggested by the Internet:

1) 2 layers of sheetrock with green glue in between, and GG above top sheet up against the subfloor, in between the joists. (hard against joists? With gap filled by acoustic sealant?)

2) (leftover) rigid foam insulation sheets in between joists

3) (leftover) fiberglass batting in between joists

4) Green Glue on bottom of joists between them and the ceiling sheetrock (will it adhere, or fall back on my face?)

5) maybe some thin acoustic mat designed for cars on bottom of joists instead of GG? (eg DynaMat, Rock Mat, etc.)

6) Something better you know about?

Thanks!

posted by msalt to Home & Garden (8 answers total)

The best way to reduce sound transmission through walls and floors is to start in the space where the sound is generated. In this case, carpeting on the floor above would do that. To go beyond that, either above or below the floor what you want is an air space with as little bridging as possible. This can be done, for example, by installing a floating acoustic neoprene "hockeypuck" floor. If installing above the floor is not possible, you should emulate it as closely as possible below the ceiling. Not between the joists, because then the joists will still transmit most of the sound. So for example, your No. 1 idea of two layers of sheetrock would work, but only if they were attached below the ceiling, with as much space between the two layers and as little connection between them as possible. Or Green Glue between them, and between the top sheetrock layer and the joists. (I'd still use some screws.) With fiberglas or polyurethane insulation between the joists.
posted by beagle at 1:04 PM on January 31, 2018 [2 favorites]

Also it is important to have an air barrier to reduce the transmission of high frequency sounds. This can be done just with gyproc if you seal penetrations properly (with acoustical sealant) but it is often easier to use a plastic vapour barrier as a primary barrier. This can also involve replacing any electrical box in the ceiling with vapour barrier style boxes or boots and enclosing any can lights with plywood
posted by Mitheral at 5:18 PM on January 31, 2018 [1 favorite]

Footfalls are an impact sound as opposed to a transmitted sound. That means that most of the energy is coming through the studs. Any system that mostly works between the studs and uses fasteners to affix the drywall ceiling back to them will have minimal effect. Dense insulation in the cavities may reduce ambient sound transmission and wouldn’t hurt. If iso-clips are out of the question then your other good solutions are changes to the floor or subfloor above.
posted by meinvt at 7:53 PM on January 31, 2018 [1 favorite]

Response by poster: Thanks, all. Any thoughts on DynaMat or some similar thin, sound-deadening layer on the bottom of the joists and above the ceiling sheetrock? That seems like the best alternative to Green Glue on the bottom of the joists. (and easier to install)
posted by msalt at 11:31 PM on January 31, 2018

If you are committed to putting something between joists and gyp board than you’ll get the best performance out of isolation clips. Any solution that still requires direct fastening of the board to joists will have minimal effect on impact noise.
posted by q*ben at 6:47 AM on February 1, 2018 [1 favorite]

Response by poster: Good point, thanks. Yeah, iso clips won't work because of the height.

Something squishy betweet the joists and ceiling sheetrock would at least reduce the footfall vibration to the area right around the screws, would it? Instead of all along the connection?
posted by msalt at 4:58 PM on February 1, 2018

If you have a little bit of room I think a second best would be the u-shaped rubber isolators, that would provide some protection from impact. Fill or mass damping would handle higher frequencies. I’ve never used them but they could provide some improvement.

Edit- colleague suggested these:
posted by q*ben at 7:50 PM on February 1, 2018 [2 favorites]

Response by poster: Interesting!! So if I'm seeing this right, you affix these to the sides of the joists, up in the rafters, instead of off the bottom of the joists, so that your furring channel or whatever can hang from inside the joists to just barely below them?

That's a great idea.
posted by msalt at 12:39 PM on February 2, 2018