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Hi all I'm about to put in a concrete pad for an external water tank that will weigh 3 tons when full. This will be the biggest concrete job I've tackled and I'd appreciate your input please. The top soil has been dug away and the pad will sit on the surface of very heavy clay sub soil (currently also supporting the foundations of our self-build house). Dimensions of the pad are 2700mm square and 125mm thick. A C40 mix seems to be best for septic tanks so I'm assuming the same for this. I'll be mixing it myself, and I plan to add grid rebar. My questions are: 1. should I put down membrane and gravel layer first? If so, can I use a random mix of rocks and stones (we have plenty on site)? 2. there's currently a layer of soupy churned up clay on the surface, is it best to remove this first? 3. I've found variations online for a C40 mix, can anyone tell me the correct mix? 4. If necessary could I pour the slab in two sittings? TIA, any other suggestions welcome.

Hi, I've been assuming that I'd put the mains water tank in my attic along with a grey water header tank. I was just reading an old Passive House Plus magazine (issue 15 Ireland page 37) and noted one builder put the water tanks for his development in an insulated shed? at ground level so it can't burst and drain water through the house. It got me thinking....are there any pros/cons to siting the tank in the attic (water pressure?) vs at ground level provided space can be found for it. Would you put it in a shed at the back of the garden or a garage? I'm planning to use PEX but if the connection to the attic tank dislodged or failed, that's a lot of water in a timber framed house to lose.... Thoughts?

Hi guys, Got a question I think one of you guys might be able to answer albeit not really a build related question: Do I need this cold water tank in my commercial property? Here is the background... I have a business premises which is basically a commercial unit that has had offices/kitchen/storage built into it, so when it was built in the early 00's it was just an open plan unit with a male and female WC, above this "toilet block" is a cold water tank, it must be about 200/250litres (based on it's size compared to an oil drum which is 205litres). We would like to develop the area above the toilet block to tie it into the mezz storage level we already have but the tank is bang smack in the middle for weight loading reasons and it really makes the space useless. All that is fed from this tank is the two toilets. It would be a simple case of cutting the two pipes that go to the tank and join them somewhere downstairs thus making the toilets mains fed. Apart from the obvious issue of if the water supply is cutoff we would only have a cistern full of water for each toilet to flush is there any reason why we could not remove this tank? I can think of no logical engineering reason other than that the valves in the cistern might not take mains pressure (although they should) but I am fitting a PRV to the system due to a new 15litre Ariston water heater we have installed which requires the incoming pressure to be no higher than 3bar so I can reduce the supply to the whole property with the Honeywall valve I have already purchased. The reason I am asking and not just doing, is because this is a commercial property and occasionally Scottish Water do make system checks of our water system to ensure we are in compliance (non-return valves before water heaters and so on). If anything I see a tank as a liability for many reasons. Is this tank a throwback to an older plumbing code?