Kitchen Extension - U-Value Calculation Floor Area

[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!

 

[Notch7]

If you are having an extension with excess glazing, a SAPS test will allow you to be compliant.

At worst you may have to make some energy efficiency improvements to the existing house, or if you have done any recently, they can be included. Even updating lighting to LEDs would help.

 

[dt25]

ok great i'll look into that test too.
Would you say then that the existing kitchen floor area can not be included in the total floor area calculation?

 

[tony1851]

In terms of glazing area in the extended part itself, you are normally allowed 25% of the new floor area, + the area of any windows or doors which no longer exist because of the extension. If you can keep within this area, you can use the normal elemental values for the roof, walls and floor.

If you want a larger area of glazing, you can do the 'area-weighted' calcs as described in Part L. What this entails is simply increasing the insulation value of the walls floor and roof to compensate for the loss through the additional glazing.

As a last resort, you can get a SAP calculation done, but these are usually done on spreadsheets and you would probably need to put this to an energy assessor.

 

[^woody^]

U value calculation?

Just put 80mm of celotex, 150mm of EPS, or 130mm of Styrofoam in it.

If you are saying that the area of new openings is greater than 25% of the new floor area minus existing openings covered by the new extension, then you need to be doing a SAP calculation instead.

 

[tony1851]

U value calculation?

Just put 80mm of celotex, 150mm of EPS, or 130mm of Styrofoam in it.

If you are saying that the area of new openings is greater than 25% of the new floor area PLUS existing openings covered by the new extension, then you need to be doing a SAP calculation instead.

 

[^woody^]

Yeah, lol.

 

[Dereekoo]

Google LABC "heat loss calculator" for spreadsheet for area weighted calculations