Providing Acoustic Ceilings Between Flats
I often get asked what is the best way to sound-proof ceilings when newly converting flats? In my experience independent ceilings work best. You can remove old ceiling to put new joists between old to save space but that means you lose the soundproofing of the old ceiling.
- Caulk the old ceiling including ceiling rose and any cracks to make it air-tight.
- Wall plates to be wall-plugged and screwed to the walls. 6″ joists are usually enough to carry even quite a heavy ceiling. Or the steel framed system can be used. It’s important that there are no vibration bridges between the two, such as pipes or other services in the ceiling. This is not the same as a suspended ceiling!
- Acoustic fibreglass is to be hitched between the joists to deaden the sound within. Long nails can be left protruding near the bottom edge of the joists to hook the fiberglass over. Acoustic grade is heavier than normal thermal fibreglass but massively more expensive. I usually substitute the cheap thermal stuff and haven’t failed a test yet.
- Two layers of 13mm plasterboard screwed in place underneath, with joints caulked with acoustic caulk on both layers, joints offset. Or you can use acoustic plasterboard but it’s very heavy. A plasterboard jack makes life a lot easier. Otherwise you can use the old T pole method (a few poles just over ceiling height with a crossbar at the top and a diagonal bracket. These are used to wedge the plasterboard under the ceiling prior to fixing).
- Skim and paint.
- If you have access, also a good idea to caulk between the floorboards upstairs for extra airtightness, and fit decent underlay beneath the carpet.
Key points to remember are not bridging between the old and new ceiling, and airtightness. The independent testers will test for both airborn noise and floor-transmitted vibration.
If you have low ceilings already so lack head-space the resilient bars method is cheaper and quicker but less dependable. You have to be very careful not to pierce or connect with the floor above by the plasterboard screws, otherwise the resilient bars won’t work and vibration will be transmitted.
It’s all about the detailing. If you detail it well and fill all gaps really conscientiously then you should pass any test easily.
As a ball-park this might cost £500 for an average sized lounge or bedroom.
Beware though there are other steep costs to converting houses to flats, utility spits (gas, electricity, water) is just one but can cost over £10K. Thermal insulation to all outside-facing walls another.
A ball-park figure for converting an average semi or terrace to 2 x flats, in a simple layer-cake conversion, is £25 – £30K per flat. And that’s if it’s relatively straightforward.
If you wish to make existing floors to existing flats a lot more sound-proof you can try acoustilay acoustic matting. Not cheap but quite effective.