Jonathan Braddick - RIBA Chartered Architect Devon
01395 265768

BRE has just released its proposals on how the SAP methodology should be changed in line with the planned revision of Building Regulations in 2013; the next step towards proposed Zero Carbon houses by 2016.

It should be noted that this is consultation stage only.

There are eight key changes which may be relevant on upcoming housing developments.

This consultation only applies to the calculations used for producing SAP assessments and EPC's. It does not cover Target Emission Rates, limiting U-Values or minimum heating / lighting efficiencies, these will be released later this year as part of the Part L 2013 consultation.

1. More Specific Locations:

Emission rates have not been tied into site specific geographical location before now; you could build two identical houses - one on Bodmin Moor and one on the Orkneys - and you're EPC results would be identical. That's set to change, as the location of your site will be defined in one of 21 regions in the UK - each region will use different figures which measure four key areas:

a.      External temperature: Monthly figures will be used in the new SAP which will have a direct effect on the amount of heating and cooling your dwelling needs. This figure will also take into account your height above sea level.

b.      Wind speed: Again, monthly figures will be used based on your location. This will have a direct effect on the dwelling's ventilation rates, and will also give more accurate results for houses with wind turbines.

c.       Solar radiation: The amount of available sunlight will again by measured monthly and regionally and will affect the solar gains calculations (how much natural light and heat comes in through the windows) and will also change the efficiencies of solar panels.

d.      Latitude: Your location on the Earth's curve will also change the effectiveness of solar panels and the amount of daylight hours you experience.
In the past, all of these figures have been based on UK averages. This change is likely to mean warmer, brighter parts of the UK will benefit with lower emission rates, but how much of a difference remains to be seen.

2. Seasonal Heating Length:

Under current SAP calculation, heating is expected to be used from October 1st until May 30th and, if relevant, cooling systems from June 1st to August 31st. This is irrespective of regional temperatures and daylight hours. This is set to change as SAP moves into regional data. Houses which use less heating will have lower emission rates, but houses with higher cooling needs will have worse emission rates.

3. Emission factors:

Every fuel source (electricity, gas, oil) has an emission factor; that is the amount of carbon emissions produced per kilowatt of energy used. The carbon calculation takes into account the production of the fuel, and getting it to your house. All factors are planned to be adjusted for SAP2013, and practically all fuel sources will have higher factors than currently. The emission factors of gas and oil will be increased by around 7%, logs and biomass are also increasing. Electricity will retain the title of Highest Emission Factor, but will only be raised by 1%.

4. Increased Accuracy for Solar:

There are two possible changes to the efficiency of solar thermal panels. This will make the new SAP data more accurate for those houses which are fitted with them. The specific angle of the panels will be recorded (currently SAP can only deal with panels at plane, 30, 45 or 60 degrees), and additional efficiency data will be required from the manufacturer, known as the ‘second order heat loss coefficient'.

5. MVHR Installation:

If a mechanical ventilation system is to be installed, unless it can be proven that it was installed by a competent person SAP may penalise you. This is being proposed following field studies which have shown just how inefficient these systems can be if not fitted correctly.

6. Thermal Bridging:

Accredited Construction Details continue to grow in importance as builders are encouraged to do their best in eradicating cold spots from new houses. The new SAP is likely to go into more details than before and include more junctions than before.

7. Heating Controls:

An approved list is likely to be produced which shows the various makes of weather compensator and zone control systems which are available in the marketplace.

8. Circuit Loss:

The amount of heat lost through pipe-work may become more detailed than before. Currently SAP just needs to know if primary pipe-work is insulated or not. This is likely to be changed and will be based on the amount of insulated pipe-work and the type of heating controls used.

The full methodology is downloadable from the BRE website and comments are being accepted until the end of March. The aim is for the changes to go live next year.