RdSAP (Reduced data Standard Assessment Procedure) is the UK government's methodology for assessing the energy efficiency of existing residential properties for Energy Performance Certificates. It uses simplified inputs gathered during a site survey rather than the full SAP calculation used for new builds.
Also known as: Reduced data SAP, Reduced data Standard Assessment Procedure
RdSAP was introduced in 2005 to make EPC assessment of existing homes practical at scale. Full SAP (Standard Assessment Procedure) requires detailed construction drawings, U-values for every fabric element, and full HVAC specifications — fine for new builds where the architect has all of this, impossible for assessing an existing 100-year-old terrace.
Instead, RdSAP infers building fabric properties from observable features: age-band of the property, type and number of external walls, glazing percentage, loft insulation depth, heating system, hot water system, secondary heating. The Domestic Energy Assessor (DEA) gathers this data during a 30–60 minute site visit using a Government-accredited RdSAP software (e.g. NES RdSAP, Stroma RdSAP).
Floor plans with GIA per room are a required RdSAP input. The plan does not need to be construction-grade — but it must be measured accurately to ensure heat-loss surface areas are correct. EPC floor plans from VizCraft are formatted to the data structure RdSAP software expects.
VizCraft delivers this work for UK estate agents, photographers and developers — typically within 6–12 hours.