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Heating and cooling: Insulating under suspended floor

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  1.  
    • CommentAuthoromehegan
    • CommentTimeAug 6th 2021
     
    As mentioned in a previous thread, I am a relatively new owner of an 1880s Victorian house in Melbourne, Australia, which currently has no insulation in it at all. The walls of the house are solid brick, and it has suspended timber floors over bare soil ground, with passive air vents around the perimeter. In the process of getting our kitchen renovated, we unexpectedly find ourselves pulling up the floor in the kitchen/living/dining area of the house to replace old stumps/footings below.

    As a result, there might be an opportunity to install insulation below these floors, but there are some constraints. First, there is only about 30-40cm clearance below the joists, so solid board insulation below the joists can't be installed. It would have to be rockwool batts between them, held in with strapping or similar that can be installed from above. Second, I doubt I can get a pro installer in in time to do this without hugely impacting the rest of our remodel timeline - the old kitchen was removed 4 weeks ago and we still have another 2-3 weeks to go before the other work is done. I can't really add another couple of weeks to wait for an insulation installer. Third, I am wondering if it's necessary to install some kind of vapor barrier in addition to the insulation batts - I have seen places that recommend a plastic membrane both above and below the batts. Is that best practice?

    I think to do this at all, it's going to have to be something simple that I can DIY in a short time. Lowest winter temps here probably average about 12C during the day, 5C overnight - rarely dips close to zero. So I almost wonder if it isn't really worth trying to insulate the floor, given the rest of my constraints. Interested to hear any thoughts from the group.
    • CommentAuthorEd Davies
    • CommentTimeAug 6th 2021
     
    Posted By: omeheganI have seen places that recommend a plastic membrane both above and below the batts. Is that best practice?
    No. Maybe above or below depending on the circumstances but I don't think it would ever make sense to do both and would likely be quite dangerous as condensed water could easily accumulate between them with no way to dry out.

    In the UK the usual thing would be to either not have a vapour barrier or to place it above the insulation batts with the idea that any water could dry out downwards assuming that the space below is reasonably well ventilated or at least that the ground is dry enough to absorb vapour. If the ground is wet for much of the year things are more interesting.

    In places like Washington DC, where air conditioning is common and outdoor humidity is high, the vapour drive is the opposite to the UK, from outside to in, so any vapour barrier would go on the outside.

    My guess would be that Melbourne would be similar to the south west UK but a bit drier in which case the vapour barrier would go on the inside but others likely know better.
    • CommentAuthorSimonD
    • CommentTimeAug 7th 2021
     
    To keep it simple you can just run some type of netting or a breather membrane over the joists, stapling in place at the bottom edge of the joist to span across to the next. Then install insulation of your choice, like Rockwool. With the floor, if you replace the existing floor with an osb subfloor, this will double as a suitable vapour barrier. Then just make sure you seal around the perimeter at the wall and ensure the osb boards are nicely glued.

    It's all a fairly simple diy job if not entirely enjoyable.

    Have fun.
  4.  
    The sub-floor ventilation wants to be *excellent*, and proper cross-ventilation. Corner-to corner (and some intermediates if it's a wide plan) as well as straight-across. If it's not excellent you may get 'stagnant' areas where condensation forms. If there are any cross-walls in the way, you will have to cut air-vents in them.
    •  
      CommentAuthordjh
    • CommentTimeAug 7th 2021
     
    Posted By: Nick ParsonsThe sub-floor ventilation wants to be *excellent*, and proper cross-ventilation.

    Otherwise there may be the possibility of using Tom's much-quoted scheme for converting to a fully-fiilled insulated and unventilated space. Sorry don't know a link to the previous discussions.
  6.  
    •  
      CommentAuthordjh
    • CommentTimeAug 8th 2021
     
    Tom's suggestion doesn't involve a solid floor, just filling the void with EPS beads, as briefly mentioned in the fourth of your links.
  8.  
    Thanks djh - yes, I'd forgotten about that. The problem may be that, allegedly, some BCOs are not happy with the full-fill method below the exg susp floor. Solid floor, whether 'conventionally' laid up, or with space taken up with thick EPS boards, seems more likely to be acceptable in any BCO's view.
    • CommentAuthorEd Davies
    • CommentTimeAug 8th 2021
     
    Posted By: Nick Parsons…some BCOs are not happy…
    As an aside, it'd be interesting to hear how Australian building control works for this sort of thing. Do they get involved, etc.
    • CommentAuthoromehegan
    • CommentTimeAug 9th 2021
     
    I think I have made the somewhat tough decision to give this a miss. Time is not on my side, but on top of that the builder pointed out that the hydronic heating pipes which criss cross this area to connect up several radiators are themselves a source of some heat under the floor. Of course it's not completely ideal, but he felt that the additional benefit of insulation in this specific situation may not be worth the effort. I'll be putting down 28mm thick tongue and groove floorboards directly on the joists, so at least there will be no gaps between them.
  11.  
    Posted By: omeheganTime is not on my side, but on top of that the builder pointed out that the hydronic heating pipes which criss cross this area to connect up several radiators are themselves a source of some heat under the floor.

    I trust these pipes are insulated given that your under floor is ventilated to the outside.
    • CommentAuthorjms452
    • CommentTimeAug 9th 2021
     
    Posted By: omeheganthe builder pointed out that the hydronic heating pipes which criss cross this area to connect up several radiators are themselves a source of some heat under the floor. Of course it's not completely ideal, but he felt that the additional benefit of insulation in this specific situation may not be worth the effort


    Take your builder's views on 'how you do it' into account but 'what you do' is up to you.

    Your climate sounds relatively mild so full full etc is overkill (in my opinion) but insulating the heating pipes and putting circa 100mm insulation between the joists is a no brainer if the floor boards are coming up.

    Suggest asking your builder 'If I wanted to put some insulation down while the floor boards are up what would you recommend' and reporting back.
    • CommentAuthoromehegan
    • CommentTimeAug 9th 2021
     
    <blockquote><cite>Posted By: Peter_in_Hungary</cite>
    I trust these pipes are insulated given that your under floor is ventilated to the outside.</blockquote>

    They are, but the insulation is not in great condition now at 30-40 years old. Another thing I don't really have time to improve at the moment. Doesn't help that we are back in lockdown here, so the home improvement and other hardware/supply type shops are only open to tradespeople, who are all up to their eyeballs in work. I can't even DIY stuff effectively right now.
  14.  
    Posted By: omeheganThey are, but the insulation is not in great condition now at 30-40 years old. Another thing I don't really have time to improve at the moment.

    If you are going to put new floor boards down when would you improve the pipe insulation that you say is in poor condition? I suspect never - and it will only get worse.

    Posted By: omeheganDoesn't help that we are back in lockdown here, so the home improvement and other hardware/supply type shops are only open to tradespeople, who are all up to their eyeballs in work. I can't even DIY stuff effectively right now.

    Do online shops still operate and are you able to order from them. Once you have the floor board up it won't take much extra time to replace the insulation with modern tube type insulation (or even add on top of existing if the existing is wrapped felt insulation which can be a pain to remove).

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