sustainable renovation at John Gilbert Architects

Over the past 10 years, John Gilbert Architects (JGA) has invested in upskilling 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 Passivhaus consultancy.

Clients, primarily those interested in retrofit, approach JGA because they want to understand how their buildings perform and want precise recommendations of how 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 housing association movement, which included tenement rehabilitation in Glasgow’s most deprived areas, often basics such as fitting indoor toilets.

In 1993, Gilbert co-authored The Tenement Handbook: A Practical Guide to Living in a Tenement. From the outset, his approach to housing 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 housing, 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, who joined the practice in 2004, explains: ‘We got quite heavily into how our buildings were performing, because we wanted to reduce fuel poverty.’

Source:Tom Manley

Block 2, Canongate

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 School of Art’s Mackintosh Environmental Architecture Research Unit (MEARU) provided a starting point and, in 2015, architect and building performance specialist Barbara Lantschner joined the practice to lead a Knowledge Transfer Partnership (KTP) jointly with MEARU, monitoring the performance of the stock of five housing associations 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).

‘Have a plan that looks at the fabric first’

I think the fabric-first approach can be implemented to the majority of archetypes. The idea is not to insulate every single element, but to reduce space heating demand as far as you can by focusing on the main issue to improve the fabric for each archetype.
So it might be that, for a historic building, you only have to focus on the air tightness and for other buildings you have to focus on the floors or the walls. Or you can do it all from the outside, without disturbing tenants. Or you do it from the inside, because you’re in a conservation area. The point is to have a plan that looks at the fabric first and pick out the elements that will make the biggest impact. After that, you work on the active systems, such as heat pumps or renewables. The principle is – from a sequence point of view – to look at fabric first. And if that’s not possible, continue with the rest.
Barbara Lantschner, associate director and building performance specialist, JGA

A hard-nosed look at how 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 housing association in lieu of traditional fees. Quarterly workshops were held at which all participants 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 analysed 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 how 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 housing types, Lantschner explains that the definition of what comprises ‘an archetype’ is ongoing, as well as how 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 without the practice’s ongoing involvement.

Source:Tom Manley

Niddrie Road

The uptake of Passivhaus 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 Passivhaus approach to retrofit, is not realistic for every archetype. While it may be appropriate for a semi-detached house 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.

Source:John Gilbert Architects

Wick Enerphit

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 Passivhaus into Scottish regulations, including the embodied 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 without losing its focus on tenants and fuel poverty. Today, four of its 20 staff 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 attitude 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.

Case study 1: Block 2, Canongate, Edinburgh

Constructed in 1969 to a design by Sir Basil Spence, Glover and Ferguson, the project focused on Block 2 of this Category B-listed building  within the Edinburgh World Heritage Site, consisting of 12 residential and two commercial units. The original concrete frame and uninsulated cavity brick and stone wall construction had developed numerous problems, including spalling concrete, failing render and surface condensation, together with high levels of asbestos, poor indoor air quality and mould growth. The owners of the block formed a client group with support from Edinburgh World Heritage Trust, and funding came from two energy efficiency funds and a conservation funding programme, as well as owners’ contributions. The results have seen the architectural significance of the building enhanced, environmental issues mitigated and energy bills reduced, with operational carbon emissions of the building falling by 46 per cent. Post-occupancy evaluation is currently under way and future phases on neighbouring blocks are planned.

Photograph: Tom Manley

Location 79-121 Canongate, Edinburgh | Client Block owners with Edinburgh World Heritage Trust | Cost £700,000 | Start on site March 2020 | Completion March 2021 | Total primary energy 125.5 kWh/m²/yr | Carbon emissions (all) 894 kgCO2/m² | Airtightness at 50Pa 3.5 m³/hr/m² | Overall thermal bridging heat transfer coefficient (Y-value) 0.2 W/m²K | Overall area-weighted U-value 0.57 W/m²K | Predicted design life 60 years


Case study 2: 107 Niddrie Road, Glasgow

For this decarbonisation project, eight one-bedroom flats in a pre-1919 red sandstone tenement in Govanhill were upgraded to EnerPHit standard and retrofitted to achieve ultra-high levels of insulation and airtightness. New heating and ventilation systems were installed. Since this is the first time this had been attempted on a sandstone tenement in Scotland, an ongoing follow-up research project is being conducted by Strathclyde University, using data from moisture monitors installed at key points in the building fabric during construction, and monitoring equipment attached to MVHRs, WWHR units, electric meters and gas meters tracking energy usage. This has demonstrated that the project has drastically reduced energy bills for the tenants while providing them with a more comfortable and healthy internal environment.

Photograph: Tom Manley

Location Govanhill, Glasgow | Client Southside Housing Association | Cost £1.14 million | Start on site N/A | Completion October 2022 | Heating load 16 W/m² | Heating demand 22.5 kWh/m²/yr | Carbon emissions (all) 792 kgCO2/m² | Airtightness at 50Pa 4.3 m³/hr/m² | Overall thermal bridging heat transfer coefficient (Y-value) 0.019 W/m²K | Overall area-weighted U-value 0.183 W/m²K | Predicted design life 60 years


Case study 3: Wick EnerPHits, Caithness

This project saw the retrofit of two post-war houses in Wick, Caithness to EnerPHit standard. The two houses had the highest levels of insulation installed, rendering traditional central heating unnecessary and elevating their Energy Performance Certificate rating from F to A. Their air permeability is now below 1 m³/h/m² @50Pa – a first for a Scottish social landlord. This was a pilot study, aiming to explore the feasibility, costs and practicalities of implementing the EnerPHit standard in social housing and to provide a model for other affordable and social housing providers. It was enabled through the Scottish Government Net Zero Heat Fund and John Gilbert Architects worked together with Hardies Consultant, Changeworks and local contractor GMR Henderson. The houses are currently under review for Passivhaus certification.

Photograph: John Gilbert Architects

Location Wick, Caithness | Client Cairn Housing Association | Cost Undisclosed | Completion 2023 | On-site energy generation (in relation to projected building footprint area) 70 kWh/m²/yr | Heating load 14 W/m² | Heating demand 27 kWh/m²/yr | Carbon emissions 644 kgCO2/m² | Airtightness at 50Pa (average post-installation) 0.8 m³/hr/m² | Overall thermal bridging heat transfer coefficient (Y-value) 0.022 W/m²K | Overall area-weighted U-value 0.135 W/m²K | Predicted design life 60 years