Why are safe trays required?
Safe trays are required as a means to prevent water damage to household units caused by storage water heaters.
When are safe trays required?
The ‘Acceptable Solutions and Verification Methods for New Zealand Building Code Clause G12 Water Supplies’ was amended on 1 January 2017.
The amendment means that if:
- you are installing a storage water heater (hot water cylinder), and
- you didn’t have one installed previously, and
- G12/AS1 is your nominated means of complying with the Building Code; then a safe tray is required with storage water heaters when installed in household units and occupancies adjoining household units.
Are safe trays required for replacement storage water heaters?
Installing a new storage water heater, including attaching the pipes, valves and seismic restraint, is new building work that is required to comply with the Building Code.
Replacing an existing storage water heater is considered an ‘alteration to an existing building’ under the Building Act. The Building Act has upgraded provisions for alterations. Requir8ing that after the alteration the building will continue to comply to at least the same extent as it did before the building work.
So where an existing storage water heater does not have a safe tray, and is replaced as an alteration to an existing building, then a safe tray is not required, due to the building only needing to comply to at least the same extent as before the alteration.
Are there other places that safe trays are not required?
Safe trays are not required in buildings that are not household units - unless the adjoining occupancy is a household unit. Buildings solely used as commercial buildings such as offices or warehouses do not require safe trays.
Safe trays are not required for non-storage water heaters, such as under-bench boilers/chillers and instantaneous water heaters.
What other options do I have for a new or replacement storage water heater where a safe tray is difficult to install?
If a safe tray is difficult to install, in either a new or replacement situation, other options can be discussed between the plumber or building designer and the owner of the building. Alternative solutions can include:
- locating the storage water heater outside
- using instantaneous water heaters.
What safe tray material is suitable?
The New Zealand Building Code G12/VM1 refers to ASNZS 3500.4, which states:
Safe trays shall be fabricated from:
- 0.60mm thick galvanized steel sheet complying with AS 1397 and having a minimal nominal zinc coating mass of 275 g/m2; or
- other materials not inferior to Item (a), under the conditions of use.
What safe tray waste/drain is suitable?
The safe tray must incorporate a drain with a minimum diameter of 40mm, with the drain made from material that is compatible with the safe tray material and capable of withstanding hot water overflow from the storage water heater under conditions of use.
Where should the safe tray drain discharge to?
Water tanks need to have an overflow pipe to discharge any overflow to a visible place within the same property that does not create a nuisance or damage to building elements.
The outlet of the overflow pipe should not allow entry by birds or vermin.
Can I use a safe tray that integrates a Temperature and Pressure Relief valve (TPR) overflow with the safe tray overflow?
Residences in the Selwyn District Council area tend to have wetback solid fuel heaters and solar water heating retrofitted. These systems are uncontrolled heat sources.
Discharge from Temperature and Pressure Relief valves (TPR) can be of considerable volume and temperature, and can continue for a considerable time. Therefore, Selwyn District Council strongly recommends design in line with the Acceptable Solutions of a TPR valve drain, in copper, discharging separately from the safe tray, to an appropriate place that does not cause damage to the building.
Building Consent applications which nominate an Alternative Solution in regard to safe trays with an integrated TPR overflow will be assessed, however any such design must demonstrate that the system is capable of withstanding high temperatures for a sustained length of time.