Can somebody please explain waste pipe sizing

[Chiz]

Hello

I've done plumbing in my house with copper water pipes before. 15mm is 15mm and 22mm is 22mm.

I now need to re-do the waste pipes in my bathroom due to a change in layout. I'm a bit confused with the standard sizing for waste pipes.

I've got the excellent Collins DIY reference manual. It states these sizes for waste pipes:

32mm for basin
40mm for showers and baths

When I go to B & Q that is what is on sale.

However, I have measured the pipes in my bathroom as follows (with calipers):

Shower waste - 43mm outside diameter
Bath waste - 56mm outside diameter (the shower waste connects to this)

As far as I know, the 56mm is not standard. I plan to cut a section of this and replace it with 40mm pipe.

Now I've been to my local plumbing merchants and they have sold me replacement pipe, T-pieces, corner pieces and a reducer to connect the new pipe to the 56mm pipe. All for solvent joining.

The pieces they have sold me are the correct sizes. I've measured the replacement pipe and it is:

43mm outside diameter
38mm inside diameter
It says 1.5 inches on it (which works out at 38mm, so internal diameter)

The point to my question is: are my pipes imperial sizing, or are they actually metric 40mm pipes? i.e. is 40mm not actually 40mm but 43mm OD / 38mm ID?

The reason why I ask is so that I know what to ask for when going to plumbing merchants.

Confused!

 

[alan8376]

One tip!

Although I can't answer the problem, please be aware when purchasing the waste pipe, as it differs slightly depending on whether you are fitting sliding joints or the glued type!

Suggest taking the joint with you, then you can double check!

 

[ChrisR]

As Alan says, stick to one system, oryou'll find the diameters do vary. The compression style fittings usually fitt all the close ( ie inch and a quarter, or inch and a half, derived ) ones.

WHy reduce the pipe size - I wouldn't. Bigger is quicker.
Max for 32mm is 1.2m iirc. Longer lengths need bigger pipe.

 

[Softus]

The BS for copper tubing specifies the outside diameter, whereas waste pipe is specified by inside diameter, so different brands (and batches) have different O.D.s.

BTW, 22mm O.D. copper is sometimes 3/4" I.D., which is most definitely not the same.

 

[Goldspoon]

Solvent pipe is a different diameter to push fit pipe. Stick to one system throughout.

If you have to mix the two (e.g. solvent pipe comes out the bathroom floor but you want to use pushfit) then you can buy a converter (solvent at on end, pushfit at the other)..

Pipe is usually advertised as 1 1/4" and 1 1/2" or might be advertised as 32mm or 40mm.

 

[mickyg]

usually find solvent weld waste pipe fittings from diy stores have different dimensions then those in the average home, i think its something to do with measuring the outside instead of the inside or whatever. just stupid if you ask me. usually anything you get from a plumbing merchants will match what you have in your house...so the moral of the story is don't buy waste pipe fittings from diy stores!
anyway, now screwfix is open sundays & bank holidays there no need to go to focus rip off anymore anyway

 

[LUNAT]

HI


use 40mm gluefit waste pipe for bath .simple.