Dwelling extensions, and material alterations to form new dwellings

England and Wales - ADL1B

Sapper version 8 includes a unique facility for showing compliance with ADL1B for dwellings extensions. This is particularly useful for showing compliance for unseparated conservatories and other extensions using large glass areas.

First it is necessary to input just the details of the extension and the program will check for compliance with the Fabric Standards as Para 14, and the Comparative heat losses as Para 18. If this does not show compliance, it is then necessary to check for compliance using the method described in Para 20.

To do the Para 20 Check it is necessary to enter the details of the existing dwelling (extension details are already entered) and when these inputs are complete the software will check if the carbon emissions from the existing dwelling with the extension are no greater than the emissions from the existing dwelling with a 'notional' extension. The details of the 'notional' extension are calculated by the software from the input data.
Sometimes in order to show compliance it is necessary to include thermal improvements to the existing house as part of the project, e.g. a new Band A boiler or improved insulation.

Scotland - Technical Standards Section 6.2.9 - Extensions

It is only necessay to input the details of the dwelling extension area and heat losses'. The software will calculate the 'notional' extension details from the extension details.

Where the insulation envelope of a dwelling or building consisting of dwellings is extended, the area weighted average U-values of each of the exposed elements and the maximum values for individual elements should comply with the table in section 6.2.9
Maximum U-values for building elements of the building envelope (W/sq.m/K)
Type of element Area weighted average U-value of elements of the same type Individual element
Wall 0.27 0.7
Floor 0.22 0.7
Pitched roof (loft type) 0.16 0.35
Flat roof or pitched roof (insulation at rafters or roof with integral insulation) 0.2 0.35
windows doors and rooflights 1.8 3.3

The total area of windows, doors and rooflights in the extension should not be more than 25% of the extension floor area (plus the area of any openings which will cease to be exposed openings). The 25% may be varied if the compensatory approach is adopted.

Compensatory approach.
The U-values for the elements involved in the extension work may be varied provided that the area- weighted overall U-value of the all the elements is no greater than that of a 'notional' extension. The 'notional' extension should be the same size and shape as the proposed extension but with the elements complying with the above table and the area of windows, doors and rooflights being 25% of the extension floor area (plus equivalent area of 'built over openings')

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