Situation

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).

Actions

Construction began in March 2014 and completed in January 2015. Both properties were occupied in February 2015.

Insulation and air tightness measures included:

• Efficient, breathable aerogel internal insulation to the front (0.16 U value).
• EPS external wall insulation with brick slips to rear (0.11 U value), applied to the whole street of 12 terraced houses, with additional PIR insulation applied internally to the two Passivhaus buildings.
• Mineral wool and PIR board on the roof (0.10 U value) and internally where moisture risks were low to reduce costs.
• Triple glazed, mock-sash timber windows to the front, which open inwards so they can be made airtight (1.18 U value) and triple glazed casement windows to the rear (0.68 U value).

Additional Passivhaus measures included:

• Mechanical ventilation with heat recovery (MVHR), with air ducts that filter 80% of large dust particles.
• 12 photovoltaic roof panels to generate clean power.
• Full monitoring equipment, including internal and external temperatures, relative humidity, CO₂ sensors, electricity sub-metering, heat flux meters on heating and on domestic hot water pipework.

Financials

• Project costs: 17%-19% higher than a typical refurbishment for this pilot project. However, Grosvenor estimates that the premium for retrofitting historic buildings to Passivhaus standard will ultimately be reduced to 5%, as project teams become more experienced.
• Rental premium: none currently, but as consumers become aware of the benefits of Passivhaus, in terms of comfort, health and energy bills, the standard should contribute to a rental premium and reduced voids.
• Energy savings: £900 estimated annual saving for occupiers.

Benefit

• High comfort levels, with excellent thermal performance and sound insulation, clean air, a consistent temperature and no draughts, so occupiers feel healthier.
• 80% better energy efficiency than a neighbouring property that underwent a standard refurbishment, resulting in lower energy bills and reduced emissions.
• EnerPHit Passivhaus standard, which Grosvenor believes will increasingly be recognised by consumers as the platinum standard for healthy building, enhancing the buildings’ marketability.
• 95% operational CO₂ reductions, compared to pre-project, and 75% whole life CO₂ reductions, including embodied emissions of materials. This will result in 840 tonnes less CO₂ over the buildings’ 60-year lifespan.
• Convenience, with occupiers not needing to change their lifestyles to reap the efficiency and health benefits.

Find out more

Mike Levey

Retrofit Project Manager

Grosvenor Britain & Ireland

www.grosvenor.com