Ideas Library · Outdoor Structures
Rainwater Storage Built Into the Structure Itself
Rainwater storage designed as a piece of the garden building rather than as an object placed near it, suited to owners who want to collect from the roof without adding a second thing to look at.
Spaces:kitchen gardenback gardenallotment or work gardengarden studioservice corner
Style:practicalcontemporarynaturalisticarchitectural
Where this idea works
Where this idea works
Contexts this direction tends to suit — and, honestly, where it may not.
- Garden buildings whose roof area is already shedding water to a downpipe with nowhere to go
- Positions where a separate tank or butt would be prominent or in the way
- Structures with a base, side wall or bench that could take on the storage role
- Owners wanting stored water close to where it is actually used
Where it may not fit
Where it may not fit
- Existing buildings whose base or frame was not designed for the weight of stored water
- Very small roofs where the collectable volume would not justify built-in storage
- Owners who want storage they can move, empty or remove easily later
Planning
Planning considerations
- Put the store under the roof that fills it, because the point of the idea is that the collection run is short and invisible
- Water is heavy and its weight is permanent, so the element becoming the tank is a structural element before it is a container
- The published records treat a harvesting arrangement as returning to behaving as drainage whenever the store is full, so the overflow route is designed rather than assumed
- Debris and the first, dirtiest part of an event are intercepted before storage, which means the filter has to sit somewhere reachable
- Fitness of stored water for any particular use is a matter for the designer and the relevant authority rather than something the structure settles
Layout
Layout considerations
- A store built as a plinth raises the building, which changes the threshold and the step at the door
- A store built as a bench has to be the right height to sit on, which may not be the height that holds the most water
- The draw-off point wants to be where water is actually carried from, not where the tank happens to end
- Access for inspection and cleaning has to be planned into whatever the tank is disguised as, because a sealed-in store cannot be looked at
Materials & finishes
Materials and finishes to discuss
Named generically as starting points to discuss with professionals — not specifications, and not priced.
Consider:concrete plinth tanklined blockwork chambertimber bench casingfilter and first-flush deviceoverflow connection to drainagegravel surround
- A permanently wet chamber inside a structure is a different environment from the structure around it and needs to be isolated from it
- Freezing is a consideration for any store that holds water through winter, and a built-in one cannot simply be emptied and put away
- An overflow that fails discharges at the base of the building, which is the worst possible place for it
Maintenance & durability
Maintenance and durability questions
- Filters and first-flush devices need clearing on a regular cycle, and a store designed without access to them stops working quietly
- Sediment collects at the bottom of any store, and how it is removed has to be part of the design rather than a later problem
Professional review
What to ask a qualified professional
Bring these questions to a designer, contractor or the relevant qualified professional or authority.
- What load does stored water impose, and can the element intended to hold it take that permanently?
- Where does the overflow discharge, and can the site drainage accept it?
- How will the filter, the chamber and the sediment be reached for cleaning once it is built in?
- What separation from the mains supply and what labelling would a qualified trade require?
- Are there local requirements on rainwater storage, discharge or use that apply here?
More ideas
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