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U-Value Calculation Floor Area for Extension

Postby dt25 » Sat Jan 05, 2019 8:36 pm

Kitchen Diagram 2.jpg
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!

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Postby arbco » Thu Jan 17, 2019 7:34 pm

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.
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