Cast iron soil stack replacement in Bristol terraces

A soil stack is the big pipe that takes waste from the toilet down into the underground drain. On most Bristol Victorian terraces it runs down the back wall of the rear wing, often beside the bathroom that was added over the kitchen years after the house was built. A lot of those stacks are still the original cast iron, or cast iron put in when the bathroom first went in.

Cast iron lasts a long time, but not forever. Easton, Bedminster, Totterdown and Fishponds have thousands of these homes, and stacks fail every year. If you live in BS5, our Easton area page explains the housing we usually work on there.

How to tell your soil stack is failing

Sign	What it usually means
Rust streaks down the wall below a joint	Joint has cracked or the seal has gone
Damp patch inside next to the toilet	Branch connection or the stack is leaking into the wall
Smell of sewage outside, near ground level	Crack or failed joint letting gases out
Flaking, bubbled paint on the pipe	Pipe wall thinning from rust
Toilet gurgles when the bath empties	Stack vent blocked or too small
Green moss or algae on the wall	Water has been escaping for a while

Cast iron fails from the inside as well as the outside. Rust and a hard crust of urine scale build up inside the pipe. In a hard water city that crust tends to be thicker, and Bristol Water says its whole supply area has moderately hard to very hard water. Over decades, the build up narrows the bore of an old stack and can trap paper, which is one reason blockages show up in the stack rather than the drain.

Repair or replace

Repair makes sense when:

• One joint or one short length is cracked.
• The rest of the pipe is sound when tapped and looked at.
• The stack is the right size and properly vented.

Replace makes sense when:

• More than one section is leaking.
• The pipe is thin and flaking along its length.
• A new bathroom is going in and the branch connections need to move.
• The stack has been cut short and does not vent above the windows.

Most replacements on Bristol terraces swap cast iron for plastic soil pipe. It is light, sealed with ring seals, and does not rust. In some places a cast iron look plastic or new cast iron is used for appearance.

Conservation areas and listed homes

Bristol has 33 conservation areas, with stricter planning controls than other places. Clifton and Hotwells is the best known, but several other inner suburbs have one too. You can check your street on the council’s Know Your Place map.

A few points to bear in mind:

• Stacks on the back wall, out of public view, are usually treated as a repair when replaced like for like.
• A stack on a front or side wall that faces the street is more sensitive. The council may expect a cast iron or cast iron look finish.
• In a listed building, changes to historic fabric can need listed building consent, even for drainage.

If you are unsure, email the council’s conservation team before work starts. Their details are on the conservation areas page linked above.

What the rules say

Soil stacks are covered by Part H of the Building Regulations in England. In plain terms, the stack must:

• Be big enough for the toilets connected to it.
• Have access points so it can be rodded if it blocks.
• Be vented to the open air at a safe height, away from windows.
• Connect to the drain with a proper bend at the base.

If an air admittance valve is used instead of an open vent, it must be fitted where it is allowed and still work. These are common in loft conversions, where a stack has to be extended.

What the job involves

On a typical two storey Easton terrace, replacing a stack goes like this:

1. Check the stack, the branches and the drain connection at the base.
2. Agree access. On a terrace this is usually a ladder from the back yard, or a small tower if the rear wing is tall.
3. Take the old cast iron down in sections. It is heavy, so this is done with care.
4. Fit the new stack with brackets into sound masonry. Pennant stone walls can be crumbly, so fixings are chosen to suit.
5. Connect the toilet branch and any bath, basin or shower wastes.
6. Test with water from each fitting and check every joint.

Inside the house, the toilet may need to come off for a short time to connect the new branch.

Linked problems

A failing stack often goes with other issues:

• A smell in the house, covered in our guide to drain smells.
• A blocked drain at the base, covered on our blocked drains page.
• A bathroom that needs replacing anyway, which is a good time to sort the stack.

Our bathroom plumbing page explains how we plan stack work alongside a new bathroom.

What affects the price

We do not publish a figure. The price is confirmed after a look at the job. The main factors are the height of the stack, whether scaffolding or a tower is needed, how many branches connect to it, the finish you need for a conservation area, and the state of the drain at the bottom.