A greener way to retrofit?

The Global North must do more to retrofit its existing building stock to reach net-zero targets by 2050. This was one of the messages to emerge from COP27 in Sharm El-Sheikh in November. Timber and timber products can be a useful part of the retrofit toolkit, offering benefits that include lighter structures, lower embodied carbon and a boost to wellbeing.

Slow build

Renovating buildings at a rate of over 2% a year is crucial for developed countries if they are to hit decarbonisation targets. A September 2022 report from the International Energy Agency estimates that at least 40% of the floor area of buildings in developed countries was built before 1980, and that 20% of buildings must be retrofitted by 2030 to reach carbon reduction milestones.

With many of the UK’s buildings dating considerably further back than the 1980s, there is much work to do in both the commercial and domestic sectors. A report last year from Jones Lang Lasalle, suggested that 90% of office stock in England and Wales’ largest regional office markets were at risk of not meeting the Government’s goal of an Energy Performance Certificate (EPC) rating of B by 2030.

Industry bodies continue to pressurise the Government to adopt a National Retrofit Strategy to improve the energy efficiency of the majority of the UK’s existing 28 million homes. The Construction Leadership Council published its second version of the National Retrofit Strategy in June last year, calling for a systematic approach over a 20-year period to 2040.

Retrofit is ramping up slowly in the social housing sector, where landlords must bring stock up to EPC level C by 2030. November saw the deadline for applications to the latest £800m wave of the Government’s Social Housing Decarbonisation Fund for installing energy performance improvement measures in social homes in England.

In the commercial sector, private companies are driving action. Property owners such as Grosvenor report that high-end occupiers are looking at both operational and embodied carbon when considering new tenancies. Grosvenor is spending £90m to update its portfolio to drastically improve energy efficiency.

Marks & Spencer’s controversial plans to demolish and rebuild its flagship Oxford Street store have energised the conversation about retrofit. During the public inquiry into the proposed project, Tyler Goodwin, CEO of London developer and investor Seaforth Land warned that companies would lose customers if they did not develop responsibly:

“Our industry must do more now to reduce our whole-life carbon in developments,” he said. “That doesn’t mean stopping development, but it does mean trying harder first to retain, reuse and adapt what we have.”

What timber products can be used in retrofit projects?

There are a multitude of timber products that can be deployed in retrofit projects, some more obvious than others.

At the larger end of the scale engineered timber such as cross-laminated timber (CLT) can offer an efficient alternative to traditional construction types. Developers are deploying structural timber frames to extend existing buildings upwards on projects such as Technique in Clerkenwell, where two existing buildings were stitched together and extended by three floors using CLT and glulam. This solution saved around 40% of carbon compared to a steel structure and 48% compared to a concrete one.

At the Old Gramophone Works in Kensal Rise, London, two storeys became six, with a hybrid CLT and glulam frame added onto the existing reinforced concrete structure to create this workspace for creative SMEs. Studio RHE worked with structural engineer Heyne Tillett Steel to deploy an engineered timber structure so that minimal reinforcements to the existing foundations were required.

Aside from their lower embodied carbon and lighter weight, structural timber frames such as these can bring logistics and programme benefits too. With offsite manufacture, fewer resources are required on site and fewer lorry movements; time on site can be lessened with less disruption to neighbours and businesses.

The winner of the 2022 AJ Retrofit of the Year award for workplace projects under £5m shows how timber can deliver benefits on a smaller scale. When Heyne Tillett Steel wrote the brief for its own office at 16 Chart Street in East London, low carbon was high on the ask list. The transformation of this 1930s warehouse, with Ian Chalk Architects, deploys a panellised timber system to add a storey to the building, an extension to the side, and a new stair and lift core.

On an even smaller scale, architecture for london retrofitted an Edwardian terraced house in Muswell Hill, to show how a ‘low energy’ retrofit within a constrained budget could work. Both embodied and operational energy had to be low, with a timber structure and wood fibre insulation deployed alongside triple glazing, insulation and high levels of airtightness.

With PassivHaus-level developments on the rise, particularly in the social housing sector, specialist timber-based products to serve this market are becoming more readily available. For instance, there are structural OSBs with an integrated vapour control layer that help meet the high air tightness requirements for PassivHaus standard homes.

Woodfibre insulation, though not widely used yet, is specified where embodied carbon, natural products or the avoidance of volatile organic compounds (VOCs) are high on the agenda. There are also more standard timber products that can be installed as part of the retrofit mix: energy efficient timber-framed windows, timber doors, sub-floor base material, timber flooring and interior wood cladding. OSB and chipboard can be used to board over insulated lofts.

Natural products were a must for the owners of a private 1920s mansion apartment in Ealing who chose sustainability and health specialists Grigoriou Interiors for their renovation project, with a brief to use high-quality natural products and to minimise negative environmental impacts. Among the more unusual timber products used was Fermacell wallboards due to their carbon, environmental and durability credentials. Timber was used extensively, including for windows and doors, the kitchen worktop and cabinets, bedroom and bathroom joinery, cupboards and a walk-in wardrobe.

Retrofiting Healthier 

Technical and carbon considerations aside, timber elements are often chosen for retrofits and refurbishments because of their biophilic benefits. Studies have shown that timber used internally, with its grain visible, has positive impacts on a building’s inhabitants or users: heart rates and stress levels fall and, in working environments, productivity rises.

Connections with nature were designed into the redevelopment at Republic at East India Dock in London’s Docklands. Now light and airy and benefitting from timber framed extensions to their space, the two late 1980s and early 1990s reinforced concrete office blocks are linked by a pedestrian outdoor space with water features, planting and timber pavilions.

BDP has designed in the calming effects of timber to the retrofit of an office building which will become the Bristol University Dental School. The effect of timber surfaces and a living green walls in the atrium will perhaps lessen the terror of those visiting the school.

Oliver Heath deployed biophilic principles on the re-design of a family house in Bergen in Norway. Small windows were enlarged to provide views across the fjords and natural light. The interior is both bright and soothing with light-coloured pine flooring and cladding on the chimney breast and pine storage and seating spaces.

In conclusion

The imperative to both re-use older buildings and to upgrade their energy efficiency means that the next decade should see a significant increase in retrofit projects. Sustainable retrofit strategies must encompass responsible use of resources, embodied carbon as well as operational carbon and the impact of design and material choices on health and wellbeing.