GLAZING ADVICE
Is there a limit on the amount of glazing I can include in my extension?
This has become quite a common question for people looking to complete larger areas of glazing on their new extensions and refurbishments, particularly as people become more aware of sustainability and speci cally the thermal impact that glass can have on a space (and their heating bills).
Generally speaking, people are not looking for conservatories any more (which have a clear internal/ external delineation thermally with external-grade doors between the main building and the extension) and are looking for rear extensions with larger areas of glazing and connections back through to part of the whole of the remainder of the ground- oor plan. The glazing should be considered generally in terms of the layout and the direction the extension faces, alongside how much roof light may be required to try to get light into the newly darker central parts of the oorplan.
There is a rule of thumb in the Building Regs (Part L) that requires your building works to meet certain requirements, including a 25% rule of glazing to oor area, so if you build a 20m extension you can have 5m of glazing total across walls and roofs. This is, however, not very much glazing if you want to get some roo ights and a large rear opening, and is very restrictive if you’re looking to create something more interesting than a box with roo ights and windows.
There are acceptable approaches to achieving more glazing than this. The main aim of the regulation is to ensure we are not making buildings that are thermally inef cient and which suffer as a result of large glazed areas. The reality is that most people improving their homes are doing so in more than one way and, as such, the overall performance of the building is an improvement. This can be measured by means of a SAP calculation
— a process where a notional calculation of a typical situation is carried out compared to your proposals’ calculation to ensure that it performs more ef ciently.
Standard glazing can be improved upon in terms of U values to provide better performance by use of different types of double or triple glazing and various solar
lms and blind systems. Insulation can be added to walls, oors, roofs and other sustainable energies introduced — solar panels, air source heat pumps etc, and all of these combined can contribute to the increase in the overall thermal performance of the building.