Trade offs can provide the solution

Gone are the days when an extension to a dwelling consisted of a ‘flat roofed’ box on the back of the house, writes Richard Smith, of Elmhurst Energy Services.

Householders are looking for far more contemporary designs in their buildings which often include larger areas of glazing or even fully glazed structures, but obtaining Building Regulations approval for extensions with a high degree of glazing has proven difficult for some architects and builders.

This is because Part L1B of the Building Regulations limits the amount of glazing to a total of 25% of the floor area plus any window/door openings that would be covered over by the extension.

There are other ways, however, to demonstrate compliance with the glazing requirements. One method requires an energy calculation involving the averaging out of all of the ‘area weighted ‘U’ values’ of the extension and comparing them to the average ‘U’ value of a notional extension of the same size where the minimum standards of L1B have been met including the glazed areas.

If the proposed ‘area weighted average U value’ is lower than that of the notional extension then the proposed extension is compliant.

An even more flexible method of achieving compliance is to calculate the CO2 emissions for the building as a whole, including the extension, using SAP 2005. This figure is then compared to a notional extension calculation and if the CO2 emission rate is lower in the proposed building compared to the notional extension, the proposed extension complies.

There is a major advantage to including the whole dwelling in this calculation. When improvements need to be made to reduce the CO2 emission rate it would be easy to assume that those additional improvements would be made to the extension itself, but if it is to be highly glazed other substantial improvements to the constructional fabric would be required to achieve the same standard as a notional building.

In many cases, the best method of enhancing the building to meet the Building Regs is to improve the existing dwelling as a whole. This could include additional loft insulation, a replacement condensing boiler or even cavity wall insulation.

By using the existing dwelling to enable the extension to meet the required standard, substantial energy improvements are being made - this is ideal in older dwellings, which probably have lower standards of insulation and older heating systems.

In the case of a more recently built property, there may be more difficulties in making the building comply and the architect/builder/conservatory contractor/heating or cooling engineer or indeed householder may have to consider the addition of renewable energy sources such as solar panels to change the compliance calculations.

Photos show apropos conservatory extensionswww.apropos-conservatories.com

More information: www.elmhurstenergy.co.uk