What U value does it give you in a 200mm stud ?

From this article, which is about the buildings discussed at the Smart life seminars:

http://www.constructireland.ie/articles/0215limehemp.php

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Taking a thermal conductivity figure for lightly tamped lime hemp mixtures of 0.09 W/mK (provided by Lime Technology), the following ‘notional' 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
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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.

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.

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?

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)?

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.

http://www.limetechnology.co.uk/pages/randd.php?page_id=78

Luket.

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!

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.

Hi,
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!
Sam

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.

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.

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..

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

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.