Glossary

This is defined by the Centre for Sustainable Energy as “...any improvement work on an existing building to improve its energy efficiency, making them easier to heat, able to retain that heat for longer, and replacing fossil fuels with renewable energy.” We are facing in the UK two major challenges. The first is rising energy bills making it harder and harder for people to keep their homes warm. The second is that we need to urgently reduce our carbon emissions if we are to reach “net-zero” by 2050.

But there is also a third challenge which is happening right now - greater climate instability and extreme weather events. We are now more exposed to heatwaves, extreme cold, storms, flooding and wildfires than we’ve ever been - and the buildings that we have aren’t designed for it. In some cases modern design makes the risks worse i.e. petroleum based products allowing easier spread of fire, our love of big glass walls and conservatories rendering spaces to hot in summer and cold in winter. We can’t stay in the realm of “mitigating” climate impact anymore as a lot of that impact has already happened, and we’re seeing the results. So retrofit needs to broaden its definition beyond mere efficiency to consider “adaptation” - buildings that will persist, resist and remain serviceable anything up to seven generations into the future whilst our climate is breaking down.

But adaptation can mean more than just dealing with a changing climate. We may also need to adapt buildings to work for people. There is an endemic problem of ableism in our built environment, excluding or overlooking people with disabilities. And by extension, ageism. Very frequently I’m finding that to “futureproof” homes, especially for clients in later life, accessibility and climate adaptation go hand-in-hand. Not to mention that wide doors and level thresholds are also needed for very able bodied parents pushing their young’uns around in pushchairs!

These are buildings that use incredibly low amounts of energy to heat. They give you a very stable internal climate and high internal air quality. They need much higher levels of insulation and airtightness than an ordinary new-build home, and they require a controlled ventilation system that can also recover the heat generated in the home.

Windows tend to be triple glazed, and junctions/connections need to be wrapped as best as possible in a blanket of continuous insulation. Their form needs to be compact to conserve heat i.e. reduce surface area in relation to floor area. When designing a Passivhaus you are relying less upon the central heating system of the home and more upon capturing “free” heat. This can include heat generated within by everyday living (i.e. cooking, showering, occupants themselves) but even more importantly, the heat from the sun which streams in through the windows. Therefore the orientation of the building and sizing of the windows need to be optimised to make best use of the sun’s gift of free energy, but at the same time not making them too big in the wrong places as the home can then overheat.

Our recent summer has proven how careful we need to be with glazing sizing and correct use of solar shading. In order to keep the design on track to become a Passivhaus I use a software called PHPP which is based on sound building physics. It’s much easier to design a new-build as a Passivhaus but it has also been achieved on retrofits too!

Sometimes Passivhaus doesn’t seem like its a viable or practical target. Other standards exist that suit different situations i.e. EnerPHit, PHI low energy standard, AECB Carbonlite, LETI etc. I can help you navigate the range of options that are available.

When we look at existing buildings we need to understand how they work. Modern buildings built with modern materials don’t function like traditional ones. Older buildings are more happy to get wet and concentrate on being able to dry out, whilst modern buildings don’t really want to get wet in the first place. Modern retrofit solutions applied to traditional buildings can be risky if not carried out properly i.e. a closed-cell and sealed-up internal wall insulation product to a solid brick Victorian wall is inadvisable as it can promote condensation in the wall where it can’t escape. It makes the wall perform worse thermally as it’s now constantly wet. Worse still it can promote mould growth and eventually structural damage.

These are points at which heat can conduct out of the junctions and edges in the structure i.e. where the wall meets the floor or roof, balcony fixing points, pipes and service penetrations etc. Looking in detail at the cross-sections of these junctions is important so we can ensure as much continuity of the insulation around these junctions as possible.

An airtightness layer needs to be installed on the inside of the insulation. Without airtightness, the nice temperate air inside the home will readily escape out, and with it all that valuable heat (or coolth if the weather outside is warm). Of course we need the building to be ventilated (more than ever if we are wrapping it in insulation) but we want to transition the building into doing this in a controlled rather than uncontrolled way. Beyond a certain level of airtightness this becomes absolutely neccessary (we look to systems called MEV or MVHR). I believe that when it comes to retrofit, we should install at least a whole house mechanical extract system in most cases. It’s important to have a continuous air barrier - gaps in this, in an especially fine-tuned building like a Passivhaus or deep retrofit, lead not only to the warm air escaping the structure, but the moisture it carries with it. This can then condense in the structure. It may create convection loops inside the fabric that devalues the effectiveness of the insulation and lead to mould and structural damage via condensation.

Very often the airtightness layer is serving the purpose of vapour control i.e. reducing the vapour in the air that diffuses from the warm internal environment through the wall/floor/roof to the outside (where it can condense into water somewhere in the structure on its way) and also help, to an extent, drying of any condensation back to the inside (especially in summer months where this is likely to happen most). Well, this is what an “intelligent” vapour control layer should do. “Unintelligent” ones such as polythene should be used with great caution. Sometimes, though, the airtightness layer is not doing so much vapour control i.e. an internal plaster face on a solid brick wall is airtight but not vapour tight. How does this happen? Well, apparently molecules of water vapour are smaller than air!

This is the means by which our buildings can conserve heat or coolth. Insulation materials are those that encourage a still air or gas barrier in or around them which means that they are resistant to the conducting of heat between the inside and the outside of the building. Some insulation products are more insulating than others but this isn’t the whole story. Different insulation products are used to achieve different things. Some are more vapour open, cheaper, lower in carbon, higher in chemical nasties, waterproof, fire resistant, longer life, better at storing heat in their mass, fluffy/rigid, the list goes on!

PAS 2035:2023 is a standard method developed by the British Standards Insitute and has now been made mandatory for any public sector retrofits. It is a step-by-step, almost scientific approach to design and risk management to make sure that a retrofit is done safely. It requires three professionals working in tandem - a retrofit assessor (who would also be a domestic energy assessor), a retrofit designer and a retrofit coordinator. The assessor is like the surveyor, the designer like an architect and the coordinator like a risk and compliance manager. I am fully qualified to be a retrofit coordinator whilst all my architecture and retrofit experience allows me to perform also the role of retrofit designer if on a private scheme. Nevertheless, retrofit needs to be a collaborative effort, and for such work I seek partnership with qualified retrofit assessors such as The Green Heat Coop and Cambridge Retrofit Hub.