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ICF Tech - advanced construction technology

Call us on 01773 850920


Meeting SAP 2009

The Standard Assessment Procedure (SAP) is the UK Government's recommended method for measuring the energy rating of residential dwellings. It calculates the typical annual energy costs for space and water heating, lighting and the CO2 emissions from a dwelling.

Currently, SAP 2005 is used as the basis for checking new dwellings for compliance with building regulations in the United Kingdom requiring the conservation of fuel and power since 6 April 2006 (England & Wales: L1 Approved Document), 1 November 2006 (Northern Ireland Technical Booklet F1) and 1 May 2007 (Scotland Technical Handbook 6, Domestic).

There are two fundamental areas of change between SAP 2005 and 2009; changes focused on improving the accuracy of the SAP methodology and those changes designed to make SAP more flexible, enabling a variety of new and existing technologies to be combined within a given dwelling.

The key areas of change in SAP 2009 are:

Party walls

In SAP 2005, heat loss through party walls is assumed to be zero. In SAP 2009, the U-value of a cavity party wall will be set to between 0.0 and 0.5W/m2K, depending upon the specification.

Developers must now design and build so as to eliminate air movement - for example, fully filling the party cavity in conjunction with edge sealing and possibly adding a 'cavity sock'. The U-values assumed by SAP 2009 are therefore taken as 0.50 for an unfilled, unsealed cavity, 0.20 for a sealed, unfilled cavity and 0.0 for a fully filled and sealed cavity.

Because our system is monolithic by nature and insulated on both sides of the cavity we meet the highest requirement of a 0.0 U value.

Thermal bridges

The only Y-value option available in SAP 2009 is the 'worst-case' value of 0.15. To better this, developers and SAP assessors will need to examine the detailing at junctions, such as between walls, floors, roofs, windows and internal walls and to properly assess the heat loss through thermal bridges.

Changes in the SAP methodology for carrying out these calculations also mean that the calculated thermal bridging heat loss may be significantly higher in SAP 2009 than for the same calculation in SAP 2005. This is because SAP 2005 ignored junctions with party walls and, where accredited construction details are not being used, the calculated values are multiplied by 1.25.

At ICF Tech, we have modelled all the important junctions to determine a psi value for each one.  This allows you to use a Design Y value (psi x linear length of junction) to determine the true Y value for the development. In reality this means that you will achieve a Y value of 0.013 for detached houses, exceptional!

Cooling and air-conditioning

SAP 2005 includes a risk assessment of a dwelling overheating in summer and is one of the criteria for Building Regulations approval. If dwellings overheat there is a risk that the use of portable and fixed air-conditioning systems will increase, with a consequent rise in carbon emissions.

SAP 2009 adds the ability to assess the need for cooling and the associated energy and carbon emissions from fixed air-conditioning systems.

Homes fitted with air-conditioning will therefore see an increased DER. As these systems run on electricity, the associated CO2 emissions can be substantial. SAP 2009 assesses the impact of air-conditioning from the A to G rating of the system and the external temperature for the region of the country.

Our system has a benefit that helps to eliminate over-heating, normally associated with timber frame; it’s called ‘decrement delay’ and is the time (in hours) that a structure stops the passage of heat from the outside to the inside.  Figures of between 8 and 12 hours is considered optimum, our system achieve 9 hours; timber frame achieves as little as 3 and explains why they always overheat.

Thermal mass

Thermal mass is a measure of how 'lightweight' or 'heavyweight' a building is. Timber frame is typically a lightweight construction, whereas a building with external, party and internal walls made from heavyweight block and with concrete lower and upper floors is typically heavyweight. Heavyweight energy-efficient homes generally make better use of solar gains in the day by absorbing them and radiating the warmth later on as the level of solar radiation drops.

Due to the dense concrete, our system is deemed ‘heavyweight’ and due to the way our system integrates the thermal mass of the walls with that of the ground and intermediate floors (if concrete floors are used) you are able to maximise the thermal mass effect as the ICF walls will act as a heat sink, taking heat away from the floor.  Due to the insulation on both sides of the ICF the Thermal Mass Parameter (TMP) is not optimal due to the way TMP is measured (to benefit masonry walls) but because our walls us dense concrete we still get the same TMP as masonry, but much better decrement delay, thermal performance, air infiltration, acoustic performance......