Deep retrofit of a heritage community-owned pub
The Limpley Stoke Community Benefit Society (LSCBS) has succeeded in retrofitting its 16th century Wiltshire village pub, bringing it back into use, and into community ownership. The retrofit aimed to address urgent structural issues and improve the building fabric and thermal performance of the pub. The Hop Pole Inn has now reopened following the sensitive retrofit of the Grade II listed building, led by conservation architects James Sibson RIBA AABC, who led the capital works on the board for LSCBS, and Rhys Brookes RIBA AABC of Harrison Brookes.
Greengauge was part of the project team supporting the retrofit with modelling in PHPP (Passivhaus Planning Package), dynamic thermal modelling, 2D & 3D thermal bridging modelling, mechanical and electrical building services design and moisture risk analysis of internal wall insulation strategies, using WUFI modelling.
Strategy
Retrofitting a Grade II heritage building required considerable care and attention to find the right fabric and building services strategy that would work with the building. Examining the existing condition of the building and researching its construction was essential to avoid any unintended consequences from the retrofit. Greengauge carried out analysis of the building fabric and used the findings when modelling the building using PHPP to evaluate any proposed improvements. Greengauge also undertook moisture risk analysis to ensure that any proposed internal wall insulation strategies would be suitable. To find the right, proportionate solutions, the team engaged in detailed consultation with the manufacturers of natural lime based insulating plaster products and traditional plaster. Building services design undertaken by Greengauge also helped ensure the right ventilation and heating strategy for the project.
Project team
Client: Limpley Stoke Community Benefit Society
Architect: Harrison Brookes Architects
Contractor: Ken Biggs Contractors Ltd
Structural Engineer: Mann Williams
Technical product support: Amar Eco Plaster
Building physics: Greengauge
Moisture risk: Greengauge
M&E Design: Greengauge
Key data
“It’s not about whether we can, or should heat historic buildings with clean energy, or whether we can or should improve their thermal performance. It’s about thoughtful balancing of multiple competing priorities!”
Hannah Jones, Director, Greengauge
Key features
PHPP modelling
At the outset Greengauge developed a model of the existing building, using Design PH & Passivhaus Planning Package (PHPP). The first step was to geolocate the building and input values for the different variables within the building. The predicted annual energy consumption of the building was calculated, with the PHPP modelling creating a breakdown of energy consumption associated with each element of the building. From this model, Greengauge then made recommendations on how to optimise the building fabric to improve thermal comfort and energy consumption.
Moisture risk analysis
Greengauge supported the project team by undertaking moisture risk assessment of the Hop Pole Inn retrofit, using hygrothermal simulation in WUFI. When undertaking heritage retrofit projects it is crucial to understand the moisture behaviour of the whole element and use appropriate new materials and specifications that respond to the existing construction. Remedial work to keep walls dry and protected from environmental moisture is fundamental. Managing moisture generated from occupation is also essential, through good ventilation strategies; Greengauge’s role as both MEP designer and moisture risk assessor helps ensure joined-up thinking.
Greengauge undertook WUFI modelling of different proposed Internal wall insulation strategies to understand the relative risks and advise on the design of the insulation. Greengage undertook material testing of mortar and stone used in the building to inform modelling.
The modelling showed a good ventilation strategy was essential to control relative humidity and hence moisture risk, once the building was occupied and in use. The recommendations included:
- A modest layer of capillary active insulation would be appropriate.
- Occupation-generated moisture should be managed via a robust ventilation strategy.
- The envelope should be repaired and maintained to minimise rain ingress.
- U-values of around 0.5W/m2K, using appropriate materials, would mitigate the moisture risk
- An MVHR (mechanical ventilation with heat recovery) system should be installed, to ensure proper ventilation throughout.
Insulation & airtightness strategies
Four different insulating plaster approaches were specified for different elevations to provide the internal wall insulation strategy for the project. Greengauge worked closely with the architects to ensure continuity of insulation and minimising thermal bridging, for example installing replacement windows within the insulation zone. The overall target for heating energy requirement
was an impressive 60 kWh/m2/year, a vast improvement from the 300+ kwh/m2/year of the pre-retrofit building (as modelled in PHPP).
Building services
As well as designing an MVHR system for the pub, Greengauge also encouraged the pub to switch heating supply to an air source heat pump (ASHP). The fabric and ventilation improvements significantly reduce the size and cost of an efficient ASHP system, as well as the running costs.
ASHPs can be installed into buildings with high heat demand, but both the heat pump itself, and the distribution system must be physically larger, to achieve sufficient heat output at peak load, and efficient operation via low distribution temperatures.
The ventilation demands of a commercial kitchen presented a particular challenge. Good practice ventilation means very substantial plant, and large heat losses during operation. The heat losses are offset by heat gains from the appliances, and Greengauge was able to advise on appropriate strategies to ensure comfort and efficiency as well as compliance with the relevant standards and regulations. To simplify the services strategy, the kitchen was treated as a separate entity and contained in a new extension.
In use
The Hop Pole Inn re-opened in January 2025 and has already been a huge success, recently being rated in the Good Food Guide’s Top 100 pubs.
The building systems have worked well providing year round comfort, without excessive complexity. At its heart is an awareness of ventilation to reduce moisture ensuring improved comfort. The buildings historic 16th century construction of stone and earth mortar required an approach that understood the building’s inherent behaviour, aligning the solution with its host.
James Sibson, Conservation Architect
