Insulation Questions

[a twig]

Hi gang,

Two hopefully quick questions on insulation -

1) Downstairs bathroom has cellar beneath it. Floor is floorboards, with hardboard to level then clicky laminate stuff on top. The floor is absolutely freezing cold at the moment, what insulation can I put between the joists to try and improve this? Obviously cellar can get a bit damp, so guessing breathable stuff required?

I've seen a lot of people use Celotex rammed up against the underneath of the floorboards - bit nervous of doing the same though.

2) Interior insulation for solid stone external wall - planning on using some woodfibre board, then slapping some lime plaster over it after.
Can I fix the woodfibre boards straight onto the wall using the plastic washer thingys to avoid thermal bridging? Or do I need to lime plaster, then board, then plaster again as some "instructions" on the web seem to suggest?

Cheers!

 

[Lime]

Under the floor above the cellar I'd use an insulation that is pleasant to have around in a domestic environment.
It would also have to form a tight insulation seal against the underside of the floor and not allow any channel of free air to circulate.
I don't see how block insulation can accomplish the latter.
Inevitably there will be gaps and channels between the dead-flat insulation and the far-from-flat floor boarding that will allow air to circulate and take the heat away from the floor.
Almost all other insulation is fibrous in some fashion and most are very unfriendly to humans.
I assume you do not intend to take up the floor?
Consequently wool insulation is the only option left.

 

[TheRoost]

Would you change the bathroom floor or is it recent?

If not wanting to insulate from underneath, maybe you could change the flooring type and/or insulate underneath that - At the back of our house we have a solid concrete floor - the room with 20mm solid wood flooring laid over is surprisingly warm to touch (no insulation underneath) yet the adjacent ceramic tiled kitchen floor is freezing.

We also still have some naff laminate flooring in hallway (suspended floor) this has the cheap thin foam underneath, and never feels cold to walk on.

 

[a twig]

Happy to insulate from underneath (indeed it is preferred as we've only just put the flooring down and I definitely ain't pulling it up again in a hurry!) I was fairly set on Thermafleece anyway, just seeing some other stuff on the interwebs made me question myself - so Thermafleece it is then, thanks.

Any ideas on fixing the woodfibre boards? Zebra I believe you have used a fair amount of this stuff in your place relatively recently, how did you fix yours?

 

[bennoa1]

I use 25mm fibre boards (wood wool board) and use 60mm stainless screws with stainless penny washers or the large plastic spreader washers that are recommended with the board. Got the boards from Skandia in north wales (just around the corner from Black Mountain).
I use the Black Mountain fleece rather than the thermafleece.
bennoa1

 

[a twig]

Thanks bennoa1, was that fixed onto stud or directly onto the wall?

 

[bennoa1]

Onto wood but don't see why you couldn't attach to the wall.
Thoughts it was a ceiling in which case you'll be securing to the floor joists.

 

[Zebra]

Sorry, been busy. Yes, I have used a lot of woodfibre boards.
I'm afraid that where I've used them internally to insulated solid 9" walls (not having enough overhang to insulate externally), I did lime plaster first to level it up, and then attached the boards on top using the plastic washer things. I just didn't want any gaps where air could circulate or moisture could accumulate. How likely this is, I'm not sure, but then I quite like lime plastering anyway, it only costs you a bag of lime and a few bags of sand, and as it's only a levelling coat and doesn't matter about having joins in it, you can do a wall over a consecutive number of evenings....

 

[Tony.]

Under the floor above the cellar I'd use an insulation that is pleasant to have around in a domestic environment.
It would also have to form a tight insulation seal against the underside of the floor and not allow any channel of free air to circulate.
I don't see how block insulation can accomplish the latter.
Inevitably there will be gaps and channels between the dead-flat insulation and the far-from-flat floor boarding that will allow air to circulate and take the heat away from the floor.
Almost all other insulation is fibrous in some fashion and most are very unfriendly to humans.
I assume you do not intend to take up the floor?
Consequently wool insulation is the only option left.

Would kingspan/celotex cut between the joists, sealed with a silicone sealant and topped with a suitable foil tape such as tescon tape
http://www.travisperkins.co.uk/p/tescon-profil-roll-60mm-x-30m/788577/3893480

I did this to some walls and it made a huge difference to the heat loss

 

[Roger H]

If I were insulating under joists with kingspan, I'd suggest cutting the panels so they are a loose fit e.g. 5mm gap all round, and wedge them into place with little kingspan off-cuts.

Masking tape the timber beneath, then foam fill the joint. That should prevent any vapour passing upwards or downwards through the floor.

 

[El Greyo]

Hello Zebra

Can I ask what make/brand of wood fibre boards you used on your walls? Did you use lime plaster directly onto the boards?

We are about to do something similar. We don't have much space to play with so will need something not too thick that we can put a lime plaster directly onto.

Thanks

 

[bennoa1]

I've plastered straight onto the wood wool board - they do have a course finish offering a very good key. Probably put 30mm of lime hemp plaster on them (25mm boards). Would have to be a think skim on the 15mm boards as they are nowhere near as sturdy as the 25mm board.
I use Heraklith BM (I think) from Skanda in N.Wales. They also sell the big plastic spreader washers. Used stainless screws to secure them - got these from Scerwfix!
http://www.skanda-uk.com/heraklithProducts.htm#HBM
They were attached to stud but you could attach to a wall or ceiling but I'd go with 15mm on ceilings due to the weight.

 

[Zebra]

Let's be clear: there are two different types of board: wood wool, and wood fibre. Bennoa1 is talking about wood wool boards, whereas a twig was talking about wood fibre boards. Both are breathable. Both are possible to use inside and out. Woodfibre is more thermally insulating.
Woodwool board is quite easy to plaster onto, as bennoa1 says, they've a coarse surface and offer a very good key. You can put an ordinary lime plaster straight onto them. Hemp would be excellent too, but is not necessary. The 15mm boards are fine with plenty of fixings, as long as the joins are supported and there's no movement in them before you start. I've actually gripfilled the edges together to prevent cracking on ceilings.
As for woodfibre boards, I've used these as external wall insulation, with a special plaster base coat and top coat, with mesh in between, applied by professionals.
I've also used them internally where I've plastered over them myself using a fat lime plaster. It's not as easy as using woodwool boards - the plaster does tend to peel back a bit as you're putting it on. As the boards are not very hard, you have to use the mesh in between the first and second coats. I tried at first without, and the wall was too easy to dent afterwards, so I took it off and tried again. I think I overwet the boards first time too. I've only done one experimental wall so far, and I'm sure I will master the technique soon.
I used "Steico Protect H" boards externally. I don't think these are available any more, as the company selling them closed down. Internally I used a combination of the leftovers of the Steico, and, if I remember correctly, Ty Mawr's "Homatherm Q11."

 

[beaufontboy]

I had a similar dilemma, my plaster wasn't in great condition, so took if off, boarded with cork straight onto the wall then going to lime over the top
(Havent started the floor yet but I am going for thermafleece)
https://www.dropbox.com/sc/d6p4rbcp9yqvs8e/AADs_Y-sIwzwppwEbkZGFawCa

 

[El Greyo]

Thanks Zebra

I was hoping that there would be a best of both worlds - as board with the thermal performance of the wood fibre but with a key of the wool wood. I haven't seen that perfect combination yet though.

 

[Zebra]

I suppose you could layer them. Ah, no, you said you were short of space. Well perhaps go for the woodfibre then, and put up with the fact that they're a bit trickier. I'll share any experience once I get around to plastering those walls!