Energy Retrofits In Older Homes: A Case Study

Older two story grey stone houses, Victorian or earlier
Many European towns and city face a significant uphill challenge when it comes to greening old, uninsulated housing.

Climate change is a compelling argument for doing things differently. In northern climates at least, our homes contribute significantly to greenhouse gas emissions and rising global temperatures. Researchers have assessed that if we lived in homes that achieved the Passivhaus EnerPHit rating1, energy use would go down and emissions would go down without sacrificing indoor air quality.

What could we do?

Going forward, all new dwellings could be built to the Passivhaus EnerPHit standard. This is not without its challenges. For example, building codes need to be revised and construction trades need to be trained. It can certainly be done, even building new housing for people with very low incomes2. And while it is a good idea, it won’t make much difference overall.

The new stock that gets added every year is a drop in the bucket. The thing we really need to come to grips with is the existing supply of housing, which contributes the lion’s share of the emissions. We’ve reported some very promising retrofits3.

Questions

What happens when the buildings to be renovated are over 100 years old? This is an important question in Glasgow, where there are 73,000 homes in traditional tenement structures (multiple homes under one roof4)? This housing style is quite different from the examples that have been reported above.

Should tenements be torn down and replaced? Should they be retrofitted? Is the Passivhaus EnerPHit standard the best retrofit choice? The issue is pressing, partly because housing associations5 in Scotland own homes in tenement buildings. As well, the Scottish government has decided the housing associations should reduce energy emissions ahead of all other owners.

Someone(s) decided to stage a real world experiment. A vacant eight unit tenement was purchased and renovated to the Passivhaus EnerPHit standard. A dedicated team of researchers has been tracking the physical work to document and evaluate the process. The renovation started in 2020 and took two years, partly because of the extensive documentation and partly because renovations usually uncover things that weren’t part of the plan but need to be fixed. COVID was also a factor. The first assessment has just been published.

Results

This assessment used a cost-benefit analysis6, which allows comparisons between three different scenarios:

  • demolition/rebuild,
  • retrofit to the Passivhaus EnerPHit standard and
  • retrofit to the Scottish government’s Energy Efficiency Standard for Social Housing 2 (EESSH2) standard.

On the question of demolition/rebuild vs retrofit, they concluded, “retorofitting is a better social investment than demolition and new building.”

The authors do not provide a definitive answer to the question of which retrofit standard gives the best result. The Passivhaus EnerPHit is more expensive to implement than EESSH2, but until people move in and live in the retrofitted units, the question remains open.

Why does this matter?

This project provides evidence on which to base decisions in Scotland. It also provides an model to facilitate decision making in other jurisdictions.

The full cost benefit analysis see is available for public review at the UK Collaborative Centre For Housing Evidence: A cost-benefit analysis of a traditional Glasgow tenement net zero retrofit

Footnotes

  1. Read more about EnerPHit at the Passive House Institute: EnerPHit Certification
  2. Try: Plucky Norwich Council Bridges The Energy-Affordability Divide
  3. Try: Is EnerPHit the Future of Affordable Housing? and Public Housing, “Reverence For Pre-Existing Structures” Captures Architecture’s Top Prize
  4. Tenement descriptions vary from place to place. According to Scottish law, a tenement is defined as being “two or more related but separate flats divided from each other horizontally”. Read more, view pictures at iWhy Hyndland in Glasgow is the only place in the UK protecting its tenements
  5. In the UK, housing associations are non-profit housing providers that offer affordable social housing (rent geared to income) as well as other kinds of supportive housing. Read more at the National Housing Federation: What housing associations do
  6. Cost-benefit analysis allows researchers to create financial values for social and environmental impacts. As well, it accounts for effects that take place over time. For more, check Wikipedia: Cost-benefit analysis