Best soundproofing material for under floorboards

[Keith Halewood]

Hi,

What's the best, acceptable (building code etc) form of soundproofing material that can be placed/installed in the floor space between the ceiling below, joists and floorboards above?

Keith

[Ian Stirling]

Several layers of lead, spaced by foam. It depends what sort of noise you're trying to kill. Voices are much easier than loud music from a gigawatt subwoofer.

[andrewpreece]

An olde but goode ( allegedly ) method is to pour dry sand onto plywood strips supported just above the the lathe and plaster ( by battens nailed to the joists ), i.e. pour sand under the floorboards. It adds mass, which relects sound, and attenuates it too. It is necessary to be careful with the amount so that the structural integrity of the ceiling is not threatened - it is called sand pugging, my Collins DIY encyclopaedia says , and strictly speaking you are supposed to get a surveyor to look at the ceiling first ( they have to say that to cover themselves of course ). Just to repeat myself, the sand goes onto a plywood support structure ( covered in polythene sheeting, to make it sand-tight ), not the lathe and plaster which has little reliable strength.

Andy.

[Douglas]

What is the source of the sounds that you are trying to reduce? If it is impact noise, from footsteps, doors and drawers, then adding stuff between the joists inside the floor won't do much to help. These sounds are carried by the structure. Carpeting upstairs is often the most practical solution if this is the problem. Old plank flooring does not make a good acoustic seal. Sand is an excellent limp mass in a floor void until you have a leak or flood. Actually it remains an excellent limp mass and the water adds mass, but I have been told that a floor full of wet sand can lead to other problems. Chipboard and drywall are both pretty high up on the mass-per-unit-area scale, and if the space is available they are often much more cost effective than proprietary "acoustical" materials for the purpose of adding mass to a partition.