SAP calculations for over-glazed extension

Project	Crest View
Client	L. Tann
Category	Extension

Overview

Our client was planning a single storey extension to her home, featuring full height bi-fold doors to maximise natural light and connect the indoor space with the garden.

The level of glazing exceeded the notional limit set under Part L1 of the Building Regulations, raising concerns about compliance—specifically the risk of excess heat loss and failing to meet the overall energy performance requirements.

To proceed with the design as intended, the client needed a SAP calculation to demonstrate that the extension would achieve an acceptable level of thermal performance, or to identify where compensatory measures could be made.

Our assessment showed that the client’s proposed U-values exceeded the minimum requirements set out in Part L. Using the whole-dwelling approach, this enhanced thermal performance was sufficient to offset the higher proportion of glazing. As a result, the client was able to proceed with her preferred design—retaining the large glazed opening, which was a central feature of the project—without the need for compromise.

Testimonial