The technique is cheap, fast, ecological and durable, perfect for this context.
Timbrel vaults are one of TreeHugger's favourite building types because they do so much with so little material. Kris De Decker once wrote about them: "The timbrel vault allowed for structures that today no architect would dare to build without steel reinforcements. The technique was cheap, fast, ecological and durable." They are also known as Catalan vaults, and in the USA as Guastavian vaults, after Rafael Guastavino, who built them in Grand Central Station and the Boston Public Library.
Another master of the timbrel vault is Dr. Michael Ramage, who we first wrote about when he designed a vault for an early Zero Carbon house in the UK. He told the Guardian at the time: "The vaulting gives the house plenty of structural strength but obviates the need for embodied-energy intensive materials such as reinforced concrete." Now Ramage is part of Light Earth Designs, and has built a cricket stadium in Rwanda. All the virtues of timbrel vaults are on display here; it uses local home-grown labour, puts a lot of people to work because it is labour intensive, avoids imports, lowers carbon footprint and teaches building skills.
The tiles are produced from local soil, hydraulically pressed with a small addition of cement but do not need firing. They are laid up over temporary scaffolding, with a bit of high tech geo-grid for seismic reinforcing. I am an architect, not an engineer, but I suspect that the inherent qualities of timbrel vaults make that redundant. "The vaults follow the natural resolution of forces toward the ground, closely mimicking the parabolic geometry of a bouncing ball and evoking the cherished hilly topography of Rwanda."
The roof is then waterproofed and it is topped with broken granite, "blending into the natural palate while the granite adds weight and stability."
Whilst the language of the building speaks about progression and dynamism through extreme structural efficiency, the materials speak of the natural, the hand made and the human. It is a building made by Rwandans using Rwandan materials.The imperfections are celebrated – they are human and beautiful – and when combined with the layering of natural textures the building celebrates this wonderful place – a place where we have worked and lived for over 5 years.
I have always been amazed that these vaults stay up, they are so thin and often so shallow. But Kris De Decker explained:
The timbrel vault does not rely on gravity but on the adhesion of several layers of overlapping tiles which are woven together with fast-setting mortar. If just one layer of thin tiles was used, the structure would collapse, but adding two or three layers makes the resulting laminated shell almost as strong as reinforced concrete.
It is such a logical solution for a place like Rwanda where they have a lot of people to train in skills, a lot of dirt, and not much else.
When I first wrote about the Crossways House in 2009 I concluded that it showed that this old technology still had a role to play: "Let's hope we see more of this." I am totally thrilled to find out that we have.