Glass to Floor area percentage, for building regs
 

we've been told that you can't have more than 25% of GLASS area (not the whole window area with glass and frame... its just the GLASS area) to floor area.

Is this true, if so hows the best way to work it out so we know what size WINDOWS we can have for the new build extension..... and how big we can go with french doors too.






Phil

Seems strange Phil.

You see loads of builds with complete glass walls.

If true, calculate your floor space and divide by 4 for the glass. Any window manufacturer will then be able to tell you how big the hole in the wall has to be to accomodate the whole window/french door assembly.

Planning Portal - Approved Document F

Phil

It should be here. Start with Parts K and M. The glazing regs are a nightmare, particularly protection from falling, ventilation of habitable rooms etc. Have fun!

thats a rule of thumb for traditional cavity construction and can be overstretched with proper engineers detailing and proof that insulation requirements are not compromised (ie expensively)

mmmmmmm, so that could be the way round it then.



dave, thanks for that, I'll let Jo work her way through that lot. lol

Phil, it depends on the kind of glass. If you use more expensive glass with better heat insulating properties you can have more, but as said before the cost starts to rise alot.

You're allowed 25% of the floor area + any doors or windows that will be covered up / removed by the addition of the extension. There are a few trade offs that we will accept, for example if the existing house doesn't have cavity wall insulation and will have this installed at the same time as the works are carried out, or a heat loss calculation showing that increasing the insulation value of the other elements will contribute towards the increased heat loss through the glass.
Some glazing can be very energy efficient, but at a cost.

Approved Document L1B is the one to look at, paragraphs 14 - 20 give the guidelines, and show how to calculate area weighted values, which could get you through.

Pop along to the Council and have a word, we get lots of people asking similar questions. The overwhelming principle that we apply is that if it's no worse than it was previously, then it'll probably be acceptable.

:(

all seems complicated