DIY Doctor UK DIY Forums

Hi - I'm looking to put an extension (not conservatory) on the rear of my house, with quite a high quantity of glazing in it. I know Part L gives a limit on the percentage of glazing to the new floor area, but am told I may be able to increase this by providing higher insulation in the new solid walls and roof.

I have no training in this area - is anyone able to advise how this is done?

There are various trade offs within Approved document L1B which initially suggest 25% of the floor area glazing and then any openings that are covered may be added to this.

The other option is averaging U values and increasing other elements as you suggest.

Your best option though will be a SAP rating of the whole house plus the proposed extension compared to the house plus an extension which complies. Look at SAP rating on the web for help in this area.

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