Building regs - Part L
Building Regulation Part L was introduced in the year 2000, to bring about control for the Conservation of fuel and power. The latest revision came into effect on 1 October 2010.
The energy efficiency of a building is usually calculated using specific calculation software, such as the Simplified Building Energy Model (SBEM).
Using input data for the overall building design and specific elements of the construction SBEM calculates a carbon dioxide emissions rate for the building. A Rooflight is not a Thermal Element of the building, its’ U-value will always be higher than that of the surrounding roof, however, it helps to reduce the energy consumption of the building by reducing the need for artificial light and providing heat to the building by solar gain.
SBEM recognizes these advantages and offsets them against the heat loss factor to give an optimum quantity for rooflights at 20% of the floor area.
Part L1A - New buildings that are a dwelling*
The U-Value requirement is 2.0 W/m²k
The Air Permeability requirement is 10 m³/h.m² @ 50 Pa
Consideration should be given to limiting the effects of Solar Gain during the summer months
Part L1B - Existing buildings that are a dwelling*
The U-Value requirement is 1.6 W/m²k
Part L2A - New buildings other than a dwelling*
The U-Value requirement is 2.2 W/m²k
The G-Value guideline is: for each building space that is either occupied or mechanically cooled
if 10% glazed – G-Value guideline 0.68
if 20% glazed – G-Value guideline 0.46
The Air Permeability requirement is 10 m³/h.m² @ 50 Pa
Part L2B - Existing buildings other than a dwelling*
The U-Value requirement is 1.8 W/m²k
*Dwelling means a self contained unit designed to accommodate a single household. Building exclusively containing rooms for residential purposes, such as nursing homes, student accommodation and similar are not dwellings.
Note that larger extensions to existing buildings, where the total floor area of the extension is greater than 100m2 and greater than 25% of the total floor area of the existing building, are treated in the same way as new build and fall under the control of AD L2A.
