Wrap it with acoustic insulation such as mineral wool or recycled polyester fibre and box it in with 2 layers of acoustic plasterboard.

£8-16 for 1-2 sheets of acoustic plasterboard. £10-30 or so for insulation but you'll probably have a load leftover.

move it to outside!

Concrete is good at deadening sound

little tip , stick some foam round the pipe clips if you use them , as pipe expands and contrates with heat these can make a noise , I use sheveks method .
I prefer internal pipes , keeps that additional heat in the warm envelope for a little longer :)

External soil pipes are easier for builders and easier to maintain, but they look terrible and can freeze in cold spells.

The most energy efficient solution is to route them all inside with air acceptance valves at the top. If ventilation is required to relieve positive pressure then a separate vent pipe can be run up the outside of the house or in a false chimney thereby keeping the ventilated pipe entirely outside the thermal envelope.

David

Thanks for all the info.

i'll have a look at the construction at the weekend, the pipe behind the wc (above the room) is in a void , I don' t think it vents outside.

did I say this is my son's house....................

Posted By: tonyConcrete is good at deadening sound

Rereading that brings another idea to mind. If the pipe is boxed in, you might be able to just pour some dry sand around it as long as the structure is strong enough.

Over here in italy I have just bought a foam bonded to lead product in a roll at about £20 m2 - designed for pipes it is 'heavy' but flexible and I reckon would have a better performance than your find - but I have no figures and no make without some work. Screw for scale! Let me know if you're interested.

Some feedback on this topic.
I have picked up Dykasol acoustic damping, used it around the pipes under the bath room (ceiling of would be spare bedroom). Also the surrounded with mineral wool and a layer of gips.
The Dykasol cut out a lot. About half. Cost 41 Euros for 5m for 110mm pipe. Not too hard to connect. Getting around bends, is maths and Dykasol do provide a simple guide that helps.
The mineral wool gips cut it again. Very very quite now, Full flush, shower running. I will add another layer of gips around pipe, for surety.
Also, if my case your looking at shower above, never forget the sound of water drumming on a floor.

Posted By: ShevekDoes anybody know why the NHBC would specify "unfaced" insulation to soil vent pipes?

Presumably because the facing (aluminium foil etc?) is likely to reflect noise rather than absorb it.

We have a soil pipe that passes through a similar construction in the corner of our downstairs bedroom. Even with the noise reduction, you can still hear the toilet being flushed, or rather the water rushing through. So we tend not to use that loo when anybody is staying in the bedroom. I'd go overboard on the insulation and mass etc.

Mineral wool will only offer so much sound reduction here. Adding two layers of Soundbloc drywall to the boxing helps loads but you will still have some leakage from the ceiling. You will really want to add mass to the pipe, not the boxing-in. Tecsound FT55 Acoustic Duct Wrap seems to be the best product for this. It has a soft felt material that lays on the pipe, then mass loaded vinyl, then foil. So it matches those building rules. Also, avoid pipe offsets as much as possible. They make a huge amount of sound.