Isolation Valves: Where They’re Mandatory & Why Quarter-Turn Ball Valves Win
AS/NZS 3500.1 Clause 5.10 & 3500.4 Clause 5.9 – 2025 flexible hose rule explained + how many per bathroom
Isolation valves (also called shut-off valves or stop valves) are one of the most important yet under-estimated items in any plumbing installation. They let you isolate a leak, repair a fixture, or service a hot water system without draining the entire house. Skipping them is a common cause of callbacks and non-compliance.
Where Isolation Valves Are Mandatory (Direct from the Standards)
AS/NZS 3500.1:2025 Clause 5.10 – Cold Water Services
Requires an accessible isolating valve in these locations:
- At the property boundary or meter assembly (main isolating valve)
- Immediately before each fixture or appliance (toilet cistern, basin, shower, washing machine, dishwasher, etc.)
- On branches serving multiple outlets
- Upstream of backflow prevention devices
AS/NZS 3500.4:2025 Clause 5.9 – Heated Water Services (updated 2025 rule)
- Immediately upstream of the heater (cold inlet)
- Downstream of the heater (hot outlet)
- Before tempering valves / TMVs
- On recirculation lines (if fitted)
- New 2025 requirement: Every flexible connector/hose to a storage heater must have an isolation valve (prevents leaks without isolating the whole system)
All valves must be accessible (not buried, not behind fixed panels) and preferably quarter-turn ball valves for quick shut-off.
Why Quarter-Turn Ball Valves Win (And Why You Should Specify Them)
- Full bore – no pressure drop (unlike gate valves)
- Quarter-turn operation – fast and reliable (gate valves can seize)
- Long life – less wear, no gland packing leaks
- WaterMark approved – DR brass or DZR brass models are standard (e.g., Philmac, Philmac, Enware, Reece house brand)
Gate valves and globe valves are now rarely used in new work — quarter-turn ball valves are the deemed-to-satisfy choice for all isolating applications in the 2025 editions.
How Many Isolation Valves to Allow Per Bathroom (Practical Estimating Guide)
For a typical bathroom with shower, basin, toilet, and possibly bath:
- Toilet cistern → 1 isolation valve (cold supply)
- Basin → 1 or 2 (hot + cold, or one per tap if separate)
- Shower → 1 or 2 (hot + cold, or one per mixer)
- Bath filler → 1 or 2 (hot + cold)
Minimum safe allowance per bathroom:
- 4–6 valves (one per fixture supply + extras for branches)
- Conservative estimate (best practice): 1 valve per hot and cold supply line + 1 main branch valve per bathroom group → 5–8 per bathroom
Example for 4-bathroom house:
- 4 bathrooms × 5–8 valves = 20–32 valves
- Cost allowance: $20–$60 per valve (DR brass quarter-turn) + labour → $800–$2,000 materials total
Quick Compliance Checklist for Your Next Quote
- Use quarter-turn ball valves (not gate)
- Make them accessible (not behind tiles, not buried)
- Include on flexible hoses to heaters (new 2025 rule)
- Specify WaterMark approved DR/DZR brass
At SNZ Plumbing Estimating, we include every required isolation valve — no callbacks, no compliance surprises.
Have you ever had a job failed because of missing isolation valves? Drop a comment or DM us for a quick check on your next estimate!
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