Glass amount regarding floor area

[Millwright]

Hi,

Can someone point me in the direction of the building regulation for a domestic dwelling regarding the amount of glazed windows/doors regarding floor area?

We're looking at an extension of 15.3sq M, french doors 1600mm x 2090mm and three windows, two at 1200mm wide and one at 700mm wide (may change to narrower) and all 1350mm high.

Any help appreciated. Thanks.

 

[tony1851]

Simple; you work out one-quarter of your new floor area (ie just the floor area of the extension), and then add to that the area
of any windows or doors which no longer exist because of the extension (or are covered up by the extension).

The resulting figure is the maximum area of new glaing you are normally permitted.

If your proposed glazing-area is above this figure, you can compensate by adding extra insulation elsewhere, eg in the roof.

 

[mfarrow]

In addition to Tony's post, which very much sums up the requirements, the regs also consider that anything 'considerably' less than 20% of floor area may make the existing parts of the dwelling too dark, and increase the use of unnatural light.

 

[Millwright]

Thanks for the information.

Would this glass allowance include the adding a window to the side of the existing property, in a room of which a window facing into the extension is to be removed and bricked up? Thanks.

 

[tony1851]

Thanks for the information.

Would this glass allowance include the adding a window to the side of the existing property, in a room of which a window facing into the extension is to be removed and bricked up? Thanks.

Even though it's put into an existing wall, the area of this window would still count to the maximum allowed.

 

[Millwright]

Here's a silly question.

Does floor area relate to the 'usable floor', or does it accout for entire area including thickness of walls? I'm hoping thickness of walls. It's a possibility, as of course building U values will include the walls.

 

[freddiemercurystwin]

I've always done the calc on the basis that the floor area is on the inside of the exterior walls ignoring any internal walls.

 

[mfarrow]

It's a possibility, as of course building U values will include the walls.

I don't really understand this bit?

 

[Millwright]

It's a possibility, as of course building U values will include the walls.

I don't really understand this bit?

Walls have U values too, so that would be taken into account regarding heat transfer.

 

[tony1851]

It's a possibility, as of course building U values will include the walls.

I don't really understand this bit?

Walls have U values too, so that would be taken into account regarding heat transfer.

Are they asking for average ('area-weighted') U-value calcs?