SAP For Overglazed Extensions London

Do you wish to make certain you get your over glazed extension recognized with creating management. We can assist you when you are over the permitted quantity of glazing. We can figure out the best way to achieve compliance with the building regs.

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Heat Loss Calculations

It’s now quite stylish for contemporary extensions to generally be bright and light and this is usually accomplished by having such things like bi-fold doors and large amounts of glazing. The downside is that these designs, although desirable, doesn’t fit well with the building regulations which aims to decrease heat losses from homes.

But don’t worry, you can find ways to have that modern design and ensure that the properties heat losses are not worse than the building regulations require. This can be achieved by getting an Assessor to produce Sap calculations but conforming to the building regs which states that the glazing needs to be:

  1. a) No more than 25% of the floor area : plus
  2. b) the total area of any doors or windows that are removed as result of the extension.

So for example if we have an extension with a total floor area of 10 m2, and we intend to take out the existing patio door of 4 m2 to produce an opening from the house to the extension. Then this is the maximum amount of permitted glazing.

Extension floor area10.0m2
25% glazing allowance2.5m2
Plus existing opening made by patio door4.0m2
Maximum permitted amount of glazing6.5m2


If you imagine a typical external door being around 2 m2, you will realise that 6.5m2 is not a lot of allowed glazing.

If you still desire that light and bright extension in London, you will have to demonstrate to building control that your proposed extension still is compliant with AD L1B. To do this you will need Sap calculations.

The Whole Dwelling Method

This technique allows greater design flexibility by using Sap calculations to show that the CO2 emissions from the entire dwelling including the overglazed extension are no worse than a ‘notional’ property of the identical shape and size with an extension having no more than the maximum amount of glazing.

This way upgrades in the original house for example wall or loft insulation, or home heating improvements can be done to overcompensate for the overglazing. If those improvements have been made already and are over and above that required by AD L1B then the property can be credited with this.

To be able to carry out the Sap calculations no site visit is called for, but we will require the following:

• Floor Plans to include sections and elevations
• Orientation of the property
• Construction specification of walls, roof and floors
• Specification for all doors and windows
• Primary and secondary heating
• Provision for providing hot water
• Information of renewable technology (if any)
We’ll additional assistance in supplying the required information.

So if you require a Sap Assessor or Sap calcs in or around London, then get in touch now.


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