Thread: underfloor insulation

Originally Posted by stuey

Hi , i have a wooden floor which has a few gaps in and want to put some underfloor insulation in . I have a big void under the house so plenty of space to work in . I have read about the silver concertina batts but there are too many fiddly bits to make it viable . The other option is to put normal roof batts underneath and somehow fix them to the joists . I read about using netting and a staple gun - anyone tried this and does a staple gun get into hardwood joists ok - thanks

I have seen normal roof batts under floor, the guy bought a couple of rolls of fishing line, strung that up, and then slipped the batts between the floor & fishing line....

Hi Stuey,
I'm thinking of doing a similar thing (standard batts under the floor), although I haven't decided how to go about it yet. Thought of using various materials eg. fabric, straps, etc. Let me know how you go, and if I get there before you, will give you my feedback. Cheers, Ashwood.

I have been considering insulating my 22mm yellow tongue floor as well. My current prefernce is to glue styrofoam sheeting (around 50mm) to the underside. I have also been looking at the refrigeration sheeting as there is a refrigeration mob here that sells off cuts.

The best option I have seen and I have not been able to find it since stumbling across it on Ebay is a spray on expanding foam that comes in 20 litre drums. When I worked in mining they use to use 20 litre drums of expanding foam to seal the top of exploration holes while the rigs were operating but I have never seen it as a spray on option except this once on Ebay. Has anyone else ever heard of this or know an industry where spray on expanding foam is used? It would certainly be the easiest option if the stuff will stick.

I have used a variety of methods and they all work reasonable well and in Canberra too, so quite a test.

You can use regular batts - there is specialised fixing mesh available , but you can use wire or fishing line. Fiddly job, but works fine. In my own house I have R3.5 batts in the underfloor held up with wire simply twisted zig-zag across under the joist using rows of clouts - and it made a huge difference to the feel inside the house in the rooms with timber floors. We have since carpeted some of those, but the addition of the insulation was the biggest improvement.

There are a number of companies offering expanding styrene foam - relatively costly and for a floor with good access not really justified IMHO. Great option for walls or in places where access is a problem.

The aluminium foil batts are easily compressed and damaged and much harder to obtain a good seal so OK for ceilings, but not the best for underfloor.

There are purpose designed rigid styrofoam boards for ceilings, walls and floors and it is easy to install. Thickness varies and cost goes up with thickness. There are also semi-rigid products like this one: http://www.thermotec.com.au/etherm/d...l/overview.htm

A solution that is rarely mentioned, but has worked well for me is to simply seal up the underfloor with insulation foil normally used on walls and under roofing (eg: sisalation). This can be stapled to the joists and is easy to unroll and cut. The coloured side faces the ground.

With all insulation the idea is to trap air so there is a still air gap between the two areas to be isolated - moving air is moving energy (heat). You have to make sure that you have a complete seal or you are wasting your time - but that is so for all insulation.

I have also used the foil/ fibreglass blankets usually used under under roofing material in an underfloor floor area (in a very cold climate) and again simply stapled it to the joists. Sealed over joins and gaps with aluminium A/C gaffer tape and that was very effective. Nominally R1.5 and that is fine for underfloor where heat loss is much less.

This paper is very useful and will answer many of your questions:
http://www.timber.org.au/resources/I...%20Systems.pdf

Note it is a 1.2MB file.

Hiya all, I installed concertina foil batts under my floor several weeks ago. There fairly easy to install, just staple one side up, drag it over tight to the other side, staple again, overlapping 50mm between pieces.That said I wouldn't do it again, lying on your back on 50 year old broken bottles of VB and half bricks ain't fun, my house is only 11 sq's it's still a lot to cover. I read up extensively on underfloor insulation. There needs to be gaps(not seam sealed) to allow for moisture to escape.
Previous posters seem to think that bulk insulation is a good vermin home. Someone suggested that using stiff rod to hold up the batts, slightly longer than the width of the bearers. Someone else suggested nailing up carpet underneath.
I looked into spray on foam insulation, not very eco-friendly, messy, and doesn't allow access for whatever reason. Theres lots of joints in the yellow pages that do it.

good luck