Can you please expand on the statement in bold.. sorry I don't understand thrust of the message.
Thanks
- Thread starter AndyC
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Thanks
Mighty interesting. Mineral/Glass wool is more breathable than wood fibre boards........this is news. So, technically if it was possible to fix flexi mineral/glass wool batts for the purpose of IWI it would satisfy the breathability criteria. I wonder what are the disadavantages or glass/mineral wool over wood fibre/hemp fibre?Apologies if I'm going to tell you things you already know about breathability.
Breathability is measured in terms of Water Vapour Diffusion Resistance Factor – aka μ value (pronounced "mew"). The μ value is how much harder it is for water vapour to pass through the material than the same thickness of standing air.
I got ChatGPT to reverse engineer the μ value from their technical sheet where they say
That should mean the sheet has a μ value of 2, but I'm no expert.
Here's a list for comparison
Typical μ Values for Common Materials:
p.s. I do agree this won't have strong insulating properties. I have a giant table of insulation types and their R-values (mostly breathable types of insulation). Let me know if it's of interest and I'll share it. Are you trying to get a flat, insulated surface to skim over? I came across this product for uneven walls. Maybe it's of interest? No experience of it yet myself.
- Concrete: μ value around 50 to 100
- Brick: μ value around 10 to 50
- Gypsum Plaster: μ value around 6 to 10
- Lime Plaster: μ value around 5 to 10
- Mineral Wool Insulation: μ value around 1 to 2
- Wood Fibre Board: μ value around 5 to 10
- EPS (Expanded Polystyrene): μ value around 30 to 70
- XPS (Extruded Polystyrene): μ value around 80 to 200
- Glass Wool Insulation: μ value around 1 to 2
In addition gypsum vs lime plaster equal breathability, up until this post have always thought lime plaster was much more breathable than lime. This is a revelation.
Another revelation: Gypsum board has mew/mu value of 8.3 according to chatGPT. Surely this can't be correct as such boards are considered non breathable.
Very confusing
fernicarry
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I think what @Kearn is getting at is that some materials handle liquid water better than others. Say you have a leaky roof or a burst pipe then that aspect becomes quite important in terms of the damage done. More so if its happening unseen inside a wall build-up. Plasterboard turns to mush and permanently loses its mechanical strength, lime plaster carries on as if nothing happened. Glass wool acts like a sponge I think so I wouldn't particularly want it inside a wall where it might meet penetrating damp whereas sheep's wool is supposed to be excellent at drying itself out. The hemp batts I use here are a bit funny because they often feel damp to the touch when temperatures fall (due to being hygroscopic?) but they do dry out quite readily. I imagine thats a good property for buffering changes to moisture levels in the building.