11 and 19 Passmore Street are the first privately rented buildings in London to achieve the EnerPHit Passivhaus standard. Developed by Grosvenor Britain & Ireland, the refurbished properties give customers the best of both worlds – the appeal of a period home at a quality above new build. Building on the success of this project, Grosvenor is already upgrading more buildings to the EnerPHit Passivhaus standard.
Excellent thermal performance and sound insulation
Clean air, with ducts filtering 80% of large dust particles
£900 annual energy cost savings for occupiers
804 tonnes less CO2 over the lifespan of the buildings
Passivhaus Award 2015
Grosvenor, an international private property group, works in some of the most dynamic cities around the globe. Guided by their ‘Living cities’ philosophy, the team strives to create, manage and invest in properties and places that contribute to the enduring success of cities.
11 and 19 Passmore Street are historic 1860s terraced houses, situated in a conservation area in Belgravia, Westminster. They were identified as pilot projects to support Grosvenor’s commitment to reduce CO2 emissions by 50% across its directly managed London estate portfolio by 2023.
This project also offered Grosvenor the opportunity to test the EnerPHit Passivhaus standard in period homes, focusing on building fabric, energy efficiency, comfort and indoor air quality. Grosvenor owns many period properties in London and seeks to conserve historic fabric, while delivering homes for customers that are fit for purpose, sustainable and a pleasure to inhabit.
The project team included Sturgis Carbon Profiling (architect and Passivhaus consultant), Edward Pearce (mechanical and electrical consultant), Grangewood (contractor), Hurst Peirce + Malcolm (structural engineer) and CoCreate (Passivhaus certifier).
Construction began in March 2014 and completed in January 2015. Both properties were occupied in February 2015.
Insulation and air tightness measures included:
Additional Passivhaus measures included:
How to get team buy-in for Passivhaus?
This was the first time Grosvenor, Grangewood or Sturgis had delivered a Passivhaus project, and so team training was key to success. The whole team visited the Target Zero Passivhaus training centre in Ireland before work began on site. Sturgis also provided extensive training on air tightness and other Passivhaus concepts to the builders and subcontractors, such as electricians and plumbers. In addition, Grosvenor partnered with Grangewood, the company’s preferred builder for domestic retrofits, rather than using a normal competitive tender, with the entire team focused on Passivhaus from the outset.
How to locate and fix air leaks in period homes?
Grosvenor recommends air testing below 50 air changes per hour (ach) until the air tightness membrane is covered, to avoid damage due to over-pressure. At 11 Passmore Street, continuous air testing at high pressure during building works caused delays as membranes were pulled apart at taped joints. The detailed air tightness work to locate and fix air leaks contributed to the preliminary phase taking longer than expected. The team carried over lessons to 19 Passmore Street, speeding up the process. The first air tightness test at No 11 came in at around 6ach, and it took two more weeks of sealing to get it down to 0.8. Whereas, the first test at No 19 came in at 1.2ach, and it took just one day’s work to get down to 0.9, within the Passivhaus target of 1.0.
How to avoid causing condensation when insulating historic buildings?
Internal insulation can create a ‘dew point’ between the new insulation and the old wall, where the temperature drops and water vapour condenses to liquid, potentially leading to mould. At 11 and 19 Passmore Street, the team stripped back the fabric and carried out masonry repairs to ensure all brickwork was in good condition. Then they applied aerogel insulation, a highly insulating, breathable material to further reduce the risk of condensation. Sturgis also designed out thermal bridges, points where cold structures penetrate the insulation layer, to eliminate possible dew points. They prepared 26 individual thermal bridging details and carried out 3D thermal modelling of the building's steel supports. In addition, the front façades at 11 and 19 Passmore Street are rendered, which helps prevent rain and moisture getting into the building fabric.
Retrofit Project Manager
Grosvenor Britain & Ireland
Dylan Pritchard, Building Surveyor at Grosvenor
“I lived there in February for one week. I felt refreshed and full of energy in the mornings because of the filtered fresh air. The weather was also very cold that week, so it was an ideal testing ground and the triple glazing really made a difference. It was extremely quiet and that, together with the ventilation, made for a great, healthy living experience.”