breathable wall insulation

[fostertom]

What do we think of hemcrete (hemp husks in a lime-based binder) sprayed on say 75mm thick, inside and/or outside? Breatheable, medium insulation, medium thermal massiveness, can follow wobbly walls, keeps all the wall's thermal massiveness working as one (which ordinary internal insulation destroys), so allowing thermal massiveness to fulfil its role as a fair alternative to U-value. Hemcrete externally would be best, as all the wall's working bits and most of its thermal massiveness are retained on the warm dry side of things.

 

[andrew gayton]

A new method to me..................... but it sounds fine in principle. I will need to look into this.

 

[middi]

The problem with a 75mm thick externally applied insulations is the loss of eaves detail at the gutter and overhang level, ecpecially where original oak angled sprockets are in existence.

 

[fostertom]

Yes, every case different. Tho external is thermally best, Internal generally a v poor alternative, in the case of Hemcrete internal is almost as good - it has some unique thermal properties arising from its particular ratio of conductivity to density.

 

[sue gazzard]

I have disappeared from this one for a while - mainly because I've been persuaded that as the wattle & daub on my building is mostly in good condition (and where it isn't/has shrunk we can use lime mortar internally to fill it out), a breathable membrane plus 3 coats lime render on the outside plus roof insulation and work on the centuries of paint on my draughty original windows will make for a very comfortable building without introducing any additional insulation. But I confess I am fascinated by this Hemcrete.....has anyone tried it??

 

[sue gazzard]

ps why does it need to be 75mm thick? Is itr not poss to go for a compromise thickness to achieve some insulation value without ruining the appearance of the building's profile?

 

[Nemesis]

Marianne Suhr:

http://www.periodliving.co.uk/Features.aspx?Action=826436321&ID=978621c5-e3d2-451c-be9d-aa760933f06e

http://www.periodliving.co.uk/Features.aspx?Action=826436321&ID=ef9b2147-3d68-4df2-a4e5-b070485b4ee4


http://www.backtoearth.co.uk/


http://www.backtoearth.co.uk/products.html

 

[sue gazzard]

Nemesis, thanks so much for those links. I really hope I might be in time to sub Hemcrete panels on my own single storey extension due to start construction soon. It sounds really fantastic!

In terms of using it to fill in miscellaneous gaps, (where it would be inappropriate/ too costly to bring in a specialist contractor) how does one get hold of sprayable/pourable version in relatively small quantity?

 

[Nemesis]

I have no idea - I've been reading Marianne's house stuff (the latest episode revealed her pregnant and desperate to finish the place - she must be a mum by now...) and that's where I first heard of it. It looks to me to be solid stuff not very liquid, but for more advice call the people who sell it or the SPAB free technical helpline is my suggestion.

The site says:

Coverage
Coverage rates vary depending on thicknesses and methods of application. 300mm thick wall - approx. 300l per m² spray application or up to 450l per m² for shuttered, 500mm thick wall - 500l per m² for spray application or up to 750l for shuttered

.

 

[Johneds]

The manufacturer of Hemcrete claims the product is 'a monolithic material that is inherently air-tight'. It goes on to say 'this high level of air tghtness minimises the heat lost through air leakage'.

Air-tight and breathable at the same time. How does it do that then?

 

[Nemesis]

Same way as lime?

(You could ask the manufacturers and report back...)

 

[Johneds]

Yes, I might ask. being both air-tight and breathable is a contradiction of terms. It isn't the same as lime mortar. Lime mortar is breathable but not air-tight.

 

[Flyfisher]

Could it be the same sort of principle as waterproof but breathable clothing - keeps out the rain but the breathability prevents you getting all sweaty.
Or, for something even more counter-intuitive, the same principle is used for breathable waders.

More seriously, I suspect that "air-tight" is probably used in the draught-proofing sense than the absolute sense.