If you live in a flat in a converted house with neighbours above, then you will know that sound insulation is an issue.
Floors of most old houses are divided by wooden floorboards, an empty joist void and a one inch thick lath and plaster ceiling. Even when carpeted airborne noise (voices, TV etc.) and impact noise (footsteps or thing being dropped) can be clearly heard below.
Some people don’t seem to care about this and some actually find hearing another human being above reassuring. For others, especially those with noisy neighbours, it is a constant source of irritation and distress.
Planning and Building Control
New subdivisions between dwellings need to comply with part E of building regulations and floors or walls have to be tested before regulation certificates are issued. The building regs are themselves a good source of information on how to sound proof buildings. If a certificate is require contact a sound test engineer before you start work and ask him what is required to get the premises up to test level.
Normally, boundaries between living spaces are tested but bathrooms, stairwells and kitchens are exempt, but check with the engineer who is going to do the testing.
Planners often want developers to stack rooms so that bedrooms are above and below bedrooms. This is a good idea but is not always feasible in converted houses.
Here I look at sound proofing options between floors in old houses, I will deal with sound proofing between walls in a separate blog.
Reduction of both airborne and impact noise between floors is best achieved by installing a false ceiling below the existing joist void.
It is best to leave lath and plaster ceilings in place. Pulling them down is hard work and messy. Besides the extra layer helps to dampen sound and provides fireproofing around the joist void. Below the lath and plaster build a sturdy timber frame. It is best if this is kept independent of the existing ceiling but on wide spans it may be necessary to tie the structure to the joists above.
Acoustic rock wool should be laid between or above this wooden fame and resilient bar screwed perpendicular to the battens. One thickness of 19mm sound block or plank insulation board is screwed to the bar then overlaid with standard plasterboard or extra block. This is a lot of heavy board so make sure that your stud work is strong enough.
Inset lights may violate your sound proofing and are best avoided. Personally I like up/down wall lights that shine light up so that it reflects down off a white ceiling. This leaves the ceiling as a clean uninterrupted plane.
If you are fitting inset lights, make some 200mm square boxes from bits of 18mm board and clad them with some sound block and place them over the fittings. These give the light breathing room and allow the insulation to be laid continuously over them.
False ceilings are unsuitable where there is insufficient headroom or when there are decorative cornices or ceiling mouldings that should be preserved. In this case the only option is to do something on the floor of the room above.
If there is sufficient headroom, a sub-floor can be installed over the existing floorboards. This is a timber frame that floats on specially made rubber cradles above the exiting floorboards. Acoustic rock wool is installed between the battens and the whole structure is boarded over.
Often in converted lofts there is not enough headroom for a sub-floor. If you can, lift the existing floorboards and pack acoustic rock wool between the joists. This is a lot of work and mess and may only be worth doing if you have to renew services anyway. Once floorboards are fixed securely back down you can overlay the floor with acoustic matting. Different mats are available but the decent ones tend to be very expensive.
My experience of simply laying acoustic matting under carpet is that little discernible improvement is achieved. A more thorough approach is to overboard the matting with chipboard flooring then fit skirting boards which should be sealed on top and bottom edges with acoustic mastic.
A cheaper, solution is to forgo the acoustic matting and simply to leave down old carpet and underlay and overboard above it. This may not get the same result but it is a lot cheaper and it will certainly help.