Intro

A cast iron repipe replaces old cast iron soil and waste lines with new pipework. You do this when the system is corroded, cracked, noisy, or causing blockages. It stops leaks and odours, and it protects finishes. In this guide, you’ll learn when a cast iron repipe makes sense, how to plan it, and the best way to install it. We cover simple steps, UK sizes, safe demo, support spacing, fall, testing, and client communication. Use this as a field checklist. It saves time and avoids callbacks.

Quick Answer

A cast iron repipe is a full or partial replacement of failing cast iron drains. You assess with a camera, plan routes, demo in sections, and install new PVC‑u or no‑hub cast iron with correct falls, supports, and fire‑stopping. Most homes take 2–5 days with a 2–3 person crew.

Table of Contents

• When a Cast Iron Repipe Is Worth It
• Cast Iron Repipe: Step-by-Step
• Estimating a Cast Iron Repipe
• Tools, Materials, and Safety
• Common Mistakes and How to Avoid Them
• Communicating With Clients and Neighbours
• FAQ
• Conclusion

Key Takeaways

• Replace when pipes are cracked, scaled, or older than 50–70 years.
• Keep fall around 1:40 on horizontal runs; support every 1.2–1.8 metres.
• Typical sizes: 32–50 mm wastes and 110 mm soil stacks.
• Small flats: 1–2 days; two‑storey houses: 2–4 days; larger stacks: 3–7 days.
• Test with a 3 m water head or 0.2 bar air test before closing up.

When a Cast Iron Repipe Is Worth It

Old cast iron is tough, but it does fail. You should consider a cast iron repipe when you see repeat blockages, heavy rust scale, cracked hubs, or leaks on joints. Strong sulphur smells and stained ceilings are also common signs. Age matters too. Many systems over 50 years are near the end of life.

On most jobs, start with a camera survey. Run 32–50 mm wastes and the 110 mm stack. Note bellies, offsets, and root ingression. Mark exact problem points to avoid unnecessary demo. If more than 30–40% of a stack is compromised, a full stack repipe is usually cheaper long‑term.

Think about sound. Cast iron is quiet. PVC‑u is lighter and faster, but it can be noisier. In flats and hotels, you might keep cast iron on the main stack and use PVC‑u on branch runs. Always check the building’s fire rating and acoustic needs before you choose.

Cast Iron Repipe: Step-by-Step

Follow these steps to deliver a clean cast iron repipe with fewer headaches.

1. Survey and Scope

   • Camera the lines. Map fittings, floors, and riser positions.
   • Confirm sizes: 32 mm basin waste, 40 mm shower/kitchen, 50 mm commercial branch, 110 mm soil.
   • Identify fire‑rated floors and walls. Note any 60‑minute or 120‑minute barriers.

2. Plan Routes and Isolation

   • Mark cut points and coupling locations every 1.5–3 m.
   • Agree water and WC downtime windows (2–8 hours blocks).
   • Book skips and protection. Plan lifts for heavy sections.

3. Protect and Set Up

   • Sheet floors and lifts. Build dust containment with polythene.
   • Fit negative air if cutting indoors. Keep noise windows clear for neighbours.
   • Stage materials. Pre‑cut 110 mm lengths where possible.

4. Safe Demo of Cast Iron

   • Support above and below each cut with riser clamps.
   • Use a chain‑type snap cutter where possible. It is fast and low dust.
   • For stubborn sections, use an angle grinder (125 mm diamond) or a recip saw with 10–14 TPI blades. Cut in small passes.

5. Layout and Dry Fit

   • Maintain fall around 1:40 (about 2.5%) on horizontal runs.
   • Use long‑sweep bends on 110 mm soil. Avoid tight 90° on waste.
   • Check clearances through studs and joists. Fire collars ready at penetrations.

6. Install New Pipework

   • Option A: PVC‑u soil and waste with solvent welds; use rubber transition couplings to old cast iron.

• Photograph work. Label cleanouts at 6–10 m intervals on long runs.
• Provide as‑built sketch with sizes and access points.
• Brief the client on care, access, and warranty.

Estimating a Cast Iron Repipe

A solid estimate starts with clear units. Count stacks, floors, branch fixtures, and penetrations. A small flat (one bathroom) often takes 1–2 days. A two‑storey house with two baths may take 2–4 days. A single multi‑storey stack can run 3–7 days depending on access and finishes. Plan a 2–3 person crew for safe handling.

Price materials by size. Typical UK soil is 110 mm. Wastes are 32, 40, and 50 mm. Add 10–15% for fittings and couplings. Include fire collars for each 110 mm penetration. Add acoustic lagging if required. For labour, add time for containment, demo, cutting, and test. Don’t forget patching and making good.

Document assumptions clearly. List working hours, water shut‑offs, and any provisional sums for hidden sections. Many contractors win work by showing a clean process. Voice notes and site photos help. Tools like Donizo let you capture details on site, turn them into a branded proposal, send it for e‑signature, and convert to an invoice in one click. If you’re also looking to streamline professional proposals, or to manage change orders and project timelines, build those processes into your estimate notes.

Tools, Materials, and Safety

Having the right kit makes a cast iron repipe smoother.

Tools

• Chain‑type snap cutter for cast iron.
• Angle grinder (125 mm diamond) and a recip saw with 10–14 TPI blades.
• Pipe laser or level for 1:40 falls; tape, markers, and a camera.
• Riser clamps, M10/M12 anchors, and banded couplings (stainless).
• Wet vac, pump plugs, test bungs, and a pressure gauge.

Materials

• 110 mm soil, 32/40/50 mm waste (PVC‑u) or BS EN 877 cast iron.
• Long‑sweep bends, tees, access caps every 6–10 m.
• Rubber transition couplings and solvent cement (for PVC‑u).
• Fire collars/wraps and intumescent mastic.
• Acoustic lagging where needed.

Safety

• PPE: eye protection, gloves, hearing, and a P3 respirator for dust.
• Manual handling: a 2 m cast iron section can weigh 25–40 kg. Use two people.
• Support before cutting. Never let a riser hang.
• Dust and spark control. Shield glass, sprinklers, and alarms.
• Follow UK Building Regulations Part H (drainage) and Part B (fire). Confirm with Building Control.

Common Mistakes and How to Avoid Them

• Flat or excessive falls. Keep around 1:40. Too flat causes blockages. Too steep lets water outrun solids.
• Poor support. Space hangers properly: 1.2 m for PVC‑u horizontal, up to 1.8 m for cast iron. Fit riser clamps at floor levels.
• Tight bends. Use long‑sweep fittings on 110 mm. Add access caps before changes of direction.
• No expansion allowance on PVC‑u. Leave about 10 mm per 3 m. Use slip joints.
• Mixing metals without proper couplings. Use stainless banded or specified transition couplings.
• Skipping tests. Always water or air test before boxing in. Record results and photos.
• Forgetting fire‑stopping. Fit tested collars on each 110 mm floor or fire wall. Seal gaps fully.
• Poor protection. Use polythene, hardboard, and dust control. It prevents expensive redecoration.

Communicating With Clients and Neighbours

A cast iron repipe disrupts daily life. Explain it clearly. Show the plan, the shut‑off times, and the noisy stages. For flats, give 24–48 hours notice to neighbours. Use signs on lifts and lobbies.

Set expectations: water and WC downtime may be 2–8 hours in blocks. Demo might be 1–2 days. Testing takes 30–60 minutes per stack. Tell clients where access panels will be. Note any finishes that need making good.

Keep changes documented. When you find hidden branches or rotten sections, log it fast. If you use platforms such as Donizo, you can send a quick updated proposal and get an e‑signature the same day. This pairs well with clear change order templates and strong invoice terms.

FAQ

How long does a cast iron repipe take?

Most homes take 2–5 days with a 2–3 person crew. A small flat can be 1–2 days. A larger multi‑storey stack may run 3–7 days. Access, fire‑stopping, and finishes can add time.

Should I replace with PVC‑u or new cast iron?

Both work. PVC‑u is lighter, cheaper, and quicker. It can be noisier. No‑hub cast iron (BS EN 877) is quiet and robust but heavier and slower to fit. In flats, many installers use cast iron for stacks and PVC‑u for branches.

Do I need to replace the whole stack?

Not always. If damage is local, you can replace sections with proper transition couplings. If more than 30–40% is failing, a full cast iron repipe is usually best. It avoids repeat visits and extra making good.

How do you test the new pipework?

Do a water test with a 3 m head for 15 minutes, or an air test at about 0.2 bar for 5 minutes if permitted. Check all joints and fittings. Record results with photos before closing.

Do I need building control approval?

In general, yes for significant drainage alterations. Follow Part H for drainage and Part B for fire‑stopping. Check with your local Building Control. Keep documentation and test records for sign‑off.

Conclusion

A cast iron repipe fixes chronic leaks, odours, and blockages. Plan the route, control dust, keep the fall at 1:40, support properly, and test before closing. Clear client communication prevents friction.

Next steps:

• Walk the job and map every branch, floor, and penetration.
• Build a simple, line‑item proposal with photos and testing notes.
• Schedule shut‑offs and noise windows, then order fire‑stopping parts.

If you like fast paperwork, tools like Donizo help you capture site notes by voice, send a branded proposal for e‑signature, and invoice in one click. Do the basics well, and your repipes will run smoother every time.