Roof windows

[Carllongson]

hi hoping to do the roof on my extension next week. I'm planning to put a couple of velux windows in (lean too roof) is their any regs I should be aware of to how big the windows can be for roof size?

Thanks

 

[Nakajo]

Velux probably know a thing or two about this.

 

[catlad]

It would be a special case if you were being told what size windows you could have.
Don't you have drawings showing what sizes the
windows will be?

 

[noseall]

is their any regs I should be aware of to how big the windows can be for roof size?

Floor size/heat loss reg's - yes. The total amount of glazing within the building must not exceed 25% of the floor area.

Also, the width of the roof light will dictate the requirements for the trimmer rafters up the sides of each window.

 

[Notch7]

Floor size/heat loss reg's - yes. The total amount of glazing within the building must not exceed 25% of the floor area.

Also, the width of the roof light will dictate the requirements for the trimmer rafters up the sides of each window.

Yes, as Noseall says, if you introduce a glazing element, then you need to comply with building regs part L1b. The 25% rule is based on compliance with elemental values. However if you exceed the 25%, it is possible to gain compliance by having a SAPS test done. If the calcs dont pass then you would need to improve energy efficiency elsewhere to make up the difference. For example low energy light bulbs in the house, loft insulation or you may have had a new boiler recently that could count towards it.

 

[^woody^]

"Doing the roof" on an extension implies that is a new build and there would be plans and inspectors and stuff.