Using Wall Insulation for Underfloor Insulation

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  Switchblade88 on 22/05/2021 - 13:55

  Likely doesn't matter. As long as you have a good way to affix it underneath so it doesn't sag, you'll be good

  • 

    itsTricky83 on 22/05/2021 - 14:17

    Thanks Switchblade

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  frostface on 22/05/2021 - 14:03

  +1

  Not going to matter, there is no difference in thermal properties between R2.5 wall and R2.5 floor/ceiling, and both are easy enough to install - but don't rely on friction alone as it will eventually drop. R2.5 wall is likely to be thinner and denser, which has better acoustic properties, that's the only real difference. Likely he pushed it as it's a more expensive product.

  • 

    itsTricky83 on 22/05/2021 - 14:17

    Thanks frostface

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  bloom on 22/05/2021 - 14:52

  +2

  Getting the right width is key to making installation easy, too narrow it just falls out, too thick it keeps popping out. As above make sure you strap the joists

  • 

    itsTricky83 on 22/05/2021 - 18:27

    Thanks Bloom.

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  resisting the urge on 22/05/2021 - 16:40

  +1

  Best way is to put the bulk between the joists, then add a layer of 25mm polystyrene, then strap (or strip, *see below).

  The reduction in thermal flow (increased R value) is far better too, so makes it worth the extra expense. Also, ' the white ceiling' really improves visibility under the living space for those doing the hard work :-)

  What I do is cut lots of pine strips (30x10) to 250mm long, and nail or screw them into the joists at 1m spacings, before beginning to place the insulation. Then you begin placing each piece, so once in, you simply twist the pine strip 90 degrees and it holds the insulation on both sides of the nail.

  A big plus is it makes placing the insulation really fast (saving your back) and in future i t is really fast to remove and replace any piece without tools. Really handy for when you need to access plumbing or electricals.

  Tip: Have a permanent pen in your pocket, so you can note the services above the insulation, as you go, on the polystyrene, to make finding things later simple when maintenance requires it.

  • 

    itsTricky83 on 22/05/2021 - 18:34

    Thanks Urge!
    Good tips. We might go all out and add the extra styrofoam eventually. I do really like the clean look of the styrofoam. A mate did just that a few years ago.

    Half of the underfloor area is an old garage which a dog's breakfast of different width joists. We just got that done this arvo and already feel a huge difference to the warmth of the house. The wiring and plumbing is really crap in this house but therefore it is also easy to identify even with the insulation in place.

    Thinking further about the styofoam, I might add it to the Garage area to create a clean look. But first I'll need to sort out a pretty unprofessional wiring job. Of which half is old-school 2wire black wiring (no ground wire).

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  mini_wombat on 10/06/2021 - 13:52

  +1

  I recently upgraded our ceiling insulation and it made such a massive difference. Used some R4 Earthwool from Bunnings … was the most economic (compared to the R6 which is substantially more expensive … I rather put two R4 on top of each other to reach R8 and also cover the joists.). One important thing is to also seal the possible draft spots up and worry covering electricity cables (have sparky check it!).

  No I also think about insulating the floorboards - there is not much space. I steered away from the styrofoam (as it's hard to install and you can't touch any electricity wires - as it destroys the plastic insulation on the cables. Earthwool from Bunnings needs to be strapped in and might start sagging after some time. I am now thinking of Polyester insulation - easy to staple in with an electric staple gun and similar price to the Earthwool Underfloor insulation. I read that rodents like mice and rats don't like that stuff - so that is a plus. Ideally would be foam spray insulation which also would stop all drafts and covers the joists - but I guess this not cheap and you can't DIY.

  Ah well … I guess anything is better than nothing.

  @Tricky83 just make sure you don't have the normal wall insulation … this will sag over time as it is not that stable. The HD (High Density) or SHD (Super High Density) Earthwool would be fine … just misses the windshield. But I think there is no normal one in R2.5 as I only found a R2.0.
  I guess you have this: https://www.bunnings.com.au/earthwool-r2-5-hd-90mm-x-430mm-x…

  Polyester I want to use: https://ecomasterstore.com.au/collections/underfloor-insulat…

  • 

    itsTricky83 on 10/06/2021 - 21:45

    Thanks Mini_Wombat,
    The sag over time is a concern, but we've had to go with it because it was already purchased without me being consulted.
    We've almost finished installing it. The rest will be done this weekend.
    I'll probably need to come back and strap it up in a few months but for now it's holding on quite well.
    Good to hear that rodents aren't huge fans of it.. makes sense in a way, what animal would enjoy eating shards of glass.
    After installing it to all sorts of difficult corners of the house, I really do give credit to anyone who installs insulation as a full time job… Faaaarq that!

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  Shamblowie on 09/05/2024 - 08:08

  I know this is an old thread, just looking at insulation underfloor as well and comparing the windshield underfloor with the sound shield wall insulation, someone at Bunnings said the windshield will stop condensation, mildew / moisture from gathering from being exposed to it under the house and then forming mould. Did you end up installing the wall insulation under the floor and if so have you noticed any moisture gathering on the wool?