Advice on soundproofing floors
January 6, 2010 7:15 AM   Subscribe

What is the best way of sound-proofing a wooden floor?

I'm helping renovate a house that has been gutted. The floor boards have been lifted and we want to make the floor as sound-proof as possible, within reason. We were thinking of putting hemp insulation (something like this) between the joists, and then some other fabric/rubber directly underneath the boards. I understand that the floor needs to be air-tight to reduce sound transmission but I wanted to know what the best type of fabric/rubber would be.

(Suggestions of products from the UK or Ireland are welcome as the house is in this location)
posted by a womble is an active kind of sloth to Home & Garden (7 answers total)
Lifted as in removed or lifted as in "pried up enough so I can slip something under them"? Most floor soundproofing assemblies usually involve a layer of Homasote (pdf link) between the finished floor and the subfloor, insulation in the floor cavity, and resilient channel supporting the wallboard on the ceiling underneath.
posted by electroboy at 7:42 AM on January 6, 2010

Check some references, because I am not sure you want 'air-tight' as you will end up having moisture problems.

I am doing the same at this point and am looking at blown cellulose for the R-value which doesn't help your noise problem. I am only commenting because of a moisture concern raised by your post.
posted by fluffycreature at 8:25 AM on January 6, 2010

Response by poster: To clarify, the floor boards are lifted completely and this is an internal floor/ceiling so moisture issues are not a concern.

Can you lay homasote on joists and put wooden boards over it?

Also, any thoughts on what the generic (or UK/Irish equivalent) of homasote is?
posted by a womble is an active kind of sloth at 8:54 AM on January 6, 2010

Best answer: No, homasote isn't structural. It'd need to be (from top to bottom)

Finished floor
Plywood or Floorboards

Not sure what the UK equivalent would be. Fiberboard or something similar? Homasote is basically a wood pulp board that has some insulating (both sound and thermal) properties, but not much strength. It's lower density than the fiberboard that say, Ikea makes furniture from, sort of papery.

Also keep in mind that unless you secure your floorboards really well, they may creak and squeak once they begin to loosen a little.
posted by electroboy at 9:12 AM on January 6, 2010

The best would be a layer of concrete to add mass to block foot steps.
  1. Insulate the joist spaces with either fiberglass or cellulose.
  2. Lay your plywood sub floor. Gluing the subfloor down will go a long way to prevent squeaks and strengthens the floor; they make special adhesives for this purpose in caulking tubes.
  3. Laydown your plastic sheeting to provide an air barrier and provide a moisture barrier for the uncured concrete.
  4. Pour in at least a 1.5 inches of concrete finishing to level or smooth if you want exposed concrete floors. Special light weight mixtures called gypcrete are available for this purpose depending on the strength available from your joists.
    • If the house has a boiler you can embed pex tubes in the concrete to heat your floor before pouring. The tubes can be fastened directly to your sub floor.
  5. For final finish you can:
    • Float hardwood or laminate.
    • Paint or stain the possibly stamped concrete.
    • Linoleum or vinyl.
    • Carpet (avoid if you did the pex tubes).
If the concrete is going to be too much work or money you can use regular sand to add mass to the floor. Change step 4 to: Strap the floor with 2X4s laid 16" on centre and running across the joists. Add pex in the spaces if desired then pour in sand. Affix another layer of plywood.
posted by Mitheral at 11:40 AM on January 6, 2010

The best would be a layer of concrete to add mass to block foot steps.

Yeah, don't do that. You need to know whether your floor can handle the additional load before you start adding 15 lbs per sq ft or so to the weight of your floor. If you really want to do that, talk to a structural engineer.
posted by electroboy at 12:25 PM on January 6, 2010

Best answer: Homasote would be similar to Celotex in the UK. It is a fibrous, lightweight panel board that would have to be sandwiched between your sub-floor and the finished flooring. It would not be very effective if the finish floor is nailed through to the subfloor, since the sound conduction through the nails will negate the much of the insulation. Gluing would be better if feasible for your flooring type.

Resilient channel on the ceiling side will greatly improve sound deadening as shown in electroboy's first link on homasote. The key is proper installation. For the ceiling below the floor you would use RC-2 resilient channel which should be available from your drywall supplier. Make sure you use RC-2 type channel and not standard drywall furring channel. RC-2 has a special expanded metal construction that makes it resilient to deaden the sound.

You fasten the channel to the bottom of the floor joists with screws on the two flanges. The channel runs perpendicular to the joists. The drywall is screwed into the channel making sure that no screws go through the drywall into the joists, which would destroy the isolation. The drywall floats on the channel preventing sound from transmitting through the joists to the ceiling below. Resilient channel is often used in multi-family construction in the U.S. which must meet certain acoustic requirements between living units.
posted by JackFlash at 12:59 PM on January 6, 2010

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