underground floor heat insulation?

[Robert Laws]

I posted this earlier but it seems to have not appeared. Sorry if you get it twice.

When I take up the kitchen floor on my 1960s terraced house I will have good access to the underfloor space and i wou dlike to add some therm insulation between the joists. there is just room to move about under them on my back (but not to crawl). Once the floor is installed again i will have access to the undrefloor only via a tiny trap door. Big enough for me (houdini style) but not for passing ina materials.

I am thinking of using either cavity wall glass wool insluation or brockwool batts. I would wedge these up between the joists.

can anyone please advise me::

1) Will they stay there or will they go soft with time and fall out? I could add plastic netting underneath but it would be laborious and not too effective as the slabs are probably going to be thinner than the depth of the joists.

2) Can I use anything that is less unpleasant for my lungs? I am going to be lying on my back shoving these things into the space just above me so it will not be pleasant. Is polystyrene an option? I guess not because it is not permeable to water vapour. Perhaps you can get perforated polystyrene?

3) I think that the insulation designed for putting between roof rafters would be no good because it incorporates a vapour barrier, which is not required in my under floor situation. Am I right?

Thanks you for your help,

Robert

[Jonathan Pearson]

It appeared on my system at 11:26 Jon

[Tony Williams]

What if you were to use netting that is fine enough to be stapled to the top of the joists.

Staple the netting along the top of the first joist.

Lift the netting up over the second joist to form a trough.

Drop the insulation slab into the trough.

Tighten the netting until the top of the slab is level with the top of the joists.

Staple the netting along the top of the second joist.

Keep going.

All top work.

[John Stumbles]

I did this using cheap garden netting and rockwool. AFAIK it's still there, but since there's no access to the underfloor area I've no way of knowing!

I also screwed Screwfix' builders' band across the top of the joists and cable-tied 15mm Hep20 to it, run in loops up and down between the joists, to give primitive underfloor heating. It works OK but the heat's a bit uneven. The floor is wood with ceramic tiles on top.

[The Natural Philosopher]

I did.

If you are taking up the floor its a piece of cake to do the job PROPERLY.

Get some celotex - I recommend 50mm - and drive in nails - or nail battens - 50mm down from the floor base. To support the slabs

Cut the celotex and wedge it in. Sharp serrated kitchen knife is pretty good.

Tape over the joists with foil tape.

[Robert Laws]

Sorry, did not express myself clearly enough. The kitchen floor is about 10 sq m. I want to add insulation under the existing floor of the rest of the 50 sq m ground floor by crawling underneath in the

40cm high space. I don't want to take up the rest of the floor. thye kitchen floor coming up gives me the ability to get materials down into the under floor space. R

[The Natural Philosopher]

Well i'd still whack up celotex. Jam it between the joists and use nails to hold..afterwards you can go around with a foam gun if there are major gaps.

Then use a waterproof membrane above the basic floor before laying finished floor - if using vinyl, or tiles, that's good enough by itself.

[chris French]

Rather you than me, having worked under floors, 40 cm isn't much space at all.

Have you checked under there yet? You will quite probably find that you can't easily get access to all the under floor space anyway as there will probably be walls in the way - Weight bearing walls will continue down to the foundations, and there may well be sleeper walls - low walls buuilt under the floor midway across a room to support the floor joists