Our mission is to accelerate the transition to zero carbon cities. We always knew it was going to be a big challenge, and that to do it we couldn’t use the same old construction techniques which haven’t been improved on for decades.
So we did the smartest thing you can do when faced with an enormous challenge. We asked for help.
We worked with Professor Chris Gorse (below) and his team at Leeds Beckett University to co-design a housing solution that would allow us to meet our goal of building zero carbon developments to a world class standard.
To help us do this, it had to do three things:
- Use the lowest carbon construction materials, to minimise emissions during construction.
- Have thermal insulation properties so good that it would need only the minimum amount of heating, dispensing with the need for a gas boiler and therefore preventing the emission of huge amounts of CO2.
- Be durable enough to outlast our generation, and the next, and be replicable on a mass scale, for wide-spread adoption.
The answer was to use a construction material that has been used in Scandinavian designs for its thermal properties for years, but is not used by the majority of the UK construction industry: wood.
Chris’s team at Leeds Beckett conducted 3D modelling of the thermal and hydro-thermal properties of the timber framed solution, applying their knowledge from lab work and whole building tests, to ensure that the design would mean the building was so well insulated it would only require a fraction of the energy to heat it compared with a traditional masonry house. They also ensured that the building’s temperature would always be comfortable, and that ventilation systems would ensure the building never over-heats.
Why use wood?
Wood is lightweight, has a similar strength to weight ratio as steel, is easy to work with and has far better thermal insulation properties than masonry or steel.
And, as an added bonus, wood isn’t just low carbon, it’s carbon negative. Depending on the species of tree used, roughly 1 tonne of CO2 per cubic meter of wood is captured and stored in the frame of the house. This means each house removes several tonnes of CO2 from the atmosphere and locks it away for over 100 years.
It’s not just that a tonne of timber requires 24 times less energy to produce than steel, and captures CO2 rather than gives it off like cement (cement causes 5% of all global CO2 emissions), the fact that it is light means less energy is required to move it to the site. It also means less materials are required for the foundations, because the building is lighter. We will be sourcing all our wood as locally as possible (the planks for the exterior panels come from just over the road from our factory) and we ensure it is sustainably sourced. By situating the Citu works factory on the Climate Innovation district site we will save even more CO2 because we won’t need to use lorries to transport the finished panels to the construction site.
Why build in a factory?
By assembling the wooden panels for Citu homes in our state of the art new manufacturing facility, we can achieve a range of benefits both in terms of sustainability and for the home’s future inhabitants. By building inside rather than on a construction site we can control the process and massively reduce waste. We can ensure that construction materials are kept dry throughout the build, rather than being exposed to the elements as they would be during the normal construction process. This ensures when we add the breathable membrane that all moisture is locked out permanently, meaning the timber structure will last hundreds of years, provided it is maintained.
By having control over the process, we can improve quality, with rigorous testing for properties such as air-tightness. This will let us give our residents houses which require minimal energy to heat, as the insulation and air-tightness is so outstanding. Professor Chris Gorse’s extensive research into the design’s insulation properties found that the insulated timber walls would provide twice the insulation as a masonry wall of equivalent thickness.
Precision engineering of every component lets us cut waste by using only what is needed. Saving materials in this way means less energy is required, further reducing the building’s carbon footprint. Any off-cuts will also be burned in one of our biomass generators rather than thrown away, heating the Citu offices with carbon neutral fuel.
‘Citu's ethos is like that of leading car manufacturers, aiming to outdo the expectations of buyers with rigorous control and testing throughout the construction process’
– Chris Gorse, Professor of Construction and Project Management at Leeds Beckett University and Director of Leeds Sustainability Institute.
Durable and flexible design
We wanted to create a state of the art manufacturing facility so we could mass produce zero carbon houses. After all, one or two homes aren’t going to accelerate the transition to zero carbon cities. We needed to think big.
But what we didn’t want to do is drop buildings into cities without any concern for the surrounding area. That’s not what we’re about. That’s why we worked with Leeds Beckett University to create a housing solution that was flexible, so we could use it to build different styles of houses and apartments, specifically designed to create beautiful landscapes.
‘Citu’s masterplan for the Climate Innovation District is innovative, pushing the boundaries of what city developments can achieve’ – Chris Gorse
We also wanted our homes to last. Not just a lifetime, but several. Sustainability is all about wanting to pass on a better world to our children. So it’d be no good passing them a house that wouldn’t last. When maintained, wood is an incredibly durable construction material. Many Tudor houses in the UK are still going strong after five hundred years. But we have something the Tudor’s never did: breathable membranes which lock out moisture, keeping the timber in perfect condition so it can last for generations.
Wood is so strong that it can be used for even very tall structures. There are timber framed apartment blocks over 30 meters high, and a team at the University of Cambridge have a design for a 300-meter-high wooden skyscraper. So, there is no doubting it’s strength and versatility as a construction material.
We hope that by showing how building with wood can produce better and more sustainable buildings on a large scale, we can help create a real revolution in the industry. If adopted on a wider scale, this could help prevent the emission of billions of tonnes of CO2 every year. By sourcing sustainable timber we can also encourage afforestation, which helps to sequester billions of tonnes of CO2 from the atmosphere.
If working on building the next generation of homes to help accelerate the transition to zero carbon cities sounds like something you want to be part of, go to our careers page. We're recruiting for a wide range of positions.