U-Value Calculation Floor Area for Extension If you want to know how your DIY projects could be affected by building and planning regulations, click here to post questions and view answers

[dt25]

Hi all!
I've got a question regarding calculating the u-value for a new kitchen extension.

I am looking to build a single storey pitched roof extension onto a single storey house.
It will have bi-fold doors and roof lights.

There will be 2 existing windows removed to create the openings to connect to the existing kitchen room, so it will effectively be one single room.

My question is... for the U-Value calculation, can I include the existing kitchen floor area in the total floor area calculation? Or do I only use the extension floor area?

I've attached a plan diagram to explain.

Thanks in advance for any advice!

Read more: https://www.diynot.com/diy/threads/kitc ... z5blf3OarD

[arbco]

You can only use the extension floor area unless you do a SAP which will consider the whole house. In simple terms the rule the glazing should not exceed 25% of the extension floor area but you can add any existing glazing covered/removed as part of the extension to the allowance. You could also investigate an area weighted U value calculation or failing that a SAP if these do not work.