Should I fill my cavity?

Pipes & fittings need to be clean, & only a smear of flux on both.

 

Wednesbury or Yorkshire pipe for me, got given some copper pipe & fittings a few years ago, no idea what make, but it was terrible stuff, they hated solder, all ended in scrap bin.

 

Yes, good quality underlay will reduce draughts a great deal, but you also need to seal around the floor's perimeter.

If you could be bothered, you could run a bead of sealant along every floorboard groove! That is not as bad as it sounds - I did that in a previous house. I used brown frame sealant which was less that £2 a tube. I had sanded the floorboards for staining, but was worried about draughts (even tho' it was an upstairs floor) so filled every gap with the sealant. Once stained/varnished a mid-oak colour, it looked great.

Seriously, the benefits you will get from insulating the floor will be marginal. It's the coldest part of the room for the simple reason that warm air rises. Also, timber floorboards are darned good insulators. If you want to spend numerous hellish hours stuffing whatever under these boards, then go ahead. I can pretty much guarantee you that whatever you stuff under there will be simply matched by that 8mm low-dens fibreboard layer, fully sealed, on top.

Ok, when I say I've done this, I did actually fit the fibreboard layer under the boards, but that was only because I was replacing the old broken and cut boards with new ones anyway - so I had bare joists to lay the fibreboards on to, and wanted sanded timber boards as the final finish. But the hallway I did is draught-free and the floor has no 'cold' issues at all.

 

You can also run breathable membrane over the joists, seal with tape and lay insulation onto the membrane:

 

That's one minus point with using fibreboard you end up with a step, & you need to trim the doors.

 

Absolutely.

Yes, of course if the floorboards were lifted then I'd suggest adding underfloor insulation in a heartbeat.

All I'm saying is that the floor is the least important of surfaces to insulate - especially if it's timber/chipboard - and the main issue to prevent is draughts.

Since you are DIYing this and are prepared for some unpleasant graft, then great - and good luck. Don't forget to take a radio down with you to R4, and you'll have hours of top-class progs to take your mind off what you are doing.

Yes, you'd need to make the 'call' whether it was worth coping with a small step caused by the raised height of using fibreboard - it didn't happen to be an issue for me as each doorway had a wide threshold plate on it and I had carpet on one side and bare floors (with FB below) on t'other, so the respective heights were very close anyway.

But I can tell you that if you stuff the underside with insulation and don't seal off the draughts, it will be a wasted task. I can also tell you with near complete certainty that an 8mm LDFB layer covering the whole floor (either immediately above or below the floorboards) and sealed at their edges will be as effective as whatever you end stuffing in between the joists from below.

 

Stuffing in between the joists from below is easier I reckon, might need a blob of low expansion foam here & there though at the edges,were wall bows a bit.

Showing your class DA & R4, has to be Classic FM for me.

 

BBC Radio 4 or R6 Music.

No other options will be entertained...

 

Showing his age more like! lol

 

I dunno. I would certainly not use a non-breathable membrane as it will likely cause condensation and smells...

And if the use 'breathable' membrane, ain't that going to 'pass wind' too?

You don't have to feel draughts - in fact you almost certainly won't feel them coming from the floor itself. But when you open a door into that room - that's when you realise that your floor is a sieve Hundreds of tiny gaps = a draught that'll affect your room.

You don't have to use fibre boards, but I'd personally do something more than chust rely on underlay - unless you separately seal around the perimeter, under the skirtings. That might be enough.

But, we are all hoping you spend a few days underground and will post regular updates on how you're getting on...

 

Exactly, the subterranean counterpart to my loft "conversion"!!

 

If you going to do a job, do it properly. You can gain access underneath, you are doing work under there anyway so why not do it right? DA's way is ok but as you have access i would do as others have suggested. Plus, you could then also put a thin membrane on the top too! Never have a draft then!

 

Itchy coo insulation horrible stuff thank goodness it's obsolete now, bring back memories the fun we use to have with it when I was a nipper at school.