Wed, 10 Jun 2026 09:14:46 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309453#Comment_309453 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309453#Comment_309453 Wed, 08 Oct 2025 12:52:52 +0100 wookey
The supplier tells me to install a 150mm deep reinforced concrete base (600mm wider than the tank - i.e 300mm all round). Which is fine, but I'm wondering if there is a lower-carbon way of doing this? Can one make a strong-enough base to avoid settling and potential damage to the tank base without just pouring 0.6m3 of concrete?

Concrete is about 380 kg/m3 so this would be 228KgCO2e, or approx one-way flight Stansted to Barcelona. It feels like there should be a better way.

Maybe the way driveways are made with an MOT subbase, and a solid perimeter to avoid spreading.
The point loading is very much lower with the tank (1.54m2 vs 0.09m2 for the tyres of a van of similar weight - i.e 1/17th of the load). I'm not sure what surface material to use to avoid risk of puncturing over time.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309454#Comment_309454 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309454#Comment_309454 Wed, 08 Oct 2025 13:54:30 +0100 owlman https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309457#Comment_309457 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309457#Comment_309457 Wed, 08 Oct 2025 16:49:04 +0100 djh
But if your ground is fairly solid and rigid then I'd think that a foot of sharp gravel would be as much use as a foot of concrete. And reinforcement, seriously? Some sort of membrane + sand to prevent puncturing the tank base?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309458#Comment_309458 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309458#Comment_309458 Wed, 08 Oct 2025 16:52:34 +0100 djh https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309460#Comment_309460 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309460#Comment_309460 Wed, 08 Oct 2025 19:58:55 +0100 Nick Parsons https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309461#Comment_309461 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309461#Comment_309461 Wed, 08 Oct 2025 20:20:30 +0100 djh ]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309462#Comment_309462 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309462#Comment_309462 Thu, 09 Oct 2025 11:50:50 +0100 WillInAberdeen
https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18341

As was said, the pressure on the ground (2tonnes/m2) is not an issue here, much less than a human footprint. It's more about the risk of differential settlement where one part of the base gets compacted over time more than another part, as the tank fills and empties, and maybe as rainwater moves underneath it. Then the tank weight might end up on uneven ground and it would tilt, or even split.

The proposed slab is to act as a ground beam and transfer the loads from any unsupported points, to well supported points (which is why it has reinforcing)

The tank manf hasn't seen your site ground condition so has to give CYA guidance that works anywhere. (We're in the same position, and know less about how the tank is built and how accommodating is base is!)

If you're willing to take some limited risk of it tilting/splitting/leaking (what damage could that cause, where it is located?) then dig a hole down to undisturbed subsoil, fill it back up with well compacted hardcore, install the tank and keep an eye on it. If you can find some old paving slabs, they would be good to go on top of the hardcore layer and stop any pokey-up stones from poking the tank.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309466#Comment_309466 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309466#Comment_309466 Fri, 10 Oct 2025 16:39:14 +0100 wookey The plastic is about 10mm thick. Rotomoulded.

The ground is the far corner of the garden, pretty-much undisturbed since at least 2008. Clay-based soil. Nothing bad happens if the tank leans or leaks (except that if it's bad enough I have to do this again in 10 years, better).]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309474#Comment_309474 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309474#Comment_309474 Fri, 10 Oct 2025 18:01:20 +0100 Peter_in_Hungary
I would go with the manufacturers recommendations.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309479#Comment_309479 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309479#Comment_309479 Fri, 10 Oct 2025 21:11:23 +0100 djh https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309495#Comment_309495 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309495#Comment_309495 Sun, 12 Oct 2025 19:39:58 +0100 revor Posted By: djhBasically dig a deep enough hole and fill with hardcore and the problem goes away. Piles and beams are for if you can't dig for some reason (TPO).

It is important that when digging down you do not disturb the ground at the level of where the hardcore meets the bottom of the hole. The ground will be compacted over the years and will form an excellent subbase for well compacted hardcore. Around here the BCO is very particular that the base of excavations prepared for concrete pours are flat and solid and they don't tolerate digger bucket tooth grooves. Might be overkill for your tank but the principle holds well. Topping the hardcore with flags is a good idea, helps distribute the load, look better more a finished look and inhibit weeds that would otherwise grow around the base of the tank.
I use a redundant 3600 l silage tank to collect rain water and I used to pump it up (ca 7m) to our growing area, that is until I worked out that it cost a bit more in electricity to drive the pump than the cost of domestic water.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309496#Comment_309496 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18362&Focus=309496#Comment_309496 Mon, 13 Oct 2025 10:08:36 +0100 fostertom
The advent of 'free' renewable electricity changes the conventional (50yrs?) environment-conscious rules-of-thumb.]]>