Passivhaus Affiliate

Estate-wide EnerPHit-informed retrofit planning

A pilot retrofit scheme for PHT Patron City of Edinburgh Council aims to inform its approach to 400 non-residential buildings in its estate and offers potential lessons for other local authorities. The Council's ‘EnerPHit Informed Retrofit Plan (EiRP)’ uses a bespoke framework and technical analysis established by PHT Patron Architype to assess the initial pilot buildings, comprising mainly offices and educational buildings.

City of Edinburgh Council EiRP rertrofit plan. Image credit: Architype

The EiRP process involves:

  • Accurately calculating energy consumption and carbon emissions
  • Estimating running cost and capital cost impacts
  • Illustrating a series of options from ‘Do nothing’ to full EnerPHit – for all or part of a wider estate
  • Enabling comparisons between building types and across estates
  • Supporting decisions about the appropriate level of intervention
  • Ensuring informed planning of immediate interventions and future facility management/upgrades


The brief

City of Edinburgh Council (CEC) has an ambitious target of net zero carbon in operation by 2030 and is keen to understand the optimal pathway for its built assets. The council is already aware of the effectiveness of Passivhaus and is rolling out newbuilds to the Passivhaus standard. However, when it comes to retrofit, there was a need for the council to be able to understand the level of additional capital expenditure when going beyond minimal interventions. CEC’s key criteria for its retrofit programme include:

  • Cost: understanding the implications of moving buildings onto low zero primary plant solutions like heat pumps.
  • Carbon reduction: tackling the climate emergency as well as reducing extra demands on the national grid, as the local grid infrastructure is close to capacity.
  • Health & well-being: delivering healthy buildings, with indoor air quality in focus since the COVID pandemic.
  • Heritage value: balancing the needs of retrofit with the heritage value of many of the city’s buildings.


Stage 1: Overview of the whole estate

The first stage of the EiRP involved working with CEC’s asset management team to establish the types of construction and eras of construction of the 400 heated buildings in the estate. The portfolio includes buildings spanning many uses, construction typologies, ages, storey heights, and levels of architectural value.  From the whole estate, 12 buildings were selected that were felt to be representative of all the building types in the estate. Of these, two buildings were selected for a detailed deep-dive case study:

  • A Victorian Villa operating as a Nursery, situated in a conservation area and suitable for an internal wall insulation strategy

  • A Primary School, built in the 1960s and suitable for an external wall insulation strategy

Step 2: Detailed modelling

The team led by Architype then started to examine the buildings in detail and the buildings’ existing states were modelled and verified against existing energy meter data.

The analysis was grounded to the physics of the estate using 12 typical buildings that were forensically analysed as case studies. The structures were fully modelled from 3D point-cloud surveys, tested for airtightness via blower-door tests, analysed for cold-bridging using thermographic imagery, and physically opened-up (where allowable) to better understand their material construction. Whilst it is clear that 12 buildings cannot represent all atypical abnormal building typologies, the 12, chosen in conjunction with the Councils Asset Management Team, were reflective of the main typologies and building characteristics most common within the estate

Seb Laan Lomas, Associate and Passivhaus designer, Architype


Step 3: Developing intervention options

A range of different intervention scenarios were identified:

  • Option 1: No fabric improvements, only heat pump installation measures to support decarbonisation.
  • Options 2-3: Middle-of-the-road options, often including MEV ventilation and more relaxed airtightness.
  • Option 4:  Fully certified EnerPHit standard (often using the component method, with certain exemptions allowed based on the heritage value).

Creating a variety of interventions was a useful part of the process and helped to identify certain options that immediately appeared impractical.

City of Edinburgh Council EiRP rertrofit plan. Image credit: Architype


Step 4: Costing the scenarios

Before deciding which scenario to go for, each option was costed with the key condition information in mind for retrofit purposes. Complexity around phasing and de-canting was not part of the study so it is understood that these would be developed at the relevant RIBA stages. This was mapped alongside predicted annual operational costs for over 30 years.


Step 5: Establishing a decision-making process

During the establishment of the EiRP, CEC held weekly meetings with Architype. These regular meetings were a core part of understanding CEC’s decision-making processes, priorities, and pressures. They worked together to establish a work-in-progress Total Performance Index mechanism to help with decision-making to compare the projects weighted according to the different priorities of cost, carbon, health and well-being, and heritage value. The Total Performance Index tool worked as an initial benchmark for making the significant decisions as to where the Council should best invest its money.


Step 6: Extrapolating across the whole estate

After the two initial pilot projects, the team is continuing to develop retrofit strategies for the other initial ten buildings and drawing conclusions from those processes for the wider estate, using the Total Performance Index.  The characteristics of each building in the estate significantly influence the energy measures implemented. If the retrofit programme was rolled out over the entire estate of 400 buildings, the average energy savings would be an approximate improvement of 61%, but varied considerably according to building type and the optimal measures.

The data points of the 12 case studies were extrapolated across the estates’ 400+ buildings to provide answers to how many buildings required which level of intervention to hit the council’s carbon target, and how much it would cost. Importantly this data also illustrated the projected aggregated financial saving from the operational improvements across the estate alongside a projected capital expenditure for the council to carry out the works including for optimism bias within the capital projections. This provided a technical backdrop to wider council discussions around the remit of achieving net zero carbon by 2030 and 2045 key targets in the council’s climate policy agenda.

Anna Kerrane, Architect, Architype 

Retrofit or newbuild?

A key question for CEC and the design team when deciding how to retrofit an estate was whether to enhance an existing building, or replace it with a new build. Architype’s Perform+ consultancy team addressed this by undertaking a lifecycle analysis of the intervention options using its ECCOLAB software that illustrated that EnerPHit-level interventions would result in lower whole-life carbon emissions than a new build. However, wider considerations beyond just the building condition need to be managed by large public sector clients, these conclusions inform part of a wider asset management planning within the council’s education estate. This is still a work in progress with the council as part of their wider investigations into achieving a net zero carbon estate.

Lessons learned

The EiRP is beginning to be rolled out and is progressing, starting with a selection of the initial 12 buildings, which will all be carefully monitored. The first three buildings in the programme are aiming for either the EnerPHit or the AECB Retrofit standard. Initial findings and conclusions for the Architype-led team include:

  • An EiRP enables an informed decision for each building about what level of upgrade is appropriate and affordable, or if another asset management decision is required for that property
  • Only upgrading MEP (eg installing a heat pump) creates comfort issues, brings significant practical challenges, and increases running costs. It would also have wider implications on grid capacity, and create stranded assets/carbon lock-in.
  • A ‘no regrets approach’ embraces energy reduction and fabric improvement, regardless of the heating technology deployed.
  • Reducing energy consumption is an essential part of meeting Scottish and other carbon targets and supporting grid decarbonization and capacity challenges.


One finding from this co-ordinated analysis was that switching existing buildings to air source heat pump technology without doing significant fabric improvements would result in an unrealistically large number of additional radiators and increased energy costs of up to 60%, and that was with last autumns’ energy figures. The costs could be as high as 150% given projections for this winter.

Mariam Kapsali, Architect & Passivhaus Designer, Architype

UK Passivhaus Conference 2022

The City of Edinburgh Council’s EiRP will be discussed in greater depth during the UK Passivhaus Conference 2022 on 26 October 2022. Discover more about Passivhaus Retrofit in the UK in our research report, setting out how EnerPHit fits into the wider net-zero retrofit agenda.


Further Information

How to achieve zero carbon estates 

Passivhaus Retrofit

PHT research report: Passivhaus Retrofit in the UK - 2022

Passivhaus Educational Buildings

Passivhaus Social

Previous PHT story: Renfrewshire retrofit programme aims for EnerPHit 20 June 2022

Previous PHT story: Local Passivhaus policies 6 May 2022

Previous PHT story:  Scottish Schools lead large scale Passivhaus  8 April 2022

Previous PHT story: Scottish Secondary strives for Passivhaus first – 11 March 2021

1st August 2022

Never miss UK Passivhaus news by joining the Passivhaus Trust mailing list Follow us on twitter @PassivhausTrust

< Back To News