Saturday, 10 September 2011

Sap Calculations Explained

Standard Assessment Procedure (SAP)

SAP - or Standard Assessment Procedure
SAP is the current method used to obtain energy rating for new build homes or dwellings also known as
"on construction" dwellings. The procedure is used to determine heat losses and thermal characteristics
of the property by examining the building's plans, the construction materials used in the build and
additional factors including space and water heating
SAP is based on a notional dwelling built to the 2002 standards with a target reduction of 20%.

SAP Assessment & SAP Ratings
(1) SAP Assessment - this is a calculation of the CO2 emission rating which is submitted to Building
Control for new build which must meet the latest Building Regulations for energy efficiency.
(2) SAP Ratings - this is a cost based rating system and provides guidance to home buyers on a home's
annual energy costs and usage from heating, hot water, and ventilation.

Target Emission Rating (TER)
Firstly, a new dwelling has a Target Emission Rating (TER)
The TER is based on the dwellings size, shape, and form of build detachment. The target calculation makes standard assumptions about other design specifics for the property, for example the type of heating used,
standard of insulation in the construction, and the amount of glazing in the property.

Dwelling Emission Rating (DER)
Secondly, a new build dwelling emission rating (DER) is calculated, this is based on all the actual design
specifics. In order to pass the Building Regulations, the DER must be no greater than the TER. Using this
method ensures that it is no more onerous for large detached dwellings to achieve compliance than small
terraced homes.

SAP Ratings
A SAP rating provides a rating based on energy costs for example higher rated dwellings have lower
energy losses and as a result will be cheaper to run. The costs associated with cooking appliances and
domestic appliances are excluded from the rating. The scale applied to ratings is from 0 to 100
A property with a rating of 100 will have a zero net cost for space heating, hot water, and ventilation.
Dwellings using a costly form of energy, such as electricity, will be rated lower due to the higher costs of
the "fuel" used.
SAP ratings make standard assumptions about a home's occupancy, the internal temperatures in
rooms, heating appliance usage, and geographical location of the dwelling. Ratings are based upon
costs per square metre of living space in the dwelling, and are essentially independent of dwelling size
for a given built form.

SAP ratings also have a banding system, from A to G, like those used to rate domestic appliances, the
banding system.
Band A properties are rated at 92 and above, Band B is in the range 81 to 91, and Band C in the range
69 to 80. Most new dwellings built to 2006 Regulations have ratings of around 80.
Use of an expensive form of energy for heating, such as "on peak" electricity, will result in ratings below
70, the method of heating and it's control plays an important part in determining the SAP Rating.

Report By :John Stobbs

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