- Thread starter Ciaransmith
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It could make a big difference. If we assume that your wall is just the insulation and assuming that the internal and external heat transfer resistances sum to about 0.2, then the U value for your wood wool board is about 1.9 and for 4 cm of wood fibre about 0.8. This means that the wood wool loses about 1 Watt of heat per degree per square metre than the wood fibre. That's a BIG difference. The actual U values will depend on the wall as well, of course: they will be smaller and the difference would come out smaller too (even if it's the same wall or wall type). Still, you'd likely be looking at a significant difference in your U value.I followed @a twig advise and used wood wool on our walls, similar thickness and limestone walls. Its make a massive difference although that could just be the sorting of draughts out. Both rooms stay at a nice 16-18C temp most of the time. When we have the heating on it might get up to 19C. We used 25mm wood wool on the walls and then 300-400 rockwool in the loft.
We are actually thinking of wood fibre for our front room (early next year) the wife wants a snuggly warm room, although i'm not actually sure wood fibre of say 40mm would make that much difference than using 25mm wood wool. Anybody actually done the calcs and is it actually worth it for the extra cost/ time to faff doing it?
Nope. They need a good perpendicular connection with the special plastic washers. They are brittle.
Woodfibre boards at the same thickness would be a thermal improvement, as they are designed as insulation as well as a plaster carrier. Wood wool is simply a key. The various heat transfer stats are all available in the spec sheets via any of the standards retailers…it differs by thickness also. I use Eden for my stuffI followed @a twig advise and used wood wool on our walls, similar thickness and limestone walls. Its make a massive difference although that could just be the sorting of draughts out. Both rooms stay at a nice 16-18C temp most of the time. When we have the heating on it might get up to 19C. We used 25mm wood wool on the walls and then 300-400 rockwool in the loft.
We are actually thinking of wood fibre for our front room (early next year) the wife wants a snuggly warm room
A little more cost possibly, but I don’t see any difference in the faff or time level, both need a solid continuous contact to the bricks/stone, usually requiring an initial plaster layer to even out any undulations and remove air gaps. To be fair, the woodfibre boards have a bit of flex so in a smooth brick wall, you could possibly get away with out the initial leveling plaster coat.
Other than dubbing out the large holes I didn’t do the initial levelling plaster coat as it wasn’t something suppliers recommended at the time.
In the main living areas I did the plaster / mesh / plaster routine as outlined, but in one bedroom I just put on a 5mm skin coat with a 1:3 NHL to plastering sand mix.
I found the wood wool easier to skim over as it didn’t give - and then any cracks that appeared over the board joins I used a flexible lime based filler.
Overall therefore I found the boarding out and skimming faster and easier than directly plastering onto the wall.
While there may have been some small air pockets behind the boards which could have have partially impacted insulation performance, the overall improvement was significant compared to previous stone walls and there were no noticeable cold spots.
Re: interstitial condensation, given woodwool’s high tolerance of water and its vapour permeability frankly I wasn’t overly worried by that as a risk, and indeed didn’t see any evidence of it over the ensuing years
You may be getting mixed up with wood fibre insulation batts, which are helpfully still called wood fibre!
This is an insulation to go between boards.
Pavaflex - Eden Hot Lime Mortar
Pavaflex flexible insulation is installed between studs/rafters/joists and as part of multiple PAVATEX insulation systems.
edenhotlimemortar.co.uk
The link I sent for the isolair board is a rigid board to be mechanically fixed and plastered into. It won’t be flopping anywhere…
Overall, less than 100mm of combined proper insulation isn’t going to help much, if you can manage more. More than 200mm of decent stuff starts to diminish performance and space and cost…
It will, in an old timber frame there’s not much choice, many of our panels are a total of 80-90mm thick, with slightly pillowed plaster, and not all of that thickness is insulation. I’ve been using 50mm wood fibre bats sandwiched between 15mm wood wool boards on those.
Been looking at this last night as I’ve finally got the tanking off our utility walls, lowered what I can outside. Now looking at insulating the walls with wood fibre boards.
Seen uditherm online (wasn’t sure if was allowed to say where). It looks like the 40mm would have a u value of around 0.64 and 60mm around 0.49. Anybody know how this compares to wood wool boards?
Are these values anygood? Or something better for the same size that is obviously breathable.
Seen uditherm online (wasn’t sure if was allowed to say where). It looks like the 40mm would have a u value of around 0.64 and 60mm around 0.49. Anybody know how this compares to wood wool boards?
Are these values anygood? Or something better for the same size that is obviously breathable.
I think the wood fibre values are much of a muchness, it's the R value you want to compare and they're generally about 0.4.Bump. Need to get something ordered and fitted before xmas
We have fitted 80mm-100mm of steicoflex (between battens) or steicotherm (solid to wall with ejot fixings) and both systems have worked well. But 40mm or so will make a big difference.
I posted links to the technical sheets for both products in reply to you above. All the data is laid out there. Not sure what else you ate looking for from someone?
I’ll reiterate, woodfibre is an insulating product which you can plaster on, wood wool is simply a plastering substrate.
Lacan07
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Wood fibre boards will be better than wood wool boards for the reasons already discussed. For internal walls opt for anything between 40 - 80mm, anything thicker and you risk moving the dew point into the fabric of the building.
Ciaransmith
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- Matlock
Thank you for all the help, ive worked out i can stick the wood wool boards externall doubled up and then use wood fibre of propbably 40mm internal 