Hemp, lime and timber frame prefabricated panels are an exciting way of creating eco-homes. I recently visited a ecohouse (that doesn’t look ‘eco’) completed in August 2016 and built by Greencore construction and was given a guided tour by Julia Bennett and Ian Pritchett.
Prefab or craft, can you have both?
Having written a book on Contemporary Vernacular Design, I am very keen to retain craft skills as much as possible. However, as part of my book research, I interviewed architects Alan Dickson of Rural Design and Neil Stevens of Dualchas, both situated on the Isle of Skye and both producing beautiful contemporary vernacular dwellings, well suited to the tough conditions in the Highlands. What was intriguing to me was that both firms provide their own pre-fabricated dwelling options (coming under R-House and Hebridean Homes respectively) in addition to their usual bespoke dwelling design. These still look beautiful, and as Alan Dickson explained; there are 101 ways to get timber cladding wrong and one way to get it right, pre-fabrication is a way to get it consistently right. These prefab houses look beautiful and crafted.
Inspired by this, I have been keen to explore pre-fabricated construction to reduce time and worry on site (especially with Passivhaus builds). Which is why I was so pleased to attend the Greencore seminar at the recent AECB conference in July 2016. (strange how you have to go all the way to Norwich to discover what you need is only on your doorstep in Abingdon!)
Having provided the hemp construction system for The Triangle, Swindon (link), which was not prefabricated and built on-site during the cold and wet winter of 2010-11, Ian Pritchett could see that prefab, where panels are built in a dry factory, had to be the way forward (having been a doubter himself).
The natural prefab panels
Greencore offer a timber framed, hemp-lime filled, factory-made panelised system. But this is not SIPS – which is high in embodied energy, not breathable and studies in America have highlighted issues with poor airtightness detailing causing internal rotting. The hemp and lime lock up carbon and are both renewable and breathable offering a superior living environment. Greencore offer a bespoke design, working with architects at an early stage to ensure that design and construction are in synergy and there will be no surprises on site (or at least they are vastly mitigated – there are always surprises on site).
Ian is keen to point out that although you can use clay or lime plasters internally to complete the full breathability of the wall (and therefore a lovely atmosphere as well as very low environmental impact). You can also use standard plasterboard and emulsion paints and that these more commercially viable materials will still offer a pleasant living environment when combined with an MVHR system. I was surprised to discover a lack of fresh paint smell and assumed eco-paints had been used, but no, standard emulsions and an MVHR ventilation system delivering constant fresh air allowed smells to disperse very quickly.
The house is simple in design, with an attractive L shape, lovely open plan spaces, lots of light and beautiful vaulted ceilings with large rooflights in the bedrooms and bathrooms.
Simpler to achieve Passivhaus detailing…
Unlike the wide masonry cavity wall Passivhaus construction that I have previously used, the hemp-lime timber frame construction is easier to build in many ways. Windows are best situated in the middle of the insulation to retain best thermal performance and this can be achieved by sitting them on plywood boxes in masonry cavity construction, however stone reveals are not possible and aesthetically clients are not so keen on the deeper external reveals. The hemp-lime system allows you to position the windows centrally without ply-boxes as that is where the timber frame is situated. However, to fulfil client expectations (and this house is a commercial project), Greencore have used pure-nit boards to cantilever the windows closer to the external face of the wall. Purenit® boards, though more expensive than plywood offers much better thermal performance.
Using PHPP (Passivhaus Planning Package) software as standard they are able to predict heating requirements and always beat the predictions of the software on site. This means that the performance of hemp-lime beats the predictions of the PHPP and the heating demand is lower once built than was predicted by the software. This is very advantageous and defies the industry norm of as-built energy performance being lower than predicted in SAP (the industry standard for assessing energy performance of building as required by building regulations for all new buildings).
I am looking forward to working with Greencore on future projects.
August 30, 2016
There have now been eleven areas identified by councils for self build and custom build sites these are listed on the governments website here
If you are interested in a self-build or custom-build plot here is your chance to respond to the consultation. The Consultation closes on 18th December 2014 so place your responses here
For more information on the right to build and what Cherwell District Council are planning have a look at my previous post here
December 7, 2014
The Green Build Home Improvement Fund is back this Wednesday 10.11.14! Save lots of money on insulation and other energy efficiency improvements for your home. For more details on how to apply see here
December 7, 2014
The Green Deal Home Improvement Fund (HIF) will return at the end of this month (November 2014) providing a further £100m of subsidies for householders wanting to improve the energy efficiency of their homes. Sadly the initial £120m fund was used up very quickly (see my previous post about this) and many homeowners lost out. But it is good it is returning and on the previous scheme homeowners were entitled to claim up to £7600 on energy efficiency measures such as insulation, but we will have to wait and see what the new system offers. Here is a link to my post about what was previously offered. I will keep you posted with any new developments!
Here is a link to the Telegraph article on the subject.
November 15, 2014
The right to self-build is very political at present. Nick Boles is putting council’s under pressure to provide self build land for people who need to and want to build their own homes. In a quote from the Guardian newspaper:
So far, 60 councils across the UK have made 5,000 serviced plots available for people wanting to build their own homes.
This is good news for people frustrated with the lack of decent housing but unable to afford a plot of land. It is an antidote to the dominance of large housing developers in this country, if this has an effect it will be really nice to see pockets of interesting housing developments in the UK that will surely offer something better than identikit red brick. A really good example of where this has worked well is at Ashley Vale in Bristol (picture above and blog post here)
A local council to me, Cherwell District Council has also recently bought an old ministry of defence site, just south of Bicester which will be sold as self-build plots. How much you self-build will be up to you. You can have a serviced plot or the shell will be built for you. If you are interested further information on self build, Cherwell District Council is available here.
September 16, 2014
Clare Nash recently visited Ashley Vale self-build co-operative in Bristol which will form a case study in her new book (see publications page). She visited residents and interviewed them and also went on a tour as part of the AECB Conference in Bristol. This was a very informative tour, covering the site history and politics, including the difficulties of fighting off a developer and then gaining planning permission for 20 unconventional dwellings. A real inspiration, and certainly a good example of how to deal with the housing crisis. These homes are individual, larger than standard but at very high density. This would not have been possible with conventional house building planning rules and ‘the car rules’ typical estate planning. So it is a very good example of what could be done to solve the housing crisis. Ecomotive were the ‘developers’ who enabled this development to take place and it’s director Jackson Moulding was the founding member of the National Self Build Association (now the National Custom and Self Build Association (NACSBA). Ecomotive and Snug Homes are now keen to help future developments like this go ahead.
Interviewing the residents at Ashley Vale was a really rewarding experience as everyone was so keen on the development. People rated the community very highly and everyone seemed to know everyone, even the tenants. Local people in surrounding housing have also benefited with communal green areas and crime is very low. Three houses were open on the tour and it was interesting to see useful passive cooling techniques, such as low level openings and high level roof lights letting air circulate in a sun space. All the houses are timber frame with cellulose insulation, which creates a very breathable construction which is a very pleasant atmosphere to live in.
These houses were a lot cheaper to build than your average home. Plots cost £25-35,000, build costs were – £45-80,000. Cost per m2, around £500 which is extremely low, take note Mr Boles! Being green needn’t cost more than a traditional house, in fact if you do it yourself or as a community it can cost less!
Overall this is an excellent case study as it shows that the housing crisis needn’t be solved by identikit, soul less housing, instead you can identify a self-build plot and let people get on with building their own homes, creating fantastic communities as they do so.
July 23, 2014