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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorMike1
    • CommentTimeJan 11th 2022
    Thought this may be on interest. Following trials of various natural insulation materials over the past decade, (including wool, flax fibre, cellulose fibre, hemp), a housing association in France has started a pilot project to renovate 50 listed houses, 30 using hempcrete, 20 using hemp blocks (with airtightnesss, MVHR, etc). The longer-term plan is to expand the scheme to 1,000 homes.

    Brief introduction in English: https://www.isohemp.com/en/hemp-solution-heritage-renovation
    And a few videos on the first experimental renovation (house to offices), in French:
    - Overview https://www.youtube.com/watch?v=0t84yWAu9TU
    - Insulation https://www.youtube.com/watch?v=QkR4WATzp0Q
    - Airtightness https://www.youtube.com/watch?v=yad8G1Wkfbw
    • CommentTimeJan 11th 2022
    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.
    • CommentTimeFeb 20th 2022
    Eh, les Francais - that such a different world lies only 60 miles across the water! That in France an org like that researches and decides and can impliment their optimum system, regardless of mainstream.

    I tried digging into the French pages - how rusty, tho I once had a French girlfriend even - gave up. I didn't find much in the way of either technical justification or practical/installation to explain the strong decision. There are architect's drawings and details but don't really describe it. Anyone understand it better?
    Interesting links thanks Mike.


    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.
    • CommentTimeFeb 20th 2022 edited
    For use making a hempcrete house it's normal to mix the hemp fibres and lime locally, so there's no need to transport the heavy lime from abroad. The law here is still quite restrictive on growing hemp so it's more likely the hemp would have to be imported although there are some UK growers. The walls tend to be quite thick, as is normal with any build using natural insulation.
    • CommentAuthorMike1
    • CommentTimeFeb 21st 2022 edited
    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.
    • CommentAuthorMike1
    • CommentTimeFeb 21st 2022 edited
    Posted By: djhThe law here is still quite restrictive on growing hemp so it's more likely the hemp would have to be imported although there are some UK growers.
    Just been checking that and (for the moment, at least) EU Regulation 1164/89 applies in both countries - so in theory it should be similar.

    Seems it's the implementation that's different. In France growers apparently need to obtain seed from a national cooperative (hemp-it.coop, who share registration details with the police), use an approved processor, are likely to undergo spot-checks, and are advised to warn their local Gendarmerie. As is often the case, the UK have tied it in red tape by requiring farmers to pay for a two-stage license regime & allegedly changed their mind after granting licenses.

    It is certainly a more popular crop in France - they now grow around 20,000 hectares (the World's 2nd producer after China), an increase from 700 hectares in the 1960s and 10 x more than the UK. One of the hopes of those involved in this refurbishment roll-out is to develop a sustainable local hemp industry among local farmers.

    https://www.interchanvre.org/i have info on the French industry in English.
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