Retrofit is a term used to describe any work done to upgrade an existing building's energy efficiency and reduce fuel bills. It will most often involve improving the existing building's construction (or 'building fabric') in order to reduce heat losses and may also include changing the way that energy is provided and used to heat and power the building.

Our approach to retrofit is to follow the passivhaus 'fabric first' principle of improving the existing building's ability to maintain thermal comfort for the occupants with minimal energy use. In the UK, this means reducing heat losses by:

• improving the levels of insulation

• upgrading to triple glazed windows/ doors

• improving the airtightness of the building fabric

Whilst working on a strategy with the client for these improvements, we model the existing building using specialist software and the anticipated impact that different proposals will have on their property. This helps determine the best course of action for fabric upgrades. If the modelling and discussions with the client indicate that it is appropriate, we will then also consider:

• upgrading the ventilation strategy for the property using either MVHR (mechanical ventilation with heat recovery) or a localised heat recovery ventilation strategy.

• switching to the use of heat pumps for the provision of hot water/ heating (air source or ground source heat pumps may be appropriate)

• where and how much solar hot water/ solar PV panels can be installed and how effective they will be given any shading that may be unavoidable due to the existing context.

Adding insulation into older properties can present technical challenges and the risks need to be considered and managed carefully.