BowTieSprong is a revolutionary approach to wholesale retrofit of apartment buildings. It involves encapsulating the building with a new insulated airtight wall and a new warm roof with a maximally sized solar array. The new roof space forms a service loft providing access to the solar array, batteries, air source heat pumps and MVHR air handling units.

Energiesprong itself is a unique retrofit concept. It guarantees occupants a constant temperature in their living area of 21 degrees, '45 minutes' of hot water a day, a typical electrical plug load, all within a 'comfort plan' or service charge. Residents receive 24/7 filtered warm air delivered by mechanical heat recovery ventilation. These systems do not re-cycle air and are therefore safe to operate in a post-covid19 environment. Furthermore they prevent build-up of carbon dioxide and the depletion of oxygen indoors. The constant inflow of warm air without the need for active heating eliminates fuel poverty. This also eradicates damp and mould as all surfaces \\\> 19° and rooms are kept within the lowest Covid19 transmission humidity range of 40%-60%.

Hot water is heated by Air source heat-pump which eliminates the gas connection and standing charge eliminated. Boilers, wet radiators and associated plumbing are removed. Conversely, indoor temperature will never be above 26°, guaranteed by the Passivhaus design process.

This work occurs with residents remaining in-situ, a totally new possibility for a retrofit of this scale during which residents would normally be temporarily decanted at a high cost to the council and the additional risk of Covid19 transmission. This reduces stress on residents as they do not have to leave their homes and belongings or worry about the security of their homes while they are away. In addition there is very little internal access required to the properties, minimising the risk of Covid19 transmission between workers and residents

As a signatory to 2015's COP 21 Paris agreement, the UK is bound by law to reduce the carbon emissions of its buildings to Net Zero Carbon by 2050\. No government roadmap exists describing the steps to achieve this. EnergieSprong as a concept and BowTieSprong as a product solution shine a light on how to deliver this upgrade affordably and at scale.