Most effective insulation under carpet – above suspended vented wooden floor

Discussion in 'Builders' Talk' started by MarcusHalberstram, Apr 30, 2022.

  1. MarcusHalberstram

    MarcusHalberstram New Member

    My living room is on ground floor. It has a suspended wooden floor over a large vented cavity (several feet deep). It gets pretty cold in winter. I want to get carpet in this room; both for comfort and to increase the warmth/insulation in the colder months. I’m aware that doing under-floor insulation would be the best way to insulate this room, but it’s a large room and this would be expensive and disruptive so I’m unlikely to go down this path at present given my budget.

    I want to get the most insulation I can from above-(floor)board insulation/underlay/carpet.

    I came across this ‘Eco-Tech floor foam insulation’ stuff online which seemed like a silver bullet for my situation; as a solution to increase insulation above floorboards (but below carpet underlay):

    https://www.ecohome-insulation.com/product/ecotec-floor-foam/

    But delving a little deeper I’ve begun to think it may just be snakeoil. I can’t find much in the way of genuine trade advice on its effectiveness and or suitability for this situation. I’m also concerned it would effectively form a waterproof membrane above the floorboards which may ultimately lead to issues of mould/damp under the underlay. Any experience/trade-level advice most welcome!

    Whether or not I the above, I’ll be looking at filling gaps in floorboard best I can the getting the max tog carpet/underlay combo. The best rated underlay I seemed to find was Wilsons Plushwalk 12mm:

    https://www.carpet-underlay-shop.co...ushwalk-12mm-carpet-underlay-from-3-05-per-m2

    …but this seems to have a damp proof membrane (DPM) built in – and again I’m concerned that this could cause issues like the above given the nature of the floor underneath (suspended wooden floorboards over vented cavity). Is this a valid concern? Would I be better with a non-DPM underlay?

    Any advice on any of the above – or alternative solutions to getting the best insulation I can from above-board (literally!) work in this room would be most welcome!

    Many thanks
     
  2. Gary Harrison

    Gary Harrison New Member

    I am in a similar situation to yourself and was seeking similar advice. I was considering using a plastic dpm sheet, taped around the edges to stop cold draughts from our ventilated suspended timber floor. I was also worried about damp. I will be laying laminate flooring over an insulated underlay. Hopefully, that will stop any moisture in the air condensing on a cold surface (the laminate). You can also get membranes that are 'vapour open' which I think would help stop the cold draughts but still allow the materials to breathe. All guesswork though and it would be good to get others opinions/advice
     
  3. MRY

    MRY Screwfix Select

    If it's got than much of a space under the floor, can't you insulate it from under?

    I had a quick look at ‘Eco-Tech floor foam insulation’ but I can't find any heat specifications, so I would be suspicious. You could always call them or another sales outlet and ask.
     
  4. Resmond

    Resmond Active Member

    At 4mm that ecotech stuff wont be much better than any other laminate style foam underlay, seems a bit pricey for what it is.. the real job would be to insulate between the floor joists then put the boards back and underlaycapet
     
  5. MarcusHalberstram

    MarcusHalberstram New Member

    Thanks for your posts. As I said in opening - I’m not really up for doing insulation under the boards (lifting them etc). It might be the ‘real job’ but prob at least a £2K job and disruptive. And going from under is not option - there’s no access under the void.
     
  6. MarcusHalberstram

    MarcusHalberstram New Member

    But is it safe to use without creating damp issues in this case?
     
  7. Resmond

    Resmond Active Member

    This is actually an area of contention.
    Some say you shouldn’t add a vapour barrier above for exactly this reason however to lay a solid or engineered floor on the ground floor it’s recommended to use a membrane/bitumen paper to stop moisture issues with the floor and many floors are fitted that way…
    So tbh if i was gonna fit it i’d go with a non vapour barrier underlay or more likely just save the money and spend more on the carpet underlay.
    That said if there’s no current damp issues below with adequate underfloor ventilation it may be fine.. another workaround I’ve heard of is using a spiked carpet seaming roller to add perforations, whether that works or not can’t say
     
  8. MRY

    MRY Screwfix Select

    You could lift "some" boards to get access. How big is it? (No! The *room*!)? If you're worried about condensation, but want to cure draughts, put down hardboard and make sure the edges are sealed under the good underlay, it'll be vapour-permeable but draughtproof.
     
  9. MarcusHalberstram

    MarcusHalberstram New Member

    But a good underlay WITHOUT a DPM?
     
  10. MRY

    MRY Screwfix Select

    Hardboard is not a DPM.
     
  11. just pumps

    just pumps Screwfix Select

    I noticed the underlay in the second link is 12mm thick so regarding skirting boards etc how would it look in the room with carpet on top. ie would doors need triming down to open?
     

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