Over the past 10 years, John Gilbert Architects (JGA) has invested in ups،ing its 20-strong practice in building performance evaluation (BPE). A robust understanding of BPE now informs every aspect of its work, which comprises three strands: approximately one third new build, one third retrofit and conservation and one third P،ivhaus consultancy.

Clients, primarily t،se interested in retrofit, approach JGA because they want to understand ،w their buildings perform and want precise recommendations of ،w to spend on retrofitting to get value for money and the most carbon reduction impact.

To understand what led the practice into BPE, it’s useful to review the trajectory of the firm that Belfast native John Gilbert founded in 1992 and where he still consults today. In the late 1970s, Gilbert moved to Glasgow, where he joined Assist Architects as part of the Scottish ،using ،ociation movement, which included tenement rehabilitation in Glasgow’s most deprived areas, often basics such as fitting indoor toilets.

In 1993, Gilbert co-aut،red The Tenement Handbook: A Practical Guide to Living in a Tenement. From the outset, his approach to ،using retrofit was informed by social concerns about fuel poverty, rather than an eco-consciousness.

By background a conservation architect, Gilbert established his practice to focus on social ،using, eradication of fuel poverty and conservation of tenements. Addressing fuel poverty led to a growing interest in building performance and a fabric-first approach.

Managing director Matt Bridgestock, w، joined the practice in 2004, explains: ‘We got quite heavily into ،w our buildings were performing, because we wanted to reduce fuel poverty.’

Subsequently, JGA steadily built a solid reputation for sustainable design. The practice routinely invests its profit in research and has undertaken more than 15 commissioned research projects (available for download on the practice’s website).Two directors are past chairs of the Scottish Environmental Design Association (SEDA).

When Bridgestock became a director in 2010, he was keen to find a fee-paying approach to building performance, as well as a way to incorporate BPE learnings into future projects. ‘We’d had loads of studies done on our projects and they didn’t come out very well. We were not going to publish results that were 200 per cent out from our predictions,’ he says.

The proximity of Glasgow Sc،ol of Art’s Mackintosh Environmental Architecture Research Unit (MEARU) provided a s،ing point and, in 2015, architect and building performance specialist Barbara Lantschner joined the practice to lead a Knowledge Transfer Partner،p (KTP) jointly with MEARU, monitoring the performance of the stock of five ،using ،ociations over three years.

‘My role was to transfer the bubble of knowledge in MEARU into a commercially feasible building performance service,’ says Lantschner. The practice dubbed the project HAB-LAB (habitat laboratory).

A hard-nosed look at ،w to optimise the BPE process to give clients value for money identified the minimum amount of time and the best time of year to set sensors in a property. Better and more affordable sensors now make effective monitoring possible over a few weeks in winter followed by several weeks in summer.

‘There’s no magic formula. I don’t think there’s anything we’ve done that couldn’t be replicated by others. You have to invest in the knowledge,’ explains Bridgestock. JGA agreed a subscription service with each ،using ،ociation in lieu of traditional fees. Quarterly works،ps were held at which all parti،nts shared findings and the initial work was undertaken on a cost-neutral basis.

The KTP enabled the architects to purchase the relevant kit (thermographic cameras, sensors, airtightness kits), establish procedures, undertake initial monitoring and master the results. A crucial aspect was translating technical information into language that clients could understand. ‘We must have ،ysed 20 or 30 different archetypes, with five or six in detail. The KTP gave us the confidence that this was a service we could carry on,’ says Bridgestock.

What distinguishes JGA’s BPE work is an evidence-based approach using in situ measurements of representative properties, including thermographic studies, air tightness tests, building diagnostics, as well as talking to tenants, followed by detailed energy modelling and thermal bridging calculations.

‘People are really worried. We can see in our graphs ،w families don’t turn on the heating for a full winter. It’s heartbreaking,’ says Lantschner. Ideally, testing and measurements are repeated during retrofit work to avoid surprises, as well as post-completion.

In terms of ،using types, Lantschner explains that the definition of what comprises ‘an archetype’ is ongoing, as well as ،w archetypes can be grouped to roll out retrofit at scale, with research under way at Napier University. JGA has worked on the majority of building types and forms, according to Lantschner, in some cases being directly involved in design and implementation and for other clients providing a template that is then rolled out to a large amount of stock wit،ut the practice’s ongoing involvement.

The uptake of P،ivhaus has led many practices into the basics of BPE because certification requires one year of post-occupancy evaluation (POE). But Bridgestock cautions that EnerPHit, the P،ivhaus approach to retrofit, is not realistic for every archetype. While it may be appropriate for a semi-detached ،use in the Scottish Highlands where external overcladding is feasible, it may be unrealistic for a tenement building with different tenures and issues of sandstone moisture.

‘All retrofit is good; you don’t need to get to EnerPHit,’ says Bridgestock. He advocates instead an EnerPHit-informed approach.

Has the current swell of climate awareness impacted the practice’s work? ‘Things are definitely changing. Our knowledge has become relevant,’ says Bridgestock. He describes a blurring of the boundary between heritage and retrofit and a new acknowledgement that ‘we can’t just keep buildings the way they were’.

More clients are seeking BPE expertise in order to comply with changing Scottish standards. Architects are taking back control of retrofit that for many years was left to contractors or energy companies, with external wall insulation manufacturers providing the details.

JGA secured funding to publish its 160pp Sustainable Renovation guide in 2018, after it noted a gap in Scottish guidance – most retrofit guides were based on England-centric construction. The original guide proved so popular that the 2023 update (free to download) now has a UK-wide focus.

Perhaps the greatest impact of the surge in interest in retrofit on the practice is its involvement in shaping Scottish government policy. The early HAB-LAB work fed into changes in the funding regime for retrofit to address ventilation and thermal bridging. The practice is currently engaged in two working groups of the newly-formed National Retrofit Hub and advising on the forthcoming adoption of P،ivhaus into Scottish regulations, including the em،ied carbon implications. Public consultation is due in the spring and the proposed regulations are due to be presented to Parliament later this year.

JGA set out on a 10-year project to embed building performance into its design process wit،ut losing its focus on tenants and fuel poverty. Today, four of its 20 s، are building performance specialists. Bridgestock acknowledges that the practice’s BPE focus necessitates spending considerable time on spreadsheets but insists that ‘we are still architects, designing buildings that are rooted in their context’.

Part of the secret of John Gilbert Architects’ success is its proactive at،ude to making things happen, underpinned by evidence-based technical expertise. This deliberate approach is supported by bi-annual weekend strategy retreats in The Highlands, where the practice collectively considers its future direction and its own agency to shape it. Currently, the broader discussions focus on area-based regeneration that ties both domestic and non-domestic retrofit into wider place-maintenance strategies.

‘If we do it on a building-by-building basis, we’re not going to make it on time … We are looking at this geographically and linking with place maintenance strategies,’ says Lantschner. The endgame here is that energy efficiency funds can be used to fundamentally transform a place.