Noisy Pipes
Noisy Pipes can be quietened by several methods, most of which are of a similar nature. The amount of effect of each measure will vary, and for best results it is often desirable to combine a few measures.
Causes of Noisy Pipes
- Water turbulence due to high flow rate & sharp corners
- Transmission of sound along pipe from a noisy valve
- Waterhammer - sounds like rapid hammering
- Lightweight walls acting as sounding board
- Knocking - Pipe moving against restraints due to thermal expansion
- Rubber disc in valve oscillating - causes waterhammer or a foghorn-like noise
- Hiss caused by poor fill valve design
- Lightweight panels with pipes clipped to them can act as sounding boards.
Solutions
General Solutions
Wrap the pipe with lagging.
Box the pipes in. This provides a physical barrier to sound transmission, and creates a void that can be filled with rockwool or similar for damping and sound absorption. The heavier and stiffer the boxing, the more effective it is. Minimise and seal any gaps for best performance.
Lag the noisy pipe wherever it goes outside of where it is causing the noise problem. Eg lagging added in the loft will have some benefit on downstairs noise too.
Where there is already a physical barrier over the pipes
Draughtproof the barrier to eliminate air paths. To see how much difference this makes, open a double glazed window by a couple of mm.
If blocking all gaps is not a practical option, add strips of wood to make any sound travelling through gaps turn round corners. The more corners it has to turn, the more effective this is.
Add damping to the barrier. Eg fix on a rubber mat, carpet, 2 layers of cardboard or roofing felt, or other deadening material.
Replace the barrier with something heavier & stiffer.
Add a sound absorbent layer to the barrier, eg rockwool batts. This is not the same thing as a damping layer, rockwool gives both airborne sound absorption and some damping.
For existing boxing, it is possible to apply a 2nd layer of boxing with a sound absorbent between the 2 layers. Its not often this is necessary, but it might be desirable for internal soil stacks when total silence is wanted.
Specific Solutions
With waterhammer or foghorn noise, replace the rubber diaphragm in the valve or tap at the end of the pipe. This frequently cures it.
For knocking, replace metal pipe clips with plastic U shape clips. These open fronted clips grip the pipe less firmly, allowing it to move more easily, reducing or eliminating knocking. The other type of U clip, which is open at the rear and has 2 fixing points, allows slight lateral movement, which may be sufficient.
In some cases you can happily turn down the water flow rate with a valve, and this can have a big effect on some types of noise. If necessary, fit a valve to do this. This is well suited to toilet cisterns, where slightly slower fill is not normally a problem. This can often be enough stop waterhammer and foghorn effects, and much reduce hissing during filling.
Plastic pipe has some acoustic damping effect, uses less sharp bends, and does not transmit noise as much as copper.
For pipe under floorboards, a cheaper option to lagging is to place carpet offcuts onto the pipe and put the boards back. Carpet damps the pipes & acts as a barrier to sound transmission. The carpet should be wide enough to droop down onto the ceiling either side of the pipe.
If the pipe is clipped to a lightweight wall
Add damping to the wall, eg rockwool fill. Fire retardant rubber mat also works.
Replace thin sheet materials on the wall with thicker materials with better sound absorption.
Remove any clips attached to plasterboard alone, and reclip to where there are studs behind the PB. This is not normally a problem, but amplifies noise if it is.
Where pipe goes through holes in wood, sleeve the pipe with something flexible to stop direct sound transmission from pipe to wall structure.
Fit a 2nd layer of plasterboard to the wall, staggering the joints.
Untested
Slightly loosen metal clips to allow pipes to move very slightly, reducing knocking noises.
Prevention
Use plastic clips rather than metal.
Fit isolation valves, which assist maintenance and are also an easy means to reduce noise if it occurs
Choose plastic pipe over metal
Metal pipes that are barely big enough are noisier than bigger pipes with some flow margin.
Lag pipes.
Where not lagged, add occasional mechanical damping pieces to pipes, such as polystyrene blocks wedged under the pipe.
Avoid clipping pipes to lightweight walls when other routes exist.
When constructing a lightweight wall, 2 layers of plasterboard with staggered joint positions gives much better acoustic performance than a single layer. It is also more robust and gives longer fire protection.
Stud walls perform better acoustically if they're made from at least 2x4 studwork. Small sizes eg 1.5" x 2.5" tend to perform poorly in this respect.
If constructing a low cost lightweight wall without rockwoool fill or simliar, placing a concrete block on each horizontal noggin is a way to improve wall mass and reduce the sounding board effect to some extent. Placing a small piece of a damping material on top of this block will give the plasterboard panels some damping.
Materials
Materials sold specifically for soundproofing have a habit of being overpriced. In many cases its much cheaper to use standard diy materials.
Rockwool is a general purpose sound absorber.
2 layers of cardboard glued in place, or 1 layer of triplewall cardboard, is effective damping for sheet materials. 2 layers of roofing felt is more suitable where dampness may be encountered.
Be a bit cautious about using expanding foam as a damping material. It is effective damping, but expands with force and can cause damage.