Solutions to Document L

Guidance on Document L

The latest revisions to Building Regulations Approved Document L1A introduce new rules for the calculation of carbon emissions from houses. The changes not only continue to allow the use of open and glass fronted heating appliances within homes but also mean that their incorporation will offer a number of specific benefits in terms of meeting carbon requirements and homeowner appeal.

For the first time secondary heating appliances have to be specified as an integral part of completing the Standard Assessment Procedure (SAP) calculation. The performance of these appliances, the specification of associated chimneys and flues and building elements such as thermal insulation and glazing must all be considered together to arrive at a carbon emissions calculation.

By adopting this approach, the Government is targeting a 20% reduction in carbon emissions from new homes, as part of its commitment to meeting international environmental objectives.

The Changes In Summary

The new rules set out more stringent requirements for the energy efficiency levels achieved by houses. They offer the designer considerable flexibility. However, any elements which are likely to increase the use of energy must be balanced by greater thermal efficiency elsewhere. For example, if the window area is larger than normally expected, then higher levels of insulation may be required to offset this. The methodology is relatively complex but will
be made easier through the availability of special SAP calculation software.

To take advantage of these options it is necessary to install a natural draught chimney. This will offer a number of significant performance and financial benefits.

Benefits of Installing a Chimney

A key element within the calculation methodology is the adoption of electric heating as the 'default' secondary heating source. Electric is a carbon intensive energy source. This means that secondary heating appliances with carbon efficiencies better than an electric fire will offer a carbon credit which can be traded off in other areas of design.

The graph below shows the carbon savings of different fuel types relative to electricity.

■ Where a chimney/flue is installed and used in conjunction with a modern, efficient gas, wood or multi-fuel heating appliance this will offer a carbon positive benefit relative to electric heating. This saving will allow economies in other aspects of construction, such as thermal insulation requirements and glazing specifications.

■ A correctly specified flue will enable the use of a choice of heating appliances - allowing the builder to offer alternatives to the purchaser and so enhancing the bespoke element of the property.

■ Chimneys and the 'fireplace' remain a highly desirable aspect of the home with much documented evidence of their appeal to the purchaser from an aesthetic, lifestyle and comfort viewpoint.

■ It is wise in any property to have the option to burn fuels other than gas and electric, given the possibility of disruption to these supplies periodically and growing concerns about the long term security of supply as resources dwindle.

■ The use of natural draught flues, in conjunction with appropriate appliances, represents the sustainable option.

Chimney Specification

With open fires the requirement was to build chimneys with diameters greater than 200mm.
Modern appliances can operate effectively with flues of diameters less than 200mm. This is advantageous as the assumption in the SAP calculation is that a flue with a diameter of less
than 200mm reduces the natural or 'standing' ventilation from 40m3/hour for a chimney to 20m3/hour for a flue.
Significantly a ventilation rate of 40m3/hour is assumed for flueless gas fires so these offer no
benefit relative to a natural draught flue.

Appliance choice

All of the following can normally be accommodated.

OPEN FRONTED
Convector, wood and multi-fuel burners
Open fronted shallow bed fuel effect fire (ILFE)
Open fronted deep bed gas fire

GLASS FRONTED
Inset cassette fires (wood, gas or multi-fuel) Stoves (wood or multi-fuel, also known as dual fuel)

Carbon benefits of glass and open fronted fires

The graph below shows the carbon benefit of different types of open and glass fronted appliances, relative to the default electric secondary heating option. The values shown are for a typical 100m2 detached house.