Interesting projects. Thanks for the links. The French use hemp a lot more than most other nations. I'd be happy to see it used more here too. There's a hempcrete house a little way from us that's very nice.

Interesting links thanks Mike.

https://www.isohemp.com/en/technical-documentation

The thermal conductivity is 0.071 W/mK and it was applied as 100mm IWI, so not really very much good for thermal insulation, nowhere near to meeting UK building standards/regs for refurb.

Seems instead it was intended more to provide thermal mass and humidity buffering. Different climate zones perhaps have different requirements?

Though marketed as 'natural', the material does contain 20% lime cement which has a high carbon footprint. It's heavy, so high carbon to transport from Belgium. The claim is that this is all offset by carbon stored in the hemp fibres. I'm not sure that is locked away for geological time though.

Posted By: fostertomI tried digging into the French pages - how rusty, tho I once had a French girlfriend even - gave up.

Yes, I thought watching the videos might be easier than reading the text :)

Anyway, to summarise the first pilot project (RĂ©hafutur 1):

The location is in a UNESCO heritage site & former mining town 60 miles inland from Calais, south of Lille, so similar climate to southern UK. One key aim was to achieve the PassivHaus EnerPHit standard in an eco-friendly way, learning lessons that could be applied more widely.

The project was launched in 2012 as a partnership between the housing association (Maisons et Cités) and the University of Artois, with support from the regional Eco-business Creation and Development Association (CD2E), the French Building Federation, the Federation of Construction Employers Cooperatives, and others. Also included in the team, from day 1, were 2 architects, 3 engineers, an interior designer, a construction economist, & various others.

The refurb was carried out between June 2014 and June 2015, with a site-visit, education & participation scheme running throughout the year (over 1,200 visitors). Apparently Sophie Mörlin-Yron of the Ecologist magazine was one of the international journalists that visited; it would be interesting to find an article from her.

Various types of eco-insulations were used, including different insulation materials on each wall :
- 300mm hempcrete blocks in thin-bed lime mortar, the gap against the brick wall filled with hemp fibre, finished in gypsum or clay plaster (south-east facade)
- 350mm blown-in cellulose fibre (south-west facade)
- 350mm flax wool, fixed in two layers of 250 + 100 (north-west facade), behind metal studs
- 360mm sheep wool, stacked roll-upon-roll, behind metal stud walls (north-east facade)

..and elsewhere :
- 60mm medium-density wood-fibre board was wedged between rafters, with 240mm low-density wood-fibre board below that, on metal furrings, clad with plasterboard
- Sheets of 80mm expanded cork (chosen for its water and fungal resistance) were used to insulate the basement floor below the new screed
- Two layers of foamglass insulation (recycled glass) was used below the flat green roofs, bedded jointed & covered with hot bitumen & topped with an elastomeric roofing felt reinforced with polyester & glass mesh (not so eco-friendly, but with a 30-year warranty).
- Recycled textile quilt was used for acoustic insulation above the intermediate ceilings & in partition walls
At least on the partition walls, 80% : 20% gypsum & recycled-cellulose plasterboard was used.

The only non-eco insulation was 2 layers of phenolic foam, 120mm total, selected for its thinness, used to avoid undermining the foundations where the floor had to be dug out.

Where the internal walls met the external, most internal walls were cut back so that the IWI was continuous; the cut wall ends were stabilised by new reinforced concrete columns.

The building was monitored by the regional Civil Engineering & géo-Environnement Laboratory (LGCgE). 80 probes were used, measuring temperature & heat flow (on the internal surfaces, external surfaces, and boundary between insulation and structure of the external envelope), temperature & hygrometery (in the centre of the insulation), ventilation air flow & internal air quality, energy use was logged and the external weather measured. Various metrics were calculated including actual -v- predicted u-values, thermal inertia and thermal decoupling; plus acoustic performance, materials wastage, embodied energy, cost effectiveness, environmental life cycle analysis, etc.

At the end of the 1st year's use, humidity in the flax was excessively high (90%), hemp was lowest at 68%, with the other walls at 70%, although the building was still drying out. Hemp was performing best in terms of regulating thermal inertia & thermal performance. I'd love to fine the follow-up reports, but haven't yet.

I don't have time right now to summarise their second pilot (RĂ©hafutur 2, involving 6 miners' houses), but if, after such extensive evaluation, they've concluded that hemp is the favoured material for IWI (at least in the case of brick-built houses), I imagine that's a sound decision.