Approved Document L1B states that any extension can have an allowable glazing amount of 25% of the new floor area, plus the area of any openings being covered by the extension (i.e. the existing windows in the wall between the house and the extension). However, if you are planning an extension with glazing in excess of this amount, you can use SAP to justify your glazing by carrying out an assessment to show that the carbon emissions are no worse than if you had the allowed amount of glazing.
SAPs UK are experienced in proving compliance with Approved Document L1B through the use of SAP, and have never had an assessment not pass. We can provide advice on how to offset any additional carbon emissions and find a solution which works for you.
Glazing Assessments start at £125 per unit and are carried out in 2 – 3 days. The assessment is done from drawings and prices include notional and proposed assessments, and an explanatory report for Building Control.