110mm soil pipe sizes and fittings: bends, branches and vent cowls

What is soil pipe, and where does it go?

Soil pipe is the above-ground stack that takes toilet waste down the building and into the underground drain. It runs up the wall or inside a boxed-in duct, with a branch at each floor where a toilet or a waste pipe joins it, and it finishes at the top with a vent. The above-ground category sells it in white or black, which is the colour you will see on the outside of most houses.

Its partner is underground drainage, which is terracotta, made to be buried, with its own fittings. Soil pipe stays above ground and underground pipe below it. Our guide to underground pipe and fittings covers the buried side, and the two systems meet at the foot of the stack.

What sizes does it come in?

The soil pipe here is 110mm, sold in 3m lengths as a plain end pipe and a socket end pipe. That is the standard size for a WC connection: in the sizing table in our waste pipe guide, a WC connection is 110mm pipe with a 6m maximum branch and a fall of at least 18mm per metre. If you are matching an old stack, measure across the existing pipe first, or bring an offcut to the counter.

Part	What is here	Colours
Pipe	110mm, 3m plain end or 3m socket end	White, black
Bends	90° and 135°, standard and double socket	White, black
Branches	92.5° and 135°, standard and triple socket	White, black
Connector	Double socket pipe connector	White, black
Access fittings	Pipe, tee and 87.5° bend	White, black
Boss, clip, vent cowl	Strap on boss, pipe clip, vent cowl	White, black

Which bend or branch do I need?

A 90° bend turns the pipe through a right angle, and a 135° bend turns it through a gentler angle. Two 135° bends together give an offset that moves the stack sideways with gentle turns, which is the neater choice where the layout allows. Both bends also come in double socket versions, so pick by the sockets you need at that point.

Branches bring a toilet or a waste pipe into the stack. The 92.5° branch joins at close to a right angle, and the 135° branch joins at a shallower angle. Each also comes in a triple socket version. Count the pipe ends meeting at the joint and choose the branch with the sockets to match. A branch sits in the stack at each floor, so work out the floor levels and the toilet outlet height before you order.

What are the access fittings for?

Access fittings put a rodding point in the stack, so a blockage can be cleared through the access point. The range has an access fitting pipe, an access fitting tee and an access fitting bend at 87.5°. An access plug is listed with them. Put the access point where you can reach it with a rod, clear of the finished boxing.

How do smaller waste pipes join the stack?

A strap on boss takes the smaller waste pipes, from a basin, bath or shower, onto the soil pipe instead of a full branch. The boss goes on the stack and the waste pipe then connects to it. Tell us the size of the waste pipe you are connecting, because the boss has to match it, and check whether your run is push fit or solvent weld. Our guide on push fit or solvent weld shows how to tell.

Push fit or solvent weld for soil pipe?

This range is push fit. Each socket holds a rubber ring and the pipe pushes in by hand, so the joint can be taken apart again. Soil pipe is also made as solvent weld, where the socket is glued and the joint is permanent. Use one method on a joint, so check what is already on the stack. If it has been in for years, bring an offcut or a fitting so it can be matched by eye.

Does the stack need a vent?

Yes. The stack has to breathe. Cap it with the vent cowl so the traps keep their water seal. The vent cowl caps the open top of the stack and lets air in and out. Building regulations govern where a stack must terminate and when a valve is allowed, so check with building control for new work.

How often does the stack need clipping?

Support the stack with pipe clips fixed to a solid wall. For a WC run our waste pipe guide gives clips at 900mm horizontally and 1.2m vertically, with a clip within 150mm of each fitting, which is where the weight hangs. Clip first and finish the boxing afterwards.

What do I count before I order?

• The height of the stack from the foot to the vent, which gives the number of 3m lengths, with the last one cut to fit.
• Each floor where a toilet or waste pipe joins, which gives the branches and bosses.
• Every change of direction, which gives the bends, and every length you have to join, which gives the connectors.
• Clips for the whole run, and a vent cowl for the top.
• The colour, white or black, so that every part of the stack matches.

Work from a sketch of the stack with each floor marked, and the list falls out of it.

How do I get it?

Collect free from the Liverpool showroom at Unit 7 The Boxworks, Heysham Road, L30 6UR, open Monday to Friday 7:30am to 4:30pm and Saturday 7:30am to 1pm, to trade and public. Delivery is priced by postcode and shown on each product page and at checkout. Check delivery to your postcode before you order 3m lengths. Ring us on 0151 525 4488 with the fittings you need, and bring an offcut if you are matching an old stack.