Steel Tank Stands for Fire-Fighting Water in the Adelaide Hills

A raised tank of fire-fighting water is structural steel, not a garden project. A full 22,000 litre tank holds about 22 tonnes of water before you add the tank itself, so the stand, its bracing and its footings need to be engineered. In a bushfire prone area the stand should be non-combustible, which means steel or concrete. If any part of the tank or stand ends up more than 4 m above the ground, it needs development approval.

We had exactly this enquiry from someone designing a new home in the Adelaide Hills: a galvanised steel stand about 5 m high for a 22 kL fire-fighting tank, ideally designed so it could be clad later and turned into a double garage. Here is what we would want you to know before you get to the quote.

Why raise the tank at all

The CFS page on preparing your home and property says that to run a sprinkler system you need an independent water supply of 22,000 litres, and recommends an overhead water tank fitted with a gate valve and a canvas hose coupling or fire tank filler. Height gives you pressure without power: gravity-fed tanks with wide outlets let you fill buckets quickly and feed a portable pump. CFS also warns that electric pumps can lose power during a bushfire, recommends a petrol or diesel pump, says all fittings should be metal because plastic melts, and says not to leave exposed plastic pipe or hose that can burn.

The bushfire building rules

Ministerial Building Standard MBS 008 sets additional requirements for new houses and other Class 1, 2 and 3 buildings in designated bushfire prone areas, including a water supply for fire-fighting. For an above-ground tank, MBS 008 requires the tank and its support structure to be non-combustible, such as concrete or metal. The current version on PlanSA is Version 1, published 25 June 2020.

The volume you need, the outlet fittings and the access for CFS trucks depend on the bushfire overlay over your block and the conditions on your consent. Get those from your building designer or the council first, then design the stand around them. Do not guess them from a neighbour's setup.

When does a tank stand need approval?

Schedule 4 of the Planning, Development and Infrastructure (General) Regulations 2017 excludes some water tanks from development. Under clause 4(1)(g), a tank and any supporting structure is excluded only if it:

• is part of a roof-drainage system
• in a bushfire risk area, has a total floor area of no more than 15 m² and a total volume of no more than 60,000 L (10 m² and 40,000 L elsewhere)
• is located wholly above ground
• has no part higher than 4 m above the natural ground

A 22 kL tank on a 5 m stand is well over 4 m, so it needs approval. If you are building a new house anyway, the simplest path is to include the tank stand in the house application so it is assessed with the bushfire requirements it is meant to satisfy.

Designing the stand

Things the design has to answer before any steel is cut:

• The full load. Water at roughly 1 kg per litre, plus the tank, plus anything that sits on the platform. Ask the tank maker for the full weight and the base support the tank needs, because some tanks need a fully decked platform rather than beams.
• Wind. A tall tank on a tall stand catches a lot of wind, and Hills sites are often exposed. Bracing and footings are sized for it.
• Footings. Hills ground ranges from reactive clay to rock within one block. The footing design should come from the site, not a standard drawing.
• Corrosion. Hot-dip galvanised steel suits a structure that lives outside and stays wet around the outlets. Bolted connections keep the galvanising intact. Any site welding on galvanised steel needs the coating repaired.
• Access. Plan how you will reach the inlet, the outlet valves and the fire fittings without climbing the frame.

Designing it to become a garage later

Clad later into a double garage is a good idea, but only if the stand is designed for it from day one:

• Bracing versus doors. Diagonal cross-bracing is the cheap way to stiffen a stand, but it blocks the bay where a roller door would go. Plan the door openings first and brace around them.
• Cladding adds wind load. An open frame lets wind through. Clad it and the frame has to resist the wind on the walls as well, so engineer it for the enclosed case now.
• Girts and fixings. Leave cleats or fixing points for wall girts so cladding can go on without welding the galvanised frame on site.
• It is new work later. Enclosing it into a garage is building work in its own right and will need its own approval when you do it.

What to send us

The tank make and model with its full weight, the height you need, the bushfire requirements from your consent or designer, a photo or site plan of where it goes, and whether you want the garage option. We fabricate in our Mount Pleasant workshop and install across the Adelaide Hills, Mount Barker and the Barossa. For other one-off steel, see our metal fabrication page.