Went to Eco-Build yesterday,
I saw Steve Allin's seminar, along with the guys that built the new Adnams building, on hemp.
Simply inspirational, what do you think?

Growing our way out of global warming?
Imagine if we could grow a building material that had a low density, yet high thermal insulation, with no thermal bridging and inherently air-tight.
As if that weren't enough it can also be used for carbon sequestration, instead of adding to the UK's Carbon Dioxide emissions it decreases the amount in the atmosphere. Don't believe the hype, read on. http://www.lhoist.co.uk/tradical/" >Hempcrete. http://www.lhoist.co.uk/tradical/pdf/Tradical_Information_Pack.pdf" >pdf.

I started a long thread about this when the forum first opened. Unfortunately, there seems to be no-one with real world experience of this material outside of the very well publicised trials. We'd love to use it in our build, but so far we are very uncertain about cost and long term stability, and the thermal properties would have to be carefully considered to fit our design and building regs.

Hey Tuna have seen the pdf's from Haverhill?
http://www.projects.bre.co.uk/hemphomes/" >Haverhill

>locking up 110kg of CO2 per m2, which I very much doubt is possible

That's a pretty easy calculation. The hemp will be mostly carbohydrate and lime is CaCO3. How much does the stuff weigh?

>The cost of a full wall built up 300mm thick internal plaster finish to external finish render is approximately £130/m2, this is comparable to traditional masonry construction
2006 Hutchins priceing book states "125mm blockwork externally; rendered and trolean finish; cavity with stainless ties;150mm blockwork inner skin finished with drylining and emulsion - £74.43per m2 net". SO while the price is not really "comparable" to an equivelent, conventional masonary finish.

>Use in France and Ireland for some years
For about 10 to 20 years, yet its being claimed to have a 100 year lifespan - maybe it will, I hope so, but where is the independent testing / verification to prove it? Other building systems generally have this.


>locking up 110kg of CO2 per m2, which I very much doubt is possible

>That's a pretty easy calculation. The hemp will be mostly carbohydrate and lime is CaCO3. How much does the stuff weigh?

Actually its fairly complicated - LCA can take teams of people months. But I now see that someone selling the product is claiming 250kg of CO2 per m2 of wall! Even if the wall was 500mm thick, the hemp could not contain this much Carbon Dioxide. A cubic meter of hemp, according to them weighs 110kg, so contains max 55kg of carbon, or less than 200kg carbon dioxide in a cubic meter - thats before any energy is used harvesting, transporting, mixing with lime, rendering, painting etc etc etc.


The system might be great - the future maybe. But why, then, the need for these extravegent, unverified and probably inaccurate claims?

Why compare to bricks? Bricks are expensive to buy, and to lay, and you've quoted a price for a part of the country where wages etc are seriously inflated to everywhere else. It would be fair if the hemp was also faced with bricks, but I bet the £130 price is for render. Compare a rendered finish with a rendered finish, & the claim of it being a comparable price is clearly wrong. Still not sure if the prices you've given are net or gross - the Hutchinsons are net, which is higher. In fact, working in the Midlands Hutchinsons prices are generally on the high side.

Just a note that there is a lot of interest at the moment on Hempcrete and Lime and due to the demand we successfully ran a conference last year which was very well attended, and due to this will be running it again on April 28th. An outline of speakers include:
Phil Horton (WISE Introduction)
Pat Borer (Hemp and Lime in WISE)
J. Garstang (Hemp’s Potential as a Multi-product crop.)
Bodil Pallersen (Danish Experience with Hemp growing, New research into hemp fibre mats)
Gary Newman (Hemp Insulation Mats for the UK)
Henry D O‚Thompson (Personnel experience using Hemp and Lime)
(Practical Demonstration Hempcrete: Peter Lawley)
Tom Morton (Light Earth and Clay construction and hemp)
Ian Pritchett (Commercial Experience with Hemcrete and new research)
Ralph Carpenter (Practical issues for using hemp and new research)
Stafford Holmes (Lime use in Construction and Small Lime production in the UK)

more information can be gained at http://www.cat.org.uk/courses/crs_content.tmpl?subdir=courses&sku=CRS_CONF

John Kearney
Centre for Alternative Technology
john.kearney@cat.org.uk

"The system might be great - the future maybe. But why, then, the need for these extravegent, unverified and probably inaccurate claims?"

This is true, and it is unlikely that hemp and lime walls actually lock up CO2, it all depends on the embodied energy of lime which varies, meaning that ~25kg/m3 could be sequestered or emissions could be 50kg/m3, this needs further no biased research not hype.

However the main interest is hemp as an organic crop for which it is very very well suited and can used as a break crop meaning it doesn't replace a food crop!! The amount of CO2 Hemp ties up is ~50% of its weight from none commericial data and including the costs of farming it organically, this would be a lot lower if it is farmed intensively as hemcore do. The embodied energy of hempcrete therefore is dependent mainly on the binder used, be that could be pure aerated lime, lime and cement as per tradical, or light earth or clay, or lime and an low embodied energy pozzolan e.g. rice husks. The monolithic walls that are formed do seem to perform very well thermally although this still needs futrther research to clarify how well and exactly what thickness is needed to deliver the same thermal performance as traditional layered walls despite having a higher u-value due to the thermal mass of the monolithic walls.

That conference at CAT is looking at using hemp as the basis of monolithic walls, looking at the binders that can be used and at how hemp is a profitable crop for the farmers, introducing a new way of treating the fibres with steam to produce fibre mats, looking at the possibility of manufacturing hemp insulation mats in the UK, looking at the use of lime in the UK and if localised production using wood or boimass burning would reduce its embodied energy sufficently, and looking at the practicalities of building with it for the self builder or the property developer. There is no commericial biass for the program it is an open investigation of a way of building that may have a very low embodied energy, be easy to do and lend itself to the construction industry and aid farmers.

The WISE building at CAT is being built using hemp and lime and CAT is currently investigating the thermal properties of hemp based monolithic walls.

There will be an open discussion forum at the end of the day for anyone to press home any points or queries they have. The delgates are all experts in the field with years of experience, and tickets are only £20!!!!!, it costs £75 for a commercial conference.

http://www.cat.org.uk/courses/Hempconferencedelgate.doc

I understand that hemp has a growing cycle of four months but please could someone tell me how many crops one could achieve in UK anually?

Gee Biff you do go on!

.

No you don't. That dot added nothing of substance to the discussion, while my post answered Isobel's post.

R

(for Reduce)

Eh? what does this whisper thingy do?

Ah, so Ted, you can't see a message from Isobel 11 hours ago and you can only see one from me (and this one) this morning?