Plumbing Stack Replacement In Older Buildings

Every apartment in a vertical line shares a stack: one set of pipes carrying waste down and, in older buildings, water up.

When that pipe reaches the end of its life, every apartment on the line is affected, and there is no way to do half a stack.

Knowing when it is due

Repeat leaks on the same line. One leak is an event. Three in two years on the same stack is the pipe telling you.

Cast iron gone thin. Cast iron waste stacks in buildings from the middle of last century corrode from the inside. They fail at the base first, where the flow is heaviest, and in horizontal sections where waste sits.

Galvanised water pipe with dropping flow, which is the [water pressure](/blog/water-pressure-problems-in-apartments) complaint arriving building-wide rather than in one apartment.

Recurring blockages in one line with nothing obvious causing them, which usually means the bore has narrowed or the pipe has deformed.

A camera inspection showing scale, corrosion or displaced joints. This is the evidence that turns a suspicion into a capital works item, and it is worth doing before the first big leak rather than after.

What the work involves

Access to the stack is through a duct, and in most buildings that duct is behind a wall in a bathroom or a kitchen.

Which means opening walls in every apartment on the line, working in each one, then making good. The plumbing is the shortest part. The access, the waterproofing and the reinstatement take longer and cost more.

Where the bathroom is being opened anyway, it is frequently the right time to do the [waterproofing](/blog/waterproofing-you-never-see-the-membrane-under-every-wet-area) and the tiling, because doing it later means opening the same wall twice.

How disruptive it actually is

Each apartment on the line loses water and drainage for a period, usually measured in days rather than hours.

Bathrooms are out of use. There is noise, dust and trades in the apartment. Tenants may need to be relocated for part of it, and owner occupiers need somewhere to shower.

Planning that honestly, with dates per apartment and a realistic duration, is the difference between a difficult job and a disaster. Underpromising on the timeline is the most common mistake, and it destroys the goodwill needed for the rest of the stack.

Options

Full replacement in modern materials. The complete answer, the most disruptive, and the longest life.

Relining, where a liner is installed inside the existing pipe. Much less disruptive, no wall opening in many cases, and it suits waste stacks whose walls are still structurally sound. It is not an option once the pipe has lost too much material, and it does not solve joint displacement.

Rerouting the stack outside the wall or in a new duct, which occasionally suits a building where access is impossible.

Partial replacement of the worst sections, which buys time and leaves the rest of the pipe at the same age.

A camera survey is what tells you which of these is actually available.

Paying for it

This is a capital works item, not a maintenance one. It belongs in the capital works fund and the plan, and the buildings that cope with it well are the ones that saw it coming five years out.

Buildings that discover it during an emergency leak face a special levy and a much worse programme, because the work then happens under time pressure.

Doing it once

The single best decision on a stack job is to open the wall once.

Plumbing, waterproofing, tiling, electrical relocations and make good sequenced as one job by one team, rather than five contractors booked separately and each waiting on the last. That coordination is the point of [one contact for the whole building](/blog/one-contact-for-the-whole-building-the-case-for-consolidation).

Ample runs stack work with the plumbing, waterproofing, tiling and carpentry under one programme, so each apartment is opened once and closed once.