Lid for cold water storage tank

[Roger Mills]

I have a large rectangular plastic storage tank in my attic which holds the cold water to feed the (gravity fed) DHW system. [Fitted it myself some years ago - replacing a circular one - in order to make space for a loft ladder]

The tank was not supplied with a lid - but its predecessor didn't have one either - so I didn't think a lot about it.

I have recently had to replace my hot cylinder - necessitating draining the cold tank, which has accummulated all sorts of crud over the years. So I need to clean it out and fit a lid.

What material should I use for the lid? It can't be very thick because part of the tank is tucked under a purlin with only a few mm clearance. It presumably needs to be impervious to water - condsensation at any rate - so plywood, MDF, etc. probably wouldn't be much good. Maybe a thin sheet of some sort of rigid plastic? If so, what, and where can I get some without buying half an acre of the stuff? How do I hold it in place - should it have something fixed to the underside to fit inside the tank to stop it moving about? [It will obviously need a cutout to allow for the vent pipe].

What have others done in similar circumstances?

[Onetap]

Buy a new Byelaw 30 compliant tank and lid. I spent a long time looking for a lid to fit a plastic tank, but it was a complete waste of time.

You will find that the manufacturers don't make that tank anymore and you won't get a snap-tight closure with anything you might fabricate. It should also have a screened overflow and air inlet.

The proper lid should have drip mouldings adjacent to the side of the tank; without these condensation or water splashes on the underside of the lid will get under the lid.

[Frank Erskine]

I would consider heavy-gauge polyethylene sheet, which you can get from a rubber/plastics-type merchant in almost any size/gauge, and anchor it with maybe a giant bungee cord around the tank.

[John Stumbles]

Estate agent's signboard plastic. (Assuming you can't get a pukka byelaw

30 compliant lid and aren't going to do it by the book and replace the tank for one with a lid.)

[LSR]

Pond liner from a garden center might be easier to find. One advantage over a rigid lid - it's bound to sag a bit, so condensation will run towards the middle and drip back into the tank.

[Ian_m]

I made a tank lid out of two sheets of 1 1/2" (or 2 ") polystrene sheet glued together (use proper polystrene glue) wrapped on a large sheet of black 500 gauge polythene. I melted holes on the sheet and tied back using garden twine to hold it tight. This was to replace the existing lid that had been snapped by previous house owners and had been propped up out of the tank using a peice of wood that was completely black and mouldy and dripping gunge into the tank.

Also glued a block of polytyrene in underside centre of my lid to form a "drip centre". Worked fine for 10years odd till I moved.

[Lobster]

Mine just has a slab of expanded polystyrene on top.

If you want perspex/acrylic etc, when faced with a similar small-quantity requirement I recently bought a sheet about 300mm square from an e-bay dealer for a couple of quid.

David

[nightjar]

Air needs to be able to get in and out as the water level changes. Byelaw compliant lids have an insect proof air vent for that purpose.

Colin Bignell

[Adrian C]

nightjar

Insect proof is right :-) A girl at work recently had a major Ladybird infestation in her home's water tank, and millions of gritty eggs that did a good job of restricting water flow all over the house and causing other issues ....