Insulating under floor boards - 1930s Bungalow

[NickThomas]

I'm looking to insulate under a couple of rooms before I get the floors sanded.

My rough plan was to use something like Kingspan insulation boards, by jamming sections between the joists (or supporting with nails or battons). This seems like an easier solution than standard loft insulation. There is about 2 ft of crawl space.

Someone mentinoed about being careful not allow condensation to to form in the timbers, but I don't understand why this would happen and what I would need to do to avoid it happening.

So, I'm keen to find out of anyone has done this before and if it is worthwhile, and what I need to consider before giving it a bash.

Any advice in laymans terms appreciated - especially with regards potential condensation etc.

Cheers
Nick

 

[Chri5]

I did the very same thing last year.

Used 80mm Kingspan under the whole of the ground floor between 150 x 50 joists. Eleven sheets and three days of dirty, nasty work. Ours is Edwardian and the sub floor void was 3 ft.

The breathing was taken care of via five existing air bricks ( four double brick sized and one long grate) and by using 80 mm Kingspan there was a 70mm gap between floor base and top of insulation.

Every joist was slightly different in gap, some had gentle bowing and the real hassle was that it was near impossible to pre cut lengths and do a simple fit in the sub floor void.

I ended up cutting to so called measured size and then having to trim to fit when in the void (a serrated bread knife is brilliant for gentle trimming).

 

[Lower]

You avoid condensation by pushing the insulation hard up against the underside of the floorboards, not by leaving a gap.

 

[freddiemercurystwin]

by using 80 mm Kingspan there was a 70mm gap between floor base and top of insulation.

Yes as Lower says, the insulation should be hard up against the boards with no void remaining.

 

[NickThomas]

Thanks all - I'll give it a bash.

Did the insualtion make much of a difference? Is ti worth doing?

Cheers
Nick