Under floor insulation?

[Imintheshed]

Hi all,
We live in a 1930's semi with a crawl space that seems to be on first name terms with the North wind. Although the floorboards have a layer of insulation and then some engineered wooden flooring on top, it still feels flipping freezing in mid winter.

I've tried blocking the air vents up (and yes, I'm aware that the vents are there for a reason!) but that still leaves the block of frozen air.

There is no way of accessing the crawl space to retro-fit thermal insulation blocks between the joists without chain-sawing my way in.......and thats just going to be noisy and fill the house with 2-stroke fumes.

I'm inspired by the concept of cavity wall insulation, is there something that I can 'pump' in to the crawl space? I'm thinking polystyrene balls (if I can spell them) or those packing chips or........

Any views?

[guydewdney]

<AOL moment>
me too
</aol>

Can't the floor be lifted? Is it nailed down? I have a suspended wooden floor, under which is stapled some chicken wire, and an insulting amount of glassfibre insulation (1" maybe?). I wondered about some blown in insulation - as per lofts, cavity walls etc - but I have no further help. My kitchen floor is tiled, so I cant lift the floor - but I can in the living room.

Guy

[Iain]

Hi
I have put in an access under the stairs for my crawl space, I have maple floor fitted straight onto the joists so didn't want to lift it.. I fitted 100mm rockwool between the joists held in with 50mm kingspan . All fitted from underneath. A pain to do but a fantastic difference. No drafts and a lovely warm floor. Just done the same at the Mother in laws and again a fantastic improvement. Is there anywhere you can make an access, even a temporary one?
Iain

[biff]

well first thing is,, the crawl space could be 4ft and that would take a massive amount of insulation before it would get up to the floor,then it will settle and leave a space and you will be back to square one,pick a spot to access underneath,design a good trapdoor,i would suggest the centre of the house,next to a wall. you will probely find your passage restricted from room to room underneath in the crawlspace so you can break a small hole in an appropiate place to give proper access.
        fiberglass encases in foil would be your best bet, or 4" poly board in 8x4 sheets cut down to fit and jammed up between the joists,or both,using the poly to hold up the fiberglass. you will have to wear a mask and a good quality boilersuit,
                                                                       biff

[EccentricAnomaly]

Obligatory reminder of the need to think about condensation.

Having seen my father go through my bedroom floor when I was about 7 or 8 it's something I'd pay attention to. In that case it was a water leak resulting in a small stream across the earth under the floor but, with forty-odd year's hindsight, I do wonder if there was perhaps also a problem with the ventilation to cause rot in the wood which wasn't in direct contact with the water.

Kingspan under the joists seems, to me, like something to be treated with great deal of caution. Some sort of netting to hold the insulation in place is a common solution but if you do want solid insulation under the joists then I wonder if something a bit more breathable like wood fibre board wouldn't be safer.

[Imintheshed]

Hmmm......thanks for the thoughts....

I really dont want to lift the flooring; it is T&G and glued for good measure and will just end up splitting.

I suppose that I could MAYBE gain access under the stairs, crawl through the electric cabling and then break a hole through the brickwork into the crawlspace under the living room (its already sounding more and more like the Great Escape). One problem with this though is that the house, which is completely open plan (living room to dining room to kitchen), all with the same flooring running through it, is built on a gradient and I know for a fact that the gap under the dining room isnt going to be accessible without getting the wife's permission to send our 5 year old in.
Another problem is going to be getting the insulating materials down the hatch and into place under the floor; it would certainly rule out anything big (like a roll of rockwool) or solid (like the Kingspan).

[Iain]

Hi
I went down and measured all the sections then cut the sections of rockwool and kingspan in the house and just passed each piece down as required.Easy with 2 people. The kingspan was used to purely hold the rockwool in place and were a "non sealed" fit between the joists. Just an easy means to hold the rockwool in place. I held the king span in place using lots of offcuts of 2x1 4" long. Just screwed to the bottom of each joist, the kingspan just sits on each piece. The joists are still able to breath.
Iain

[Brandon]

170mm rockwool and breathable frame felt here (and an apprentice with want of anything more useful to do one morning!)

[knighty]

isnt going to be accessible without getting the wife's permission to send our 5 year old in.

when I was 5.... I'd have been down that hole quick as a flash before anyone had time to think about permission !!!

[biff]

aye aye knighty,
           like me, you would be looking for buried treasure or the odd florin or half crown which slipped through the cracks in the floorboards.
                                       biff

[Jonathan]

How about
a, block all the outside air vents/bricks.
b, cut a hole in the floor indoors somewhere and set a fan up to blow air constantly downwards into the void.
c, drill some small ventilation holes in the floor far from the fan, and beneath radiators so the returning air gets warmed again.

After a while, the void will warm up (or wont be so cold), and you stop the condensation problem?

[skyewright]

...already sounding more and more like the Great Escape. One problem with this though is that the house, which is completely open plan (living room to dining room to kitchen), all with the same flooring running through it, is built on a gradient and I know for a fact that the gap under the dining room isnt going to be accessible without getting the wife's permission to send our 5 year old in.

I did our underfloor last year. In places there was only around 7" between joist & the earth! See attached.

As I really didn't fancy working with fibre/wool down there and I've had good results from using it in other places I adapted Airtec Double (a foil-bubblewrap-foil sandwich) for the purpose. The insulation goes halfway up the joist, across the gap then down to the bottom of the next joist, i.e. an upside down U shape. The airtec comes on rolls 1m wide. As the joists are regularly spaced I could pre-cut a number of sheets and feed them through the tap door before each session down the hole. Where there are joins I overlapped by ~100mm. Where it was particularly tight I found that spreading out bits of cardboard boxes on the floor of crawl space (just bare earth) made it easier to slide about (and less messy).
Once that was done I underdrew the whole thing by stapling landscape fabric across the joists. Over most of the area the cross section is now floor, air gap, Airtec Double, air gap, breatheable fabric, crawl space.

The insulation material itself is impermeable, but should be able to 'breathe' via the overlaps. In the event of a serious spillage 'above' the upside down U should allow water to drain through.

It has had a very positive effect this winter.  

[Imintheshed]

Thanks David,
If I'm going to commit to re-living my pot-holing youth then the Airtech looks a lot more attractive than wrestling with fibre-glass.
I usually embark on these sorts of projects when Mrs C takes the little man back to her native Holland......under the circumstances I might just ensure that she is around to feed me bits of insulation, staples and, worse case, maybe soup through a hosepipe!
Cheers
Rich

[mespilus]

worse case, maybe soup through a hosepipe!
Cheers
Rich

Best make certain it's 'Cream of....' rather than 'Chunky...'.