New timber frame natural build - Introduction and Concrete Free Foundations.
This is the first in a series of blog posts showing the build process of our new eco house currently under construction in Bishopston, Bristol. This exciting project is a one bedroom dwelling to the rear of Room 212 on Gloucester Road. As well as showcasing various sustainable building methods, including using natural, low embodied energy materials and a breathable wall system, it is also an example of building a compact home in a small urban space.
We'll be detailing different elements of the build as it develops over the next few months, but here's a little introduction:
Natural, Breathable Construction
Originally this build was going to be made from straw bales. As a space saving measure we have ended up using this timber frame system. But we aim to preserve some of the features and benefits associated with straw bale: The walls will be insulated with a layered build-up of sheepswool and wood fibre board. Both have a low embodied energy when compared to petrochemical based insulation, and are made from waste materials that are available locally.
The timber frame design borrows from the designs of Walter Segal, whose simple house building system aimed to make it easier for people to build their own homes - his designs used off the shelf timbers fixed together using bolts so minimum professional tools were required, and the more difficult skills such as bricklaying were kept to a minimum, to make building your own home accessible and affordable. We'll be showing you how this frame design works.
This building aims to be an example of how a small space can be a functional and ample place for living: do we need to have large homes, when larger buildings mean larger energy consumption, and we have less and less space in our cities, as land and property prices are skyrocketing.
But first.. Concrete Free Foundations
As a high embodied energy material, minimum use of cement, the key ingredient of concrete, is paramount. More than 5 % of global CO2 emissions come from cement production. Most new buildings pour many tonnes of concrete into the ground which is simply not necesary.
There are various methods to minimise or eliminate the need for concrete. One way is using a pad foundation instead of a strip foundation. This means that instead of a deep trench filled with concrete going all the way around the building, square holes are dug at intervals which are filled with concrete and used as pads for supporting posts for a timber frame.
Alternatively a different material than concrete can be used. Compacted stone, gravel or hardcore perform a very similar function to concrete and are cheaper and a lot less damaging to the environment. Limecrete is a similar material to concrete but uses lime as its binder, which has less environmental impact than cement.
For this project we have combined these two approaches: Instead of a complete strip foundation we have designed the build to have 2 sides of strip foundation, across which the timber frame will span. So we have two trenches which are filled with gravel, compacted, and then capped with a layer of limecrete. A plinth of reclaimed brick rests on top of this.
This photos show the trench already mostly filled with gravel, upon which we are laying a 400mm deep layer of limecrete:
Here we see Jules posing in the sunshine as he lays the brick plinth ontop of the limecrete slab.
And here is the completed foundation. Only the thicker brick walls at either side are loadbearing - the frame will span between these. The brick walls at front and back are just filling in so there is no gap under the building, and they don't sit on a deep foundation. Next week we'll show the next stage: Timber frame.