The environmental crisis has prompted the construction industry to focus on improving the energy efficiency of new builds to mitigate climate change, most often by reducing reliance on fossil fuels.
However, a second school of thought is focussed on the carbon footprint arising from the construction process itself.
Carl Elefante famously coined the phrase “The greenest building is one that already exists.” This insight is important because preserving and adapting existing structures will significantly reduce carbon emissions, avoiding the environmental impacts associated with new construction.
When it comes to retrofitting existing structures sustainably, wood should be top of the list, according to Professor Robert Hairstans at Edinburgh Napier University. (ENU).
Robert is also the founding Director of the Centre for Advanced Timber Technologies (CATT) at the New Model Institute of Technology and Engineering (NMITE in Hereford). In short, he knows about wood.
When he decided to renovate his 1950s bungalow in Edinburgh, he took his expertise home with him.
- Why is retrofitting so important and what challenges did you face?
“So much focus is on new builds and Passivhaus standards, but from a sustainability perspective these efforts are a drop in the ocean. It’s existing buildings which have the most significant impact on the environment.
“However, retrofitting requires skilful integration of new elements with the existing structure, which can have implications for overall operational efficiency. In contrast, new builds have the advantage of starting from scratch, which is attractive because it makes the overall design and build process easier.
“To address this challenge, ENU has partnered with NMITE and Timber Development UK to establish a competency framework sector and series of short courses. We have also launched a Transforming Timber platform to encourage the use of timber and other biogenic approaches for construction delivery. This includes restoration and refurbishment.
- Which timber products/ technology did you use – and why?
“In addition to a standard attic conversion we completed three separate extensions, each with a different timber technology requirement.
The Sunroom (2014)
“ A lightweight and well-insulated timber frame ’closed panel’ system – manufactured off-site – was installed on upgraded foundations. The exterior was clad with a special type of treated Scots pine manufactured by Accsys Technologies called ‘Accoya’, which enhances durability and resists decay.
Dining / Living Area (2014)
“The second glazed extension is cantilevered out, so didn’t require new foundations: the design was tailored to the existing structure’s support. We used Accoya treated – acetylated – wood for the glulam support beams and frame as it is renowned for dimensional stability. Imported resource was used, given the need for a species that offered the structural characteristics required for the cantilever. This approach offers longevity and resistance to movement, which is essential for glazing components.
Kitchen / Utility and Office (2022)
“The third, large extension coincided with ENU and partners launching the Transforming Timber project. That influenced my decision to pursue a ‘mass timber’ approach as it offered notable advantages. The ability to pre-fabricate panels offsite at innovation centre Built Environment – Smarter Transformation by EcoSystems Technologies, allowed for efficient installation of windows and doors supplied by Velux and Dornoch-based Tree Craft; external zinc cladding supplied and fitted by HL Metals, and other components such as the wood fibre insulation. Installing the prefabricated panels was completed in two days demonstrating the speed and convenience of a mass timber approach.
- How has this retrofit improved your EPC and your overall environmental impact?
“The original EPC for the house was E53. The initial work brought this up to B82. However, this was prior to our most recent extension, which is insulated to near Passivhaus standards, plus the re-rendering of the existing house in Corksol, a biogenic rendering, and the implementation of a Sunamp thermal battery for hot water. We are yet to obtain our new EPC rating, but we must have an A rating now.
“Overall, the mass timber extension achieved a net carbon benefit of -2,138 kg CO2 equivalent.
“For the extension as a standalone entity, we estimate it will take 26 years before there is any likelihood of a negative environmental impact. By then the national grid should be fully decarbonised.
- What would you like the future to look like for timber construction?
“Here’s my elevator pitch! When trees grow, they absorb carbon dioxide and store it. When timber is used to make engineered wood products like cross laminated timber, it can store around 676 kilograms of carbon dioxide per cubic metre. Additionally, using wood fibre insulation can further lock away carbon whilst providing the building with a breathable, external fabric.
“But practicalities are important. Anyone planning a retrofit must factor in kit and logistics from the beginning, tailored to the building typology.
“Engaging architects with the knowledge to specify and design with modern timber products is crucial. We worked with David Blaikie Architects and Grigor Mitchell Architect on the 2023 project, as we were collaborating on other research interests at the time.
“It’s essential that the comfort in our own homes isn’t compromised. Evidence that timber products provide higher levels of insulation can be seen from Building Research Solutions’ analysis on the energy performance of our bungalow; the floor area more than doubled, and yet heating demand decreased significantly.
“This dual benefit of reducing environmental impact and enhancing energy efficiency makes timber-based solutions my top choice for improving the built environment.”
