Standard Assessment Procedure ~ the Approved Document to Part
L of the Building Regulations emphasises the importance of
quantifying the energy costs of running homes. For this purpose it
uses the Government's Standard Assessment Procedure (SAP). SAP
has a numerical scale of 1 to 100, although it can exceed 100 if a
dwelling is a net energy exporter. It takes into account the
effectiveness of a building's fabric relative to insulation and
standard of construction. It also appraises the energy efficiency of
fuel consuming installations such as ventilation, hot water, heating
and lighting. Incidentals like solar gain also feature in the
calculations.
As part of the Building Regulations approval procedure, energy
rating (SAP) calculations are submitted to the local building
control authority. SAP ratings are also required to provide
prospective home purchasers or tenants with an indication of the
expected fuel costs for hot water and heating. This information is
documented and included with the property conveyance. The SAP
calculation involves combining data from tables, work sheets and
formulae. Guidance is found in Approved Document L, or by
application of certified SAP computer software programmes.
SAP rating average for all homes is about 50. A modernised 1930s
house about 70, that built to 1995 energy standards about 80 and
a 2002 house about 90. Current quality construction standards
should rate dwellings close to 100.
Ref. Standard Assessment Procedure for Energy Rating of
Dwellings. The Stationery Office.
Air Permeability ~ air tightness in the construction of dwellings is
an important quality control objective. Compliance is achieved by
attention to detail at construction interfaces, e.g. by silicone
sealing built-in joists to blockwork inner leafs and door and window
frames to masonry surrounds; draft proofing sashes, doors and loft
hatches. Guidance for compliance is provided in, Limiting thermal
bridging and air leakage: Robust construction details for dwellings
and similar buildings, published by The Stationery Office. Dwellings
failing to comply with these measures are penalised in SAP
calculations. Alternatively, a certificate must be obtained to show
pre-completion testing satisfying air permeability of less than
10 m^3 /h per m^2 envelope area at 50 Pascals (Pa or N/m^2 ) pressure.
Thermal Insulation Energy Efficiency of New Dwellings