Posted By: costley111Crawlspace itself is quite deep - about 1m, and for that, EPS Beads doesn't seem to be an option.

You mean on cost grounds?

There are air bricks, though each rooms crawlspace seems confined to the room itself, partitioned off from others with brick etc, not sure if that is a thing - unsure how air can flow under if it is a single entry point at the 1 air brick per rooms crawlspace.

Do the joists rest on the brick? Are the walls above supported on the brick walls underfloor? Is everything sealed or are there gaps between the brickwork and joists and if so, how big?

The floor joists are quite short, height wise, only 9cm - so the question is, if using the insulation roll/netting method - is it fine to completely cover the joist itself with the insulation... if using 200mm insulation roll for example, then there would be approx 110mm below the level of the bottom of the joist - much like insulation in an attic - though upside down.

Those joists are not very deep. Does the floor feel solid? Regardless, it will be fine to completely enclose the joists in insulation and for exactly the same reason as for ceiling joists - it keeps them warmer than they were.

in regards to vapor control etc, in this situation, what would you all suggest?

I would definitely use vapour-open insulation such as rockwool and given you don't want to lift the floorboards, I'm tempted to suggest no vapour barrier. You do want an airtightness barrier though, so a membrane of some kind somewhere - perhaps underneath the insulation? Possibly you could consider a liquid vapour barrier sprayed on the underside of the floorboards?

It would be fine to do 200mm of underslumg insulation, I would do two layers of 100mm

Vapour barrier on warn side of the insulation, can double as air barrier too.

You mean on cost grounds?

100%

Do the joists rest on the brick? Are the walls above supported on the brick walls underfloor? Is everything sealed or are there gaps between the brickwork and joists and if so, how big?

The joists rest on the brick yes. And for the walls also yes. There are gaps, can't recall right now how big, but this could be filled with rockwool, and expanding foam where neccesary?

Those joists are not very deep. Does the floor feel solid? Regardless, it will be fine to completely enclose the joists in insulation and for exactly the same reason as for ceiling joists - it keeps them warmer than they were.

Floor feels solid alright. That's good to hear, per your next point, I may go 100mm rockwool between joists, and 100mm again crossed over.

I would definitely use vapour-open insulation such as rockwool and given you don't want to lift the floorboards, I'm tempted to suggest no vapour barrier. You do want an airtightness barrier though, so a membrane of some kind somewhere - perhaps underneath the insulation? Possibly you could consider a liquid vapour barrier sprayed on the underside of the floorboards?

We're getting carpet in 3x of the rooms, whereas another 3 will be laminate. Would an airtight barrier above the floorboards but beneath underlay be wise? And not a vapour barrier?

I'm using breathable roofing membrane on the outside face of the insulation. I was worried about wind washing and condensation, so a vapour barrier scared me - but I am not an expert on this.
One room done about 4 years ago and seems to be working well, no signs of any issues when I looked the other day. Am doing rest of ground floor currently

No need for ventilation over the wall plate, there are gaps in the sleeper walls

I let insulation go under joists level with bottom of the plate

Strawberry netting is my favourite for support

Edge gap and against outside walls, prefer eps

Posted By: tonyEdge gap and against outside walls, prefer eps

I'm curious what the advantage of EPS is against rockwool?

Posted By: costley111And would it be fine to just use expanding foam to seal around the underside of floorboards for airtightness?

Expanding foam is not usually a good choice for airtightness, unless it is one of the special products intended for that purpose, because over time it can pull away from surfaces. Better to use a membrane or special purpose paint.

Costley, here's what I normally recommend for clients;

Materials...
- knauf earthwool as the insulation (decide how much you want to spend, so you can then choose on a sliding scale from loftroll with a lambda of 0.044, up to a rafterroll of 0.032)
- the above at 200mm will give you Uvalues of approx 0.22W/m2K for the loftroll44, down to 0.17W/m2K for rafterroll32
- 200mm would be good, 100+100. (or maybe 90+140 depending on which product you choose)
- no vapour barrier (let any moisture from the house travel through as it has always done, and it will clear due to the underfloor ventilation, as it was designed to do, not trapping more moisture inside the house. Plus you won't make it vapour tight anyway, just causing local pockets of high moisture buildup).
- vapour permeable membrane (what we use to wrap timber frame house walls with), get the cheapest one available, as it's not going to see any precipitation, hopefully.

Method...
- fix the membrane to the top of the first joist (at the floor boards), letting it hang down. Staples are good to get it started and straight, but follow up with some felt nails ideally to make it really secure.
- fill the first layer of wool into the joist gap, and the second layer against the membrane, so it sags down below the joists.
- pull the membrane up the face of the next joist (the face away from the insulation!!)
- fix the membrane all the way along the second joist, making sure the insulation is hanging nicely, sort of bulging a bit so that the successive rows of sagging insulation will be touching.
- keep repeating that process.

Watch out for...
- must maintain free air flow via the wall vent bricks. I didn't see these on you photos, but if they could be come covered by the insulation hanging below the joists, then you need to add telescopic extenders (plastic ducts to drop the air flow down a bit lower).
- around the external wall edges, the first joist may not start tight against the wall. Use some slips of rigid insulation board up this gap first. Bit of squirty foam to hold in place.
- take photos of any pipes that will get covered, so you can locate them in the future, maybe spray mark the walls or solum too, so your photo captures the markers.
- 110mm drains will probably drop through the floor?? do your bet around these with membrane and wool, then squirt a good ring of foam around, in the depth of the wool, and it will bodge the whole lot together nicely.

I've spent a long time (and continue) researching all this kind of stuff, and have been designing & building low energy houses, and helping people improve their existing houses, for quite a while, so I know this works. But of course the web is full of idiots giving advice, and I might be one of them

Best wishes, Donald J Trump.