1950s New York Building

Two new publications – one from Europe and one from New York –  reveal case studies on deep energy retrofits.

The Royal Institute of British Architects recently hosted a book launch and panel discussion around the new book “EnerPHit: a Step by Step Guide to Low Energy Retrofit” by James Traynor, managing director of UK-based ECD Architects. 

EnerPHit is a “Quality-Approved Energy Retrofit with Passive House Components” certificate aimed at achieving energy savings of up to 90 per cent in existing buildings.

The book features several case studies of Passive House retrofits from the UK, Europe, and the US. 

ECD stands for “Energy Conscious Design”. The firm was a founding member of Passivhaus Trust in the UK in 2010, and since its first attempt at an energy retrofit to this high standard with a multifamily residence in situ, Wilmcote House it has used the EnerPHit standard because of its ability to interrogate the building performance and design to meet a very high standard. 

Traynor’s book builds on the work of other practitioners such as Sofie Pelsmakers and Nick Newman, both of whom have written books on the practice and economics of Passive House.

“Dealing with existing buildings is challenging, especially with building residents or occupants in situ,” Traynor says. “EnerPHit gives us the confidence that the retrofit is going to work.”

His book also explains the benefits of deep energy retrofits to other issues such as fuel poverty, the health of the occupants and social justice.


Although it might be more expensive to upgrade the entire building envelope compared to a lower standard upgrade, Traynor says, savings compensate for this. 

“In our case, we didn’t have to replace the services, which was a big cost saving for us. The residents were not going to need to heat their homes when it was completed. So we saved ourselves quite a lot of money by not having to spend money on the heating system.”

Upgrading the entire building envelope can mean that the existing heating system has to be reduced, however. He cites the case of a university in Innsbruck, Austria. “They actually had to take away a lot of the radiators because the risk of overheating was too high.”

Traynor’s book launch featured nine case studies, including from Latvia and Ireland, and the book makes the case that you don’t have to do the retrofit work all in one go. If the client does not have the finance to retrofit the entire building to the required standard, work can be staged (see below for more on this).

On financing deep energy retrofits, Traynor said he thinks that there is a message for institutional investors, who can plan 20 to 30 years ahead, and for long-term building owners who, if they’re going to benefit from the fuel savings and can demonstrate this to investors, don’t need outside funding.

It’s also about uplift in building value

But there’s a stronger message on making the financing case identified in a report from New York City on EnerPHit projects.

It argues that evaluating energy efficiency projects by the number of years it takes to pay back the expenditure from utility savings is not good enough for a deep retrofit that transforms a building. “Instead, we should evaluate these projects based on their impact on the total value of the building.”

In New York, the costs of the optimal retrofit are roughly 12 per cent of the current market value of a property. New apartment buildings have an average sale cost roughly twice that of a building needing a makeover. 

So a retrofit that features a completely new exterior skin, vastly improved interior conditions, and highly responsive, efficient systems will deliver an increase in market value several times greater than the costs.

A better business case should also find a way to value the more general benefits to society as a whole of these projects and apply them to the individual building.

The emphasis of Building Energy Exchange’s study, “Pursuing Passive: Strategies for a High Comfort, Low Energy Retrofit in NYC,” is on selecting energy conservation measures and phasing these measures over time, while the building is occupied. 

The report also describes how capital planning for such measures might be organised, code and regulatory barriers to pursuing this deep retrofit, and the most important technical and market challenges. 

The New York project

The deep energy retrofit study looks at a 1950-built 15-storey residential apartment block in Brooklyn that’s typical of many buildings in New York City, with masonry exterior walls and 163 apartments. 

It has many of the common challenges found by anyone wanting to apply a deep retrofit of an occupied multifamily building.

The project vision replaces all windows with high performance units, reclads the façade with insulation and an airtight layer, upgrades the ventilation to a balanced system with heat recovery, replaces the heating and cooling system with a high efficiency one and installs LED lighting energy efficient appliances.

The Passive House approach was first favoured by the NYC’s Greener, Greater Buildings Plan which required large buildings to benchmark their annual energy and water use, and to undergo a whole building energy audit once every ten years. 

This requirement has been improved with the 2015 policy OneNYC which has the goal of reducing citywide carbon emissions 80 per cent by 2050 on a 2005 baseline.


Although doing a complete retrofit all at once will give the highest benefit the soonest, the study explores the different benefits of phasing in order to minimise disruption to residents.

The following rather conservative phasing was proposed in this case:

Year 0 Envelope 1: windows + roof insulation

Year 4 Ventilation system (balanced ERV system + exhaust)

Year 8 Envelope 2: wall insulation & airtightness

Year 12 Replace heating/cooling systems with VRF system

Year 16 Replace domestic hot water boiler with high efficiency model

Anytime Upgrade lighting to LED, upgrade elevators, install energy efficient appliances

The report does find significant barriers remaining to a widespread application of deep energy retrofits. 

More analysis of the benefits to different building typologies is needed  to determine the best guidance for owners. It calls for modular retrofit systems for each typology to be developed, and a better grasp of the financial and policy instruments to incentivise the market.

It also wants to see steps taken to bring some of the equipment costs down and much more training for architects, engineers, consultants, building owners, managers and the finance sector who all influence decisions about buildings and the way they can be improved so they use less energy.

David Thorpe is the author of Passive Solar Architecture Pocket Reference,  Energy Management in Buildings and  Sustainable Home Refurbishment. Learn more by enrolling on next year’s online Post-Graduate Certificate in ‘One Planet’ Governance.

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