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Insulating raised water storage tanks in an attic

  • 25-11-2020 11:52am
    #1
    jack of all
    Registered Users, Registered Users 2 Posts: 2,376 ✭✭✭


    Our house is 20 years old with a standard trussed roof attic void, with approx. 250- 300mm overall thickness of mineral wool insulation, a combination of 2 layers laid between and over the ceiling joists. The cold water storage tank and feed and expansion tank are located on a raised base, approx. 1m above the ceiling rafters. These tanks are insulated on the top and sides with mineral wool in plastic sleeves, snugly fitted. All pipes are lagged, including gate valves, bends and unions, all taped etc. The ceiling area under the tanks was never insulated, which was common practice at the time. This is bothering me as it is obviously a serious source of heat loss, one which I'd like to address now.

    Now to my question- current building regulations state that in the case of raised tanks that "the ceiling should be insulated normally and the tank insulated separately". If I were to do this (say bond polystyrene board to the underside of the timber base and insulate the ceiling below) do I not run the risk of the tank freezing in a prolonged cold spell. It is not practicable to continue the ceiling insulation up to the tanks- the tank base is a stud framework, with bracing etc, resting on 9x2" bearers etc. Has anyone insulated their raised tanks as per TGD Part L 2019 and how did it work out?


Comments

  • #2
    listermint
    Registered Users, Registered Users 2 Posts: 34,106 ✭✭✭✭listermint


    Two things. Our climate rarely has the temps required to freeze a tank like that especially if it's insulated as you have it and the water is continuously in use.

    But also you could frame out the bottomg of the box it site on in insulation on all sides to bring the heat up to the underneath of the box.


    Finally you might be over thinking the scale of the heat loss from this. Airtightness is more important for this scenario. You'd be better served making sure attic doors are sealed fully and airgaps in plasterboard etc are not causing problems.

    I'd argue insulating below the tank will give you little to no gain or benefits.


  • #3
    jack of all
    Registered Users, Registered Users 2 Posts: 2,376 ✭✭✭jack of all


    Thanks for your reply listermint; I understand air leakage is probably a more serious consideration, so to that end I have sealed all cable and pipe penetrations with silicone or butyl sealant and the (sprung) trap door is fitted with a compressible seal. The ceiling plasterboard is foilbacked and where I did find the foil damaged (through over-large service holes etc) I repaired the missing foil with self adhesive foil tape. I think I've gone as far as I reasonably can with airtightness.

    It's not really practical to box out the sides in insulation as you suggest, it's a very tight framework of timbers with too many obstructions etc. I think you are probably right in suggesting that insulating the underside is of little benefit, as it sits on 19mm T&G flooring, so heat loss/ gain through this will be negligible. My only worry was if the tank was unused for a period during winter (say the house is unoccupied for a few days in a prolonged cold spell) would no water usage lead to ice formation. I am probably overthinking this!


  • #4
    listermint
    Registered Users, Registered Users 2 Posts: 34,106 ✭✭✭✭listermint


    jack of all wrote: »
    Thanks for your reply listermint; I understand air leakage is probably a more serious consideration, so to that end I have sealed all cable and pipe penetrations with silicone or butyl sealant and the (sprung) trap door is fitted with a compressible seal. The ceiling plasterboard is foilbacked and where I did find the foil damaged (through over-large service holes etc) I repaired the missing foil with self adhesive foil tape. I think I've gone as far as I reasonably can with airtightness.

    It's not really practical to box out the sides in insulation as you suggest, it's a very tight framework of timbers with too many obstructions etc. I think you are probably right in suggesting that insulating the underside is of little benefit, as it sits on 19mm T&G flooring, so heat loss/ gain through this will be negligible. My only worry was if the tank was unused for a period during winter (say the house is unoccupied for a few days in a prolonged cold spell) would no water usage lead to ice formation. I am probably overthinking this!

    I think youve done an excellent job so far tbh. And it sounds pretty much enough. Have a beer! :)


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