Soundproofing: The Key Rules

Floors

If you are building an intermediate floor – that is one that acts as both a floor for the room above and a ceiling for the room below – the Building Regulations now demand that you have to take some account of sound transmission. Whether the floor is made of timber or masonry, you have to make adaptations.

If you are building a traditional timber joisted floor or one made of engineered timber beams, you must place some insulation into the floor void and also use a ceiling board that is slightly heavier than standard. The key here is to specify one which is at least 10kg/m² in weight: every manufacturer has a product to suit (helpfully, British Gypsum’s plasterboard is called WallBoard TEN). The insulation would normally be 100mm thick — you don’t want to pack it out at full depth. The hoped-for decibel reduction with this design is 40dB, as compared to around 35dB for unimproved floors.

That gives you a modicum of soundproofing but if you want to improve it still further there are various other options.

• The simplest is to fit a good carpet and underlay on the floor above, as this will dampen airborne sound and greatly reduce impact sound as well.

• If you want a hard floor surface, you can use a sound-deadening underlay. There are several manufacturers: perhaps the best know is Acoustilay.

• You can build a floating floor. There are numerous proprietary acoustic floor systems on the market; they are rated either lightweight – aimed at impact noise mainly – or heavyweight. The heavyweight ones are usually made up of layers of heavy board products with names like SoundPlank. Overall, with attention to flanking sounds as well, heavy floating floors will add about 5dB to decibel reduction, but they add 50mm to your floor depth.

• Another improvement is to use resilient bars attached to the underside of the joists. These separate the ceiling board from the floor — isolation is an important principle in soundproofing. The best way of building isolation into a floor is to separate the ceiling joists from the floor joists, but this makes for a lot of extra work and a very deep void.

• You can pour a gypsum screed onto a timber floor to give it the characteristics of a masonry floor. Self-builders have pioneered the use of gypsum screeds on ground floors but the use of them on intermediate timber floors is relatively new. Note that if you go down this route, the floor needs to be designed to hold the extra weight — it’s not an afterthought! The business specialising in this is Screedflo GB (screedflo.co.uk).

If you fit a masonry intermediate floor, you are working with a high-mass material that absorbs sound well. However, it is still important to finish the floor correctly: the surface requires a screed in order to seal it.

Also, downlighters don’t do much for soundproofing. If you are concerned about noise coming up through the holes, then fit acoustically rated downlighters; try Snaplite (snaplite.co.uk).

Walls

Walls are generally less of a problem in individual homes. The basic guidelines required by the Building Regulations are not very exacting. If your walls are masonry, you simply have to plaster them. If they are timber or steel stud, you are required to either double-board each face, or to place mineral wool within the wall and to finish the walls with a 10kg/m² board — similar to the ceiling board used under timber floors.

As with floors, there are a number of improvements that can be made to stud walls. One popular with self-builders is to use Fermacell board rather than plaster - board. Fermacell (fermacell.co.uk) is a much heavier board which needs very little finishing and it’s particularly popular with people wanting to do their own finishing without having to hire a plasterer.

Another tip is to design bedrooms with fitted cupboards built into the dividing walls, where possible. It’s a great way to build in soundproofing at no extra cost.

Bear in mind that a bedroom is only as soundproof as its weakest link and that’s usually the door. You could go to the expense of fitting an acoustic doorset, but if you have a teenage drummer, it’s still not really going to fit the bill as well as an outhouse.

Further reading:

• Solutions For Insulating Walls
• Choosing Your Floor Structure
• A Guide to Internal Finishes