The general approach of complying with Approved Document
L would be:
• Client briefs architects:
• Architects proposes
a building, carry out or commission a specialist to calculate the whole
building CO2 emission rate according to National Calculation
Methodology (NCM), and make sure the proposed building has an CO
2 emission rate (BER) less than the target CO2 emission
rate (TER), that is:
BER < TER
• Architect then specifies:
• The fractional area
and the g factor of the glazing, and
• The U-values of different
cladding zones, and the U-values of major components if necessary.
• Façade specialist
contractor then carries out the detailed designs to meet the specification
according to second tier document ‘The thermal assessment of
window assemblies, curtain walling and non-traditional building envelopes’
published by CWCT.
This approach gives great design flexibility in choosing
the U-value of components.
