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Retrofit is the upgarding of an existing building to reduce carbon emissions, reduce fuel bills and improve comfort, health and wellbeing. Many of our existing homes are too cold in winter and too hot in summer, and suffer from poor indoor air quality. Retrofit can involve repair, renovation, refurbishment or restoration of an existing building.

Why retrofit?

There is currently a climate emergency, caused by greenhouse gases being released into the atmosphere. We emit huge amounts of CO2 by simply heating our homes and heating hot water. The UK's existing housing stock is responsible for 18% of all of our annual national emissions. Retrofitting our existing buildings is critical if we are to achieve net-zero by 2050.


UK is currently facing the challenge of retrofitting over 28 million buildings by 2050. 80% of the UK homes that will exist in 2050 have already been built and because our current building standards are not achieving net-zero, even the houses we are building now will need to be retrofitted before 2050. 

Retrofit Strategy

Retrofitting an existing building does have some risks. A poor retrofit can damage the fabric of the building and cause overheating, poor indoor air quality, damp or mould growth. Different buildings will require a different approach to retrofit and there may be constraints on what can be done. Many homes are semi detached, or mid terrace. Some properties may be Listed or the visual appearance may need to be retained.


If you would like to retrofit an existing building JMP architects can help by preparing a Retrofit Plan. We can look at a whole house approach to the work and the sequencing of the work. A retrofit may be carried out in one go, or use a step by step approach, which may be carried out over a number of years. 


There are a number of elements to the building we can look at but the fabric is the single biggest factor in determining the performance of a building. Think Fabric First.

Insulation - will reduce heat loss and energy consumption. 

New windows and doors – will reduce heat loss and energy consumption. 

Air tightness - Draught proofing reduces uncontrolled ventilation and heat loss. 

Ventilation – controlled ventilation is essential to avoid overheating, poor air quality, or condensation. A mechanical ventilation system with heat recovery (MVHR) will be required.

Thermal bridges – improved insulation and air tightness will highlight thermal bridges in the building's fabric as cold spots where condensation and mould can form. 


Once the best possible standards of insulation and air-tightness have been achieved, the proposed refurbishment should be thermally modelled to determine what will probably be a much reduced space heating demand. A new heating system should be then considered.

Heat pumps – are powered by electricity. If the fabric of the building is not improved first to reduce heat demand, the building will not be thermally comfortable and electricity bills will increase. There will also be an increased demand on our National Grid System. 

Heat emitters – if changing from a gas or oil fired boiler to a heat pump, you will find that heat pumps produce heat at a lower temperature than traditional boilers.  Underfloor heating works best with heat pumps, or large low temperature radiators.

Hot  water - You may consider solar water heating to provide hot water in the summer. Solar water heating is efficient, cost effective and has no emissions.

After space and water heating, electrical power is the next largest burden on a building’s energy consumption. Electricity is used to power appliances, fans, pumps, for lighting and for cooking. Currently, most electricity is generated using fossil fuels and distributed through the National Grid. On site renewable electricity generators should be considered to reduce the demand on the National Grid.

Photovoltaic panels - are tried and tested domestic renewable energy generators. PV panels will produce electricity during daylight hours, the stronger the sunlight the more electricity is generated. Electricity can be fed back to the National Grid or stored in batteries, inside the building, to be used later.

The EnerPHit standard

The Passivhaus standard can also be applied to retrofit projects to achieve similar savings in space heating requirements. The EnerPHit standard is for the refurbishment of existing buildings which cannot achieve Passivhaus Standard due to the existing building form, existing orientation or existing context. The EnerPHit standard can be achieved in one of two ways; either based on the requirement for heating demand or on the requirements for individual building components. Both methods rely on Passive House principles to improve energy efficiency.

The Passive House Planning Package (PHPP) is used to model the building to verify that the EnerPHit Standard will be met. A Passivhaus Certifier is required at an early stage in the process. Design and technical information and the PHPP are submitted to the Passivhaus Certifier to assess the detailed design. Supporting information, such as air test results, ventilation commissioning, construction photographs, are also required for EnerPHit Certification.

Why EnerPHit?


EnerPHit Certification is a voluntary standard. The current Building Regulations in the UK include relatively low refurbishment performance targets. If we are to achieve net-zero by 2050 we need to improve our existing buildings to a much higher standard than just Building Regulations compliant.

Studies have shown that building to the Passivhaus or EnerPHit Standard will result in a better quality construction. A significant number of Passivhaus buildings have been monitored and have demonstrated that they perform, in terms of energy consumption, as predicted. The gap between predicted and actual performance is reduced.

The certification of a Passivhaus or EnerPHit building using an accredited Passivhaus Certifier will provide assurance to clients that new buildings are built to a higher standard.

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