In straw bale building we use a few key techniques that are unique to the trade.
Around our windows we have posts, so we need to put a notch in our bales to fit them snugly.
We do this using a Dewalt Alligator saw which is made for cutting building blocks, wood, drywall, insulation and Class 12 clay blocks. It also cuts straw bale very nicely, without throwing up a lot of dust.
I have also used a chainsaw to do this job. While the chainsaw does do an excellent job, it’s certainly more dangerous and a lot louder, plus throws dust into the air.
Here interns, Brendan and Rowena show us how it’s done using a template to ensure the right size notch. (Music by Money Mark)
Tools for straw bale building
Here we see our beautifully constructed straw bale walls. In front of them, two of the tools of the trade.
First up, we have the persuader. This larger than life hammer is used to knock the bales into alignment.
Secondly, we have the baling needle. This is threaded with twine and passed through the bales like a giant knitting needle in order to re-string the bales to custom sizes.
Dressing the Bales
The first thing we do to our bales is to dress them. This means we physically manipulate the straw in the end of the bale to make a flat and square end. This means our bales fit together better with fewer air gaps.
It is important to us to build with locally sourced materials. We have lots of clay, so are utilising that as much as possible. If this build were elsewhere in the country we would be choosing a different approach. We can’t just have a template for a ‘sustainable home’ that doesn’t factor in what local materials are available as transportation accounts for a huge amount of energy usage.
Our locally sourced materials
Our straw comes from a farm less than 5 miles from the site. We were able to go to the farmer, check the size and density of the bales… and even request that they be made as tight as possible… which they did! (The even cranked it so hard the baler broke – once the part was replaced, fantastic dense bales were the result – The best I have ever used!).
Most of the timber is from a local saw mill, using locally sourced timber.
Our gravel and sand is from a local pit.
The sheep wool insulation is all from Welsh sheep.
We are making clay plasters from clay dug on site.
All of our lime comes from Ty Mawr Lime, 60 miles away.
These are our obvious success stories….
Not so local
We have not been able to source everything locally, our smartply for example, came from the Czech Republic. Not great!
There have been other more subtle design choices that have allowed us to use more local materials. An example of this is how we have sheeted the roof. The conventional way is to use 18mm ply sheets, usually shipped across the country, if not Europe. We have opted to use larch planks from our local saw mill – It takes longer to build, but the environmental impact is far better.
This week we have been laying our car tyre foundations for our #BalesInWales cabin.
We have chosen to use gabion basket foundations. Though our Gabion baskets are reclaimed car tyres.
Car tyre foundations are the perfect choice for this build as:
They are cheap – actually the tyres are free, local garages have given all the tires we need as they have to pay to have them disposed of. We are only paying for the pea gravel to fill them.
They make a capillary break – Rising damp occurs when a porous material is used as a foundation. To combat this, conventionally a damp proof membrane (plastic sheet), is used to stop moisture coming up in the wall… but what if any moisture gets into the wall from above? It creates a paddling pool which our bales would sit in. Because neither pea gravel or rubber is porous, moisture can only travel downwards with gravity.
They find a use for an otherwise problem material. Tyres are said to have a life span of 30,000 years, so disposal is a big issue.
They are low embodied energy. To turn a tyre into a foundation, just takes the pea gravel and some porridge to power our workforce!
This last week we have been happily filling our car tyres in neat stacks, here is intern, Jamie showing us how it’s done!
The load bearing straw bale will be finished externally with lime render and chestnut shakes and roofed with a sedum green roof. Internally it will be plastered using the clay dug on site, and has a composting toilet, greywater treatment and solar hot water heater. Continue reading →