L1B SAP calculations conducted by experienced assessors. 

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Extension SAP calculations

Extension SAP calculations - L1B

Extension SAP calculations need to be completed on a building extension that has glazing for more than 25% of the floor area.


On completion of your SAP calculation you will receive and EPC certificate showing you have complied with building regulation and have passed part L1B of building regulations.

What our SAP assessors need from you:

Drawings (For proposed and existing dwelling) :

Elevation, Section Drawings 

Floor and Site Plans


Windows (Frame material, width of Gap, emissivity of glass)

Doors (Frame material, width of gap)

Heating and cooling

Ventilation system

Hot water system (Cylinder size and controls)

Extension SAP calculations explained  


The carbon output is increased where there are areas of extensive glazing. This is due to heat the increase in heat loss. To counteract this increase in carbon output and reduce any unnecessary heat loss, certain building alterations can be implemented. 

Installing solar panels to the exterior of the building could be used as an example of a method of balancing out the increased carbon loss. This modification to the design of the proposed extension would provide enough remedial work to pass the SAP calculation.

With multiple years of combined experience dealing in SAP extensions, our assessors will be able to provide you with the most cost effective and time saving approach to passing your SAP calculation. 

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