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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorTuna
    • CommentTimeFeb 5th 2007
    At the excellent Green Day seminar held at the Cambridge Smart Life centre organised by Mark Brinkley, there was a fascinating talk about hemcrete as a building material.

    It seems magical - mix hemp husk and lime, take your lightweight timber frame and pack with the material, forming a wall 150-200mm thick (from memory) enclosing the studs. As it's continuously packed, there are no air gaps from ground to rafters. As it dries to rigidity, your frame is given significant strength. Packing it between battens appears to be a low skill task. Electrics can be piped around the frame and then encased as the mix is packed in. It's natural, breathable, fire resistant and highly insulative. It's hard not to think of it as a very flexible 'SIPs in a bucket'.

    So... what's the catch? Are people using it and getting the claimed results? Will it cost the earth to use it in practise, being a 'pioneer'? What is it's expected life span?
    • CommentTimeFeb 5th 2007
    What U value does it give you in a 200mm stud ?
    • CommentTimeFeb 5th 2007
    How is it applied Tuna?
    Do you think it will slump a little, leaving an air gap at the top of the wall?
    Thanks OJ
    • CommentAuthorTuna
    • CommentTimeFeb 5th 2007
    From this article, which is about the buildings discussed at the Smart life seminars:


    Taking a thermal conductivity figure for lightly tamped lime hemp mixtures of 0.09 W/mK (provided by Lime Technology), the following ÔÇśnotional' U values are achievable for a 100 mm stud encased in lime hemp mix with internal lime plaster and external lime render (these are approximate figures, subject to mix, spec, and so on):

    300 mm wall 0.29 W/m2K
    400 mm wall 0.22 W/m2K
    500 mm wall 0.18 W/m2K

    As for sagging - the material is mixed to a thick-porridge like consistency, and can either be sprayed onto a supporting surface, or tamped down between boards. It's not very compressible (only enough lime in the mix to make it sticky, not liquid), and dries to a rigid block, not unlike a sort of straw impregnated papier mache. There is no slumping - in fact the demonstration houses had the wall built right up to the (sheet) roof, with the top edge formed to an angle to meet the under-surface of the roof with no gap at all.
    • CommentTimeFeb 5th 2007
    Whats the advantage of hemcrete over warmcell?
    It appears to have a higher embodied energy and half the the thermal resistance.
    • CommentAuthorTuna
    • CommentTimeFeb 5th 2007
    In short the advantage is that it's structural. You build your walls out of it, rather than building using other materials and infilling with insulation. A hemcrete wall is claimed to be breathable, moisture resistant, and reduces insulation breakdown due to air gaps and sagging in traditional materials. It's also largely made from a product that is otherwise waste (hemp husks are normally left to rot on the fields).

    In green terms if sourced properly the suggestion is that the lime makes it carbon negative(?, I think).

    I sound like an advert for the stuff, which is why I posted - the talk made it sound like a wonderous building material, so I was trying to find out what was not being said.
    • CommentTimeFeb 5th 2007
    My understanding is that lime manufacture and distribution is energy intensive albeit less than cement.

    Warmcell in timber frame is also breathable, has minimal embodied energy and can deliver a U value of 0.15W/m2/C in a wall 300mm think.
    It sounds like a nice material to use, and if it aids structural stability it may cut down on the thermal bridging associated with timber studs. Sounds airtight as well - how expensive is it?
    • CommentAuthorTuna
    • CommentTimeFeb 6th 2007
    I'm not sure - that's part of the question. In the talk it was all very 'cheap and easy' - but these were professional architects and builders with years of experience in environmentally friendly builds. We're discovering as self-builders that it takes us twice as long and twice as much money to achieve what someone who knows what they're doing can.
    • CommentAuthorGuest
    • CommentTimeFeb 6th 2007
    It sounds like a good material. I like the principle of adding structural strength but do you need it really? Presumably your timber frame has sheet materials both sides to give something to tamp down to and these probably provide all the bracing one would need?

    Is it recyclable?

    Is warmcell really all that? Is it not more prone to slump, air gaps etc (it doesn't set hard like this lime/hemp mix)?
    • CommentAuthorTuna
    • CommentTimeFeb 6th 2007
    The battens used to form the hemcrete only need to stay there until it sets - a couple of days I think. After that internally it can be plastered or painted directly, and I understand the external treatment is usually weatherboarding. It's recyclable - you can crush it, mix in more lime and re-use it, (if I understood the talk correctly).
    • CommentAuthorGuest
    • CommentTimeFeb 13th 2007
    Research is being carried out on limecrete blocks. Apparently they will be available in Spring 2007. No details are
    available as yet. These really could be an alternative to aerated concrete block. Sadly they may not be available in time
    for my project though.


    • CommentTimeFeb 13th 2007
    Guest, Warmcel *can* be just poured in, when it indeed slumps a little, in a vertical wall situation. The prefered method is to blow it in, which also helps to fill inaccessible pockets in the construction (though you do have to make sure that all can be reached from the blow-in point, which need be only a 100mm hole in the sheathing/breather felt/whatever). Once blown it, it's very firm and doesn't slump. Contractors come equiped with light scrim, which they tack over any openings that have been left, to contain the blown Warmcel until the builder can complete any missing bits of facing.

    Warmcel's not structural at all; Limecrete could be a great alternative, accepting additional thickness, if it could do the structural job - but why build structural studwork and then infill with Limecrete? Seems the studwork's only there as a support for "battens" as temporary formwork/shuttering.

    As well as U-value, we need to start understanding the effect of massiveness (wich Hemcrete may provide, compared with e.g. Warmcel filling). The right combination of thickness and density, along with resistivity, can exploit diurnal temp swings to provide thermal performance way beyond that expected from the wall's U-value alone. Similarly structural cob has thickness and density but not much resistivity; this could just be where Hepcrete scores.
    Hello - we have considered using Hemcrete for our house, and we do feel that it is a wonderful material. We have probably decided against it on the grounds of cost, a large part of which was the timber frame needed for structural strength. This cost £24,000, almost the same as the Hemcrete itself, plus erection costs. The frame was needed to get a warranth from Zurich, because they will certify Hemcrete only as an infill material.

    So probably back to the Warmcell!
    • CommentAuthorGuest
    • CommentTimeMar 28th 2007
    Hi all, sorry I am in a rush today so I can't write much, but I was also impressed by Hemcrete when I saw it at Ecobuild a month ago, please have a look at the 25-page info pack on this web site for useful details on the product, building options and costs: www.tradical.co.uk I am considering using it for an extension I am planning for the summer, but I would also like to know more, especially if there is any drawback. All the best, maurizio
    • CommentTimeMar 28th 2007
    From http://www.constructireland.ie/articles/0215limehemp.php; this is significant:

    Carbon Sequestration
    A unique result of combining lime and hemp is their ability to act as a carbon sink. Data from Lime Technology Ltd in the UK proposes that 50 Kg of CO2 can be locked up per 1 M2 of lime hemp walling, and they estimate that a typical lime hemp house equates to roughly 50 tonnes of carbon per house, which in addition to embodied energy savings is a critical one-off carbon saving.

    This kind of one-time skewing of the carbon cycle is something useful that we can look out for opportunities to do. The object is to increase the amount of carbon around that's locked up in the unoxidised state, and preserving it there warm and dry for the forseeable, postponing its inevitable exothermic rotting/burning that will still happen eventually. That means e.g. using as much timber as possible for construction (as long as it's replanted), and is the best, possibly only sound argument for paper recycling.
    • CommentAuthorsalfa
    • CommentTimeJun 6th 2007
    I have discovered this forum by accident and thought i would add to the above seen I recently participated in a practical with hemp & lime at the Centre for Alternative Technology.

    I am not a big fan of it. It certainly has merits such as hemp being a wonder crop and the co2 sequestration; it has a good U-value; good air-tightness when blown; its fire-resistant and apparently recyclable. However, it is messy and caustic to work with. It has a high embodied energy because of the lime and takes 3 months to dry properly or you run the risk of growing fungi, even proper mushroom on your walls. It has no load-bearing capacity and is really only good for retro-fitting insulation. I can't see why it would be considered in a new build when other materials would be more advantageous.

    A reference we were given regarding embodied energy was a guy called Ian Pritchard if anyone wishes to persue this.

    Just to add to Salfa's comments above really (I was also at said practical at CAT). It is easy to listen to people plugging hemp and lime as the new wonder material that we have all been waiting for. But when you come to work with it and compare it to straw bale for instance you really have to ask yourself why you would choose it for new build. Long drying times, high embodied energy of lime, safety precautions, no structural properties, poorer insulation, not to mention that hemp is not widely grown in the UK (yet) and so transport and supply issues are a factor to consider. The carbon sequestration is also a point of contention it seems too, whilst lime does eventually re-absorb the co2 it let off in processing, this does not take account of the energy needed to fuel the furnaces for the processing, whether the hemp can make up for this is not cear as yet.

    Hope this helps!
    Posted By: salfaHi,
    I am not a big fan of it. It certainly has merits such as hemp being a wonder crop and the co2 sequestration; it has a good U-value; good air-tightness when blown; its fire-resistant and apparently recyclable. However, it is messy and caustic to work with. It has a high embodied energy because of the lime and takes 3 months to dry properly or you run the risk of growing fungi, even proper mushroom on your walls. It has no load-bearing capacity and is really only good for retro-fitting insulation. I can't see why it would be considered in a new build when other materials would be more advantageous.

    All of the first bit is why hemcrete is so useful - what other panels can boast those attributes?
    But your list of 'drawbacks' doesn't cause me any problems. Why would you want fill panels to be load-bearing?
    As for caustic, have you done much work with OPC? It is far harsher on the human skin than lime. And as for energy - look at the respective kilning temperatures and methods of manufacture between OPC and lime. I know which I would choose...
    Straw bales have their place, but can you imagine something like the Adnam's store being built out of bales? ;-) I'm sure, had it been possible, Ian Pritchett would have considered it, but the practicalities and the scale meant that bales where out of the question.
    • CommentAuthorMrT
    • CommentTimeJun 11th 2007
    Lime hemp combination does have structural strength hence you can use it as a floor structure. Also the point is that the extra strength in the mix reduces the need for large number of timber sections. So it does have load bearing capcity and this is why people are looking into making hempcrete blocks as an alternative to concrete blocks.

    Can the use of strawbale every be a serious proposition in high denstiy areas which are common to the UK? Strawbales are great in areas like East Anglia where lots of straw is available.

    Hemp is a useful crop. Many parts of it can be used for different applications. It was grown extensively in the UK in the past and was used in the manafacture of rope for the rigging in sail ships as well as the sails themselves. Personally I'd rather see a field of hemp to oil seed rape.
    Re the sequestration issue, to quote from Ian Pritchett's figures: "Hemp absorbs CO2 as it grows and the manufacture of lime (and our Tradical® binder) is responsible for CO2 emissions. The net result of combining the two to form Hemcrete® is still carbon negative i.e. the hemp takes in more CO2 than the binder production emits. The typical figure for Hemcrete® wall mix is 110kg of CO2 per cubic metre of Hemcrete®"
      CommentAuthorothman ali
    • CommentTimeJun 12th 2007
    • CommentAuthorbiffvernon
    • CommentTimeJun 13th 2007 edited
    If that was made of hempcrete I'm going off the idea :(

    PS Does the whole building turn to face the wind?
    • CommentAuthorcharlz
    • CommentTimeJun 15th 2007
    hi there, anybody know any builders/installers who have worked with hemcrete, i am keen to use it on a small extension and would like to talk to someone who has built with it b4 going ahead.
    • CommentAuthorDing
    • CommentTimeNov 23rd 2007
    I understand there are a number of buildings that have been completed using the product and another few on site so there should be some builders who can give you feedback on working with it. I also think that a couple of the projects have been small extensions.

    Think the best people to contact would be Lime Technology who make the product, see: - http://www.limetechnology.co.uk/pages/contact.php
    • CommentAuthorevan
    • CommentTimeApr 16th 2010
    Trying to decide on the wall make-up for my extension.

    The standard 250mm Hemcreted timber frame with render on the outside seems fine. The only drawback is the expense and the finicky work of rendering and finishing it.

    As an alternative I was thinking about 200mm of the lighter "insulation" Hemcrete, with something like Larch cladding on the outside. Might actually work out cheaper, and would look nicer.
    Still have the benefit of thermal mass (compared to timber frame with insulation).

    Any thoughts on this, Hemcrete people? I'd rather get your opinions first before bothering Lime Technology..
    • CommentAuthorjemhayward
    • CommentTimeApr 16th 2010
    Compared with mixing the hemcrete, rendering the outside is a breeze. If you are having a boarded up internal wall finish, then insulation grade hemcrete will be ok, but remember its thermal mass is lower. Rendered hemcrete looks really lovely, especially if you hand finish it and soften the curves...
    Hi everyone, Interesting to read your posts. Just wanted to let you know i am a builder with experience of three hempcrete builds designed and built by myself, including an extension to a victorian terrace house and a garden office. I am currently setting myself up as a specialist in using hempcrete for new build and period structures repair/renovation. So if any of you require a hempcrete builder please look me up. Williamstanwix248@hotmail.com
    • CommentAuthorearthed
    • CommentTimeJul 22nd 2010
    Hi all, I am a builder of timber frame cob and straw bale structures. What everyone seems to be missing out here is the politics of hemp. As far as I can make out there is one company allowed by the UK government to process hemp. They supply to Tradical who seem to have a small 'r 'next to all there 'products'. Er where is the competition? Hemp lime only seems like a good idea if I can do it myself, I.e. choose a producer of hemp, and lime and make the material myself as they seem to do in France! Until then if I have to buy a 'product' supplied by one manufacturer then no thanks. I would suggest looking at light straw clay as an alternative, although again drying time is an issue in our wonderful maritime climate, and no it's not load bearing. If anyone has any information regarding the history of hemp in the UK and the current monopoly on production I would love to hear.
    Hi earthed, apart from Tradical products there are other producers of bailed hemp suitable for construction, most of these market the hemp as horse bedding but some are also suitable for construction. There are also two products to choose from for the lime binder- Tradical HB (made by lhoist uk, lime technology Ltd and castle cement in the uk) and Batichanvre (which comes from st astier in france). Hempcrete originated from france and indeed it is a french company - Lhoist that has pioneered its use in the UK (along with limetechnology Ltd who are a british company) and as far as i am aware the french use the same technique as we do- buy a lime based hemp binder and mix it with hemp shiv. There is no reason you cant do this yorself and if you really wanted you could make your own binder using Hydraulic lime and mix it with hemp sold as horse bedding- the only problem here is that it might take you a while to find a mix that works and drys quickly enough. I have also built straw bale structures and studied there strength in construction at university and the main advantage hempcrete has over straw bale and cob is that it has national building control approval in terms of its structural strength and thermal properties. There are three different mixes you can use, each with different structural and insulation ratings, as long as you use the correct mix you get building control approval, where as straw bales are not the same from one farmer as another and as such it is harder to get building control approval.
    I will try and get more information about the history hemp in the uk.
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