Breathable insulation is essential in a 'breathable' environment. OK - I can hear you asking - what IS breathable insulation? You've all seen lorry loads of that polyurethane board stuff being carted around - with foil on either side of the sheet. That's kingspan, or something like it. Horrid stuff - made from a chemical soup, constantly releasing toxic vapour into the air in your home, and it certainly isn't breathable. Next is fibreglass - a bit more breathable - sure, vapour can pass through it, but because it is glass, it is incredibly prone to condensation. It gets wet. It's what they blow into cavities which then get wet, and you have to have the cavity insulation removed again. Every roll of fibreglass in the United States has a cancer warning printed on it - I wonder why? Shades of asbestos here... So forget kingspan, forget fibreglass - what's left?
Well if you ignore the marketing hype of the billion pound companies that make the above mentioned chemical baddies, there is a new breed of environmentally friendly, breathable insulation that stays dry and keeps you warm.
Top of the list has to be sheepwool. Now then - you've never seen a mouldy sheep on a hillside have you? It doesn't get mouldy, doesn't settle or break down like fibreglass does. It doesn't suffer from condensation like fibreglass. It won't give you lung problems when you inhale it like fibreglass.. It doesn't outgas toxic chemicals like kingspan. Guess what - it's really carbon neutral. All it takes to produce is a few farting sheep on a hillside.
Now - sheepwool on a mountain, and sheepwool in your house are two different things. It's clean, it doesn't smell, but it does need to be treated to stop moths finding it - remember your mum and the mothballs in the wardrobes? There are a few producers of commercial sheep wool insulation - but only one produces a pure, unadulterated product with a guaranteed treatment that is totally bug resistant: Cosy Sheepwool Insulation. Most other producers use a borax treatment which can come off, and leaves the wool exposed to bugs.
Now then - there are things like breathable insulation board which we recommend for use in timber framed buildings and which can be used to add insulation value to a solid walled building - either as internal, or external wall insulation. We are VERY wary of recommending any form of Internal or External insulation at the moment - there is just too much scientific uncertainty as to whether these things really work. We do specify breathable hemp fibre insulation boards in roof upgrades - Pavatherm is one such example. Really good stuff. It's essentially hemp insulation - but in rigid boards which have a tongue and groove structure.
Internally we are starting to use hempcrete. It's available in blocks, or it can be done as a rammed product - pushed into a formwork to form a solid wall - but breathable and very insulating. If you only have room for a thin coating on your walls, hemp lime is great - normal lime plaster with hemp added to give it better insulating properties.