Insulating under cold water tank?

Section62

ThisIsWeird said:

Section62 said:

Personally I'd use my skills to arrange the insulation - possibly with the gold plating of some extra chipboard to box in the void between tank support platform and the ceiling below - such that as much heat as possible is directed up to the tank, and as little as possible is lost into the loft.  It should be achievable with a little ingenuity.

I'd suggested something along these lines earlier on, but simply using draped insulation to form this 'heat tube' from the loft floor, but now realise it might actually not be a good idea at all.  If some insulation is removed from the loft floor under the CWS in order to allow this bit of heat to reach the CWS, and this 'house heat' is contained - directed - to the CWS via an insulated channel which won't be thoroughly ventilated to the rest of the loft (and it would be pointless if it were), then I suspect moisture coming up from the house along with this warmth will hit what will be for the most part the coldest surface in the loft - the bottom of the CWS tank - so will condense out. And, not being ventilated away, this will likely drip on to the ceiling under the CWS.

Two things here - firstly if we are talking about water vapour coming up from the room below through the plasterboard then there is no particular reason why it wouldn't continue through the mineral wool insulation and go elsewhere - mineral wool is more permeable than plasterboard.  Not forgetting that vapour check plasterboard has been in use for a long time now, and if that has been used then condensation from this source shouldn't be an issue.

Secondly, the underside of the platform supporting the tank is unlikely to be the coldest surface in the loft in the winter months - for the same reasons you set out in the rest of your post.  Water has a fairly high specific heat capacity and with a moderately large volume of water in an insulated tank, it will take some time for the (say) ~8C water to lose the heat energy contained within it.  Some of that heat energy will be lost down into the support platform.  Combine that with some warmth coming up from the ceiling below and there is a reasonable chance of keeping that surface relatively toasty-warm compared to other surfaces in the loft which are more exposed or have lower specific heat capacities, and therefore cool down more rapidly as the temperature outside drops.

This isn't done because it is necessary to stop the (whole) tank contents freezing, it is just to keep the area around the tank a bit warmer than the rest of the loft, in part to control condensation.  In some areas (and with council properties in particular) it was fairly common to construct a block wall around the cold water tank after it had been installed and top it off with a 2" strawboard cover - the 'deluxe' insulation option, but making it a real PITB to do any maintenance work on the tank.

cerebus

So to answer the OPs question and I think we're all in agreement here, keep the insulation as is and enjoy your house 

Section62

cerebus said:

So to answer the OPs question and I think we're all in agreement here, keep the insulation as is and enjoy your house 

Not sure how you've come to that conclusion.

Standard practice is not to insulate under water storage tanks in lofts, except in some special cases where the loft itself is insulated to make it a warm space. Several posters have confirmed the OP's initial view regarding this standard practice being correct.

Nobody has presented a compelling argument why the OP should depart from standard practice, although what they choose to do is ultimately up to them.

Please don't mislead forum members by claiming "we're all in agreement" with the view you've expressed, when that clearly isn't the case.

ThisIsWeird

Section62 said:

Two things here - firstly if we are talking about water vapour coming up from the room below through the plasterboard then there is no particular reason why it wouldn't continue through the mineral wool insulation and go elsewhere - mineral wool is more permeable than plasterboard.  Not forgetting that vapour check plasterboard has been in use for a long time now, and if that has been used then condensation from this source shouldn't be an issue.

Secondly, the underside of the platform supporting the tank is unlikely to be the coldest surface in the loft in the winter months - for the same reasons you set out in the rest of your post.  Water has a fairly high specific heat capacity and with a moderately large volume of water in an insulated tank, it will take some time for the (say) ~8C water to lose the heat energy contained within it.  Some of that heat energy will be lost down into the support platform.  Combine that with some warmth coming up from the ceiling below and there is a reasonable chance of keeping that surface relatively toasty-warm compared to other surfaces in the loft which are more exposed or have lower specific heat capacities, and therefore cool down more rapidly as the temperature outside drops.

This isn't done because it is necessary to stop the (whole) tank contents freezing, it is just to keep the area around the tank a bit warmer than the rest of the loft, in part to control condensation.  In some areas (and with council properties in particular) it was fairly common to construct a block wall around the cold water tank after it had been installed and top it off with a 2" strawboard cover - the 'deluxe' insulation option, but making it a real PITB to do any maintenance work on the tank.

Yes, I was thinking of the water vapour that percolates up from the house below - I presume that's what causes most condensation problems found in lofts?

I still think there could be issues if a heat tunnel is formed. You mentioned this tunnel could perhaps be chipboarded as well as insulated, and that would reduce the ventilation to that area pretty comprehensively, I'd have thought? So a combination of a steady diffusion of warm, moist air trickling up from the house below, being trapped inside an insulated box, and in permanent contact with a surface which will be the coldest for large parts of the year.

Interesting one - and I just don't know what would happen in practice.

Anyhoo, my personal recommendation to anyone concerned about a freezing CWS would be to insulate it to current by-laws, and then build a PIR box snugly around it if paranoi... er, still concerned.

It just is not going to freeze. It ain't. I'll bet a £iver on it... :-)

cerebus

Section62 said:

cerebus said:

So to answer the OPs question and I think we're all in agreement here, keep the insulation as is and enjoy your house 

Not sure how you've come to that conclusion.

Standard practice is not to insulate under water storage tanks in lofts, except in some special cases where the loft itself is insulated to make it a warm space. Several posters have confirmed the OP's initial view regarding this standard practice being correct.

Nobody has presented a compelling argument why the OP should depart from standard practice, although what they choose to do is ultimately up to them.

Please don't mislead forum members by claiming "we're all in agreement" with the view you've expressed, when that clearly isn't the case.

Please don't mis quote me and cherry pick what I said

I said "I think we're all in agreement" 

I am merely trying to extend the debate lots of interesting views here

It is you who is being misleading