JV3 method is a pathway to energy compliance with way more flexibility compared to the rigid Section J DTS pathway. JV3 assessment is a comprehensive modelling approach that covers the building fabric (roof/ceiling, walls and floors), external glazing and services (space heating and cooling equipment, solar PV …) in a single model (i.e. proposed model). This model is then compared to a same model having building fabric and services as required by Section J DTS provisions. If the proposed model emits less carbon emissions than the reference model, then the proposed building achieves energy compliance. This method allows installing single glazed windows instead of complying double-glazed, add no insulation to the walls or keep a low-performing gas boiler, by offsetting the energy loss via better insulation elsewhere or installing solar PV, etc. (which is not possible under DTS pathway)