Anyone stored water in their roof cavity?

I’ve heard of flexible membrane tanks being used in the basement of houses for rain water storage but does anyone know of using one’s roof cavity?

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I briefly considered that, a small amount (to gravity-feed to toilets) using these flat tanks you fit on 4x4 roofs. In the end it was easier to use a normal pressure pump direct from the outside tank.

Other than that… not much. And besides, water weighs a lot, I’m sure there are limits involved that kick in very quickly :slight_smile:

You mean like a geyser? :stuck_out_tongue_winking_eye:

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Standard practice in older British and Irish houses.

I remember these header tanks that fed geysers.
I’m thinking more about using this space rather than the tanks installed outside. I don’t think these tanks are a pretty sight and they take up a lot of space…

I would be VERY careful. A 5000l tank weighs about 5 tons full… and even putting in small 500l tanks wouldn’t be a good idea. Chat to the architect first. The roof/ceiling isn’t normally designed to hold that sort of weight.

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In most cases I think roof trusses are pretty much on their design limits.

I think it can work if a house gets designed with that in mind right from the start, for starters a 5000l tank must be installed on a solid level surface which in this case probably means a concrete slab ceiling.

If you go with smaller tanks which can fit in a standard roof space, then the price goes up.

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Having built up a few years ago, custom roof trusses and all that, I learned that roof trusses are designed for a specific purpose.

Existing roof trusses, to go now and add a bladder afterward on top of those trusses, trusses that would have been a custom-made design with Engineering signoff on building plans originally, is not a good idea no.

If you insist on doing it, rather speak to roof truss experts.


I did a sort of a diy extension a few years back and I had to provide the truss company the plans, tiles I was going to use and specify if any geysers were going to be installed.

I specified I wanted to add solar and this was added into the design where they added an additional 20kg/sqm.

You can’t just go add tanks on the trusses.


Can be done however you need to keep the following in mind: water weighs 1kg per litre therefore keep the volume to the weight your ceiling can support, if you do have a truss roof then they are not designed to take a load on that bottom cord.

With that in mind keep it within reasonable volume and I would not bother with a truss roof unless you take professional advice.