using caivty wall batts for under gound floor insulation

[Robert Laws]

I am about to take up the chipboard floor of kitchen of my 1960s terraced house in order to replace it. While the floor is up I will have good access to the shallow void that runs under the whole of the ground floor. The floor is high enough to slide around on one's back under the joists but not to crawl. I would like to take the opportunity to install some insulation under the floor. There is additional access via a tiny trap door, but this would probably be too small for passing materials through.

As I will be lying on my back down there shoving the new insulation upwards and wedging it between the joists I want to use something with minimal lung clogging properties. Cavity wall batts seem a possibility. Polystyrene would be easy to install, but I imagine that it might cause a damp problem. The underfloor space is well ventilated but the space between the poly and the floorboards would be a moistyure trap I think.

My question is:

If I wedge cavity wall batts tightly between the joists, will they stay there or will they go limp over time and fall out?

Is there anything else I could use that would be easy to wedge and not cause damp or lung problems?

thank you for your thought,

Robert, Cambridge

[Jim Alexander]

if you are taking up the flooring this is easy, lay netting from above and fit the insulation between the joists from above resting on the netting.

Jim A

[Stuart Noble]

Celotex is very wedgeable and easy to cut, and the dust tends to be biggish chunks. It's when the joists aren't straight and/or the gap isn't consistent that the fun starts. If you can't trim it in situ, I don't fancy your chances of getting a tight fit. I found slightly overcutting and then running a handsaw between joist and foam was the best way, but sounds like that won't be an option for you. If you don't want to take the boards up, I reckon standard fibreglass is your best bet. Ghastly job but quick. I found tight fitting clothing and a mask very effective, but the eyes are the problem. Goggles that don't steam up would be a good investment if such things exist (you won't half sweat down there). The bats might be the worst of both worlds i.e. you have to cut them and the dust will probably be lighter. Personally I wouldn't bother but then I'm at the age where most things fall in that category :-)

[Phil B]

Not really answering your question I'm afraid but if you do resort to polystyrene then do keep it away from PVC cables (and water pipes?). It reacts and 'etches'the stuff away. Phil

[dennis]

That isn't usually a problem.. the plasticisers cause the polystyrene to shrink away.. once contact is broken it stops. Just don't support PVC cable with polystyrene foam.

[Robert Laws]

Thank you all for your replies on this. Polystyrene might well be the way to go, bearing in mind the possible interaction with cables.

Robert

[Robert Laws]

...The bats might be the worst of both worlds i.e. you

I'm 53 and for me this seems to be an age when I am old enough to be have become too picky to employ someone to do the job because they would not do it as well as me, but too old to have unlimited energy to do it myself, and no old enough to not bother.

R

[Andy Hall]

I know exactly what you mean. Frustrating, isn't it?

[Stuart Noble]

I find I still have the energy to do the job, but not to clear up afterwards

[Cicero]

=============================== You really should consider the possibility of taking up the floors and replacing with new. It's much less of a job than you might think and certainly easier than slithering around in the dark on your back with your arms full of insulation.

I did two of my downstairs rooms this way a couple of years ago using polystyrene slabs and new T & G timber. Total cost was less than £200-00 as far as I can remember and was done in a leisurely four days doing half a room at a time.

Cic.