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enbee architecture + design, Muswell Hill Low-Carbon House, whole house retrofit (before), London, N10
enbee architecture + design, Muswell Hill Low-Carbon House, whole house retrofit, London, N10

What is retrofitting homes? What is retrofitting with natural building materials?


Are you thinking about your energy bills this year? With our current energy crisis, I assume most people in the UK are. This has been an extraordinary time, Brexit, Covid, Ukraine and the energy crisis.


How has your home performed this winter?


I have been asking this question of friends and of people I meet. With the crisis, how warm are you now keeping your house in the winter, over 20 degrees? Over 18? To my surprise, many reported much lower temperatures, below 16 degrees, some as low as 12 degrees.


Some of the questions I have asked clients and friends are: is your home cosy and warm, with consistent temperature throughout? Is it draft-free and is it affordable to heat? Usually, the answer is no. The houses are reported as drafty, damp in some areas, sometimes with mould in and certain areas particularly hard to keep warm. Some areas were so cold they were reported as too uncomfortable to sit in during the winter months and not surprisingly some reported their health was affected as a result.


Sadly our old housing stock was never really designed with energy efficiency in mind. In the UK, we have a temperate climate and energy has been relatively cheap. It didn't matter too much that our houses leaked like sieves. Go to countries further north and necessity has forced far better building practices, Sweden, Switzerland, Germany... Canada. You can't get away with leaky properties in long periods of subzero temperatures. Performance in such countries is key.


What can we do to address the climate emergency when renovating? Can we both improve our home environment and make a difference?


As we progress through the 2020s with increasing urgency to keep warm as well as to reach UK Zero Carbon targets, what part does the performance of our building play? Back in 2015, after watching my first Panorama-type programme on our changing climate, I was struck by its potential speed. One scene that has stayed with me was scientists boring into the polar ice sheets in the Antarctic. By examining the layers that they could date back to other periods of climate change, they found that the world could warm very quickly once certain markers were met: 30 years as I recall. 30 years I thought to myself at the time, my eldest son would be in his early 40's in 30 years. 30 years, could even be in my lifetime. When I come across a problem, my natural inclination is to fix things but what can one person do? What can I do? Something needs to be done, I told myself.

enbee architecture + design, Muswell Hill Low-Carbon House, brick clad timber frame + woodfibre wall, London, N10

Image from Muswell Hill Low Carbon House shows a timber framed wall insulated with woodfibre and faced with salvaged bricks

What is retrofitting?


A couple of weeks later, I visited Ecobuild (now named Futurebuild). 'What can I do' was on my mind. I came across a stall for the Retrofit Academy running a course on retrofitting. They told me about reducing the energy consumption of homes through retrofitting properties, they told me that many of those attempting this without learning specifically how and having training were getting unintended consequences. They told me their course was based on 100 case studies, and they had worked out certain best practices. I was sold, I didn't have the funds for the course, but I had the will. I had to do this, this was something I could do to help people, to help change things, so I found a way, and I didn't want to wait for the London-based course so enlisted to start mid-way through a course in Milton Keynes and would finish the lectures in London. It was 10 days altogether over a number of months and was enlightening. I was super excited, often one of the keenest course members in the room. If you had met me as a student in my 20s and told me that I would be getting excited about insulation some 20 years or so later I would never have believed you. Back then design was my thing, I would have told you, I loved inspiring, beautiful architecture. I didn't really think too much about how it went together so long as the end result was strong and looked good, but I do now. Now performance is as important as design.

enbee architecture + design, Muswell Hill Low-Carbon House, solid brick wall insulated with woodfibre, London, N10

Image from Muswell Hill Low Carbon House showing application of woodfibre insulation

What are retrofitting unintended consequences? Can retrofitting cause mould? And what is a cold bridge?


Unintended consequences are problems that can occur with uninformed retrofit practices. The early retrofitters from Innovate UK's Retrofit for the Future projects started in 2010 had £150K allocated for 100 projects and through trial and error, discovered what did work, what didn't work and what could cause unintended consequences.


Insulation needed to be installed with no gaps around the entire building. Gaps caused the consequence of a cold bridge. Cold bridges were an uninsulated path for warm moist air that might condense on these cold areas and cause damage which can be in the form of mould and rot. Imagine a hot day and a glass taken from the freezer to hold some beer. The glass immediately steams up and frosts over. Moisture vapour condenses as it cools and settles on cold objects. Now imagine a steel beam, one end sitting on a cold brick wall, the other end inside a warm property that has been internally insulated. That steel beam has one end in the cold and the other in the warm. On top of this, it is a highly conductive material; the cold of the beam will pass through the insulation zone and warm moist air will find a cold surface to condense on. A cold bridge is exactly what it says on the tin, it is a route for the cold to get from the cold side to the warm side and vice versa.


Airtightness was discovered as also key to reducing energy consumption. Once a building has been insulated, if air leakage is not addressed, it can account for as much as 40% of the heat loss. We create a lot of moisture, through cooking, bathing, drying clothes and breathing. When I heard this I pictured sitting in a stationary car when it is raining. The air vents are off and within minutes it seems, the windows steam up and the moisture vapour has nowhere to go. Take a home, add a non-vapour open insulation internally that stops vapour from passing through it, and include sealing up all the drafts, the moisture we create has nowhere to go. Houses that had performed well were found to be full of mould. Insulation and airtightness; the key to keeping the heat in, had, it was discovered, to work hand in hand with good ventilation systems such as Demand Controlled Ventilation or Mechanical Ventilation and Heat Recovery (MVHR).


Vapour-closed insulating products such as PIR or foam-based or polystyrene-type insulation stopped old buildings from working as they used to. It changed the building's physics and could cause interstitial condensation. When you have a wall that is internally insulated there is naturally a join between the insulation product and the wall, during cold weather water could condense here making the join wet. The vapour-closed materials such as PIR are often also water resistant, so the water gets stuck in this location and water as we all know damages the buildings. It might cause hidden mould growth with the spores affecting occupants' health, or the bricks which usually get wet in the winter and dry in the summer, might struggle to dry out. Add repointing with the cement-based mortar in the mix and you have a recipe for potential brick spalling; if overly wet bricks freeze in the winter, the frost can cause the bricks to break up, elements can sheer off or they crumble.

The Construction Material Pyramid. Image © Centre for Industrialised Architecture (CINARK) from Royal Danish Academy
enbee architecture + design logo
enbee architecture + design logo

What are the best materials for insulation?


Is the word best relative here? Or are there actual 'best' materials? For example best could be based on cost/m2, i.e. affordability and commercial viability. 'Best' could be in relation to ease of installation, and recognised products that are known to the industry, again, this is helpful for commercial viability. Is 'best' to do with occupant health? Or how it links to the original performance of the building? Our ability to engage with the circular economy at the end of the lifespan of the product. Should 'best' be linked to our impact on the planet? Could 'best' even be linked to the products sequestering CO2?*.


The early retrofitters researched what worked best in their 100 case studies. Some placed moisture monitors at the join and experimented with different types of insulation and found that with period properties, the most favourable outcomes were natural materials such as woodfibre and cork. I rejoiced when I found this out, these materials were linked to nature, and health which are strong in my sense of values and I could work within them.


*What is sequestering CO2?


Products that sequester CO2 absorb it at some point in their lifetime. Something we need to do to reverse Climate Change and get our CO2 levels back in balance. Take a grown material, wood, straw, hemp, mycelium, or cork, these products absorb CO2 and they grow and release it back into the atmosphere if they are burned or rot and decay. By using them as building materials we lock that absorbed carbon into our buildings for the lifetime of the building, we remove it from the cycle of growth and decay; removing that CO2 for a good period of time.


What insulations are best for health?


Natural bio-based insulations deal with moisture far more effectively which greatly reduces the potential for mould growth. They are natural, so aren't filled with chemicals that our bodies were not made to absorb such as Volatile Organic Compounds (VOCs). Include sheep's wool or clay plasters, which absorb VOCs, to the mix of materials and good ventilation and air quality tests should come up far superior to those in a regular home.

enbee architecture + design, Ferndene Retrofit using woodfibre, London, SE24

What are good quality retrofit standards? 


Retrofit is complex and not to be undertaken lightly, however from these relatively quick-to-pick-up discoveries and a good deal of sophisticated predictive software, some experts qualified in building physics lending their expertise, a lot of training of professionals by the Retrofit Academy and the AECB, the industry has put together a set of best practices. Trust Mark, a government-endorsed body, has got involved and commercial retrofits work to certain codes such as PAS2035. We have Enerphit Certification (similar to Passivhaus but for retrofits). There are also the AECB Carbonlite Retrofit Standards.


We can work to any of these standards if required.


And as for our overall approach?


We believe that a low-carbon future will transform our world.

So we design our projects to reduce environmental impact.

We beautifully refurbish, retrofit and extend buildings with low-carbon, natural materials to meet high standards of energy efficiency and air quality.

If these things are important to you, come and chat with us.


This column is here to give you the benefit of some of the things we have learned over the years. If you have a project you would like to discuss in more detail, see our starter packages and contact form. 

enbee architecture + design, Muswell Hill Low-Carbon House, passive house windows, London, N10
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