Velux in extension enquiry

[j1977]

Hi all,

I am replacing the lean to roof on my house extension, to create a vaulted ceiling where the ceiling follows the rafters and I want to install 3 or 4 velux windows. Pitch of roof around 15 degrees.

I was looking at 600mm centers on 47x175 rafters so I could fit 55x118 velux windows between. But I'm now a bit confused as after speaking to velux, as they say the window will not fit with 600 mm centers. They say the window frame requires 40-60mm gap between the frame and rafters, for flashing, insulation etc, and if this is not the case, there is no guarantee on windows, issues with insulation etc.

Can anybody give me any advice please?

Thanks

 

[ree]

I've not read the MI's for this frame but, typically, an approx 20mm gap all around the frame is sufficient for a Velux.

Cant you simply space the trimming rafters out a little to give the Manufacturer desired opening? Set the header and sill with the same gap.

 

[j1977]

Hi Ree,

The total 40-60mm required applies to both sides so 20-30mm required on either side of the window frame.

I have thought about trimming the rafters but 47mm are what my building control require for the clear span of 3m. However they are also insisting on doubling up on the rafters either side of the windows despite velux weighing less than the tiles etc, so maybe that would give me some leeway.

I would need 590mm (window width of 550 + 20mm either side). With 600mm centers I have 553mm between rafters so i guess would need to find 37mm i think, so that is a fair chunk if im working this out correctly. Ideally would want to avoid doing this

Thanks

I've not read the MI's for this frame but, typically, an approx 20mm gap all around the frame is sufficient for a Velux.

Cant you simply space the trimming rafters out a little to give the Manufacturer desired opening? Set the header and sill with the same gap.

 

[ree]

"Trmming rafters" are the rafters that go either side of the frame - nothing to do with shaving off 20mm or 30mm.
Simply leave a space of 600mm between these trimming rafters.

Doubling up on trimming rafters (or floor joists or stud framing) is most always called for when cutting or leaving an opening. The frame is not structural.

Screw everything - dont use any nails.

 

[j1977]

Sorry was confused. I understand what trimming rafters are, was just not thinking to move them so there is a 600 gap between them. Will check with building control as they specified 600mm centers but hopefully shouldnt be a problem

Many thanks

"Trmming rafters" are the rafters that go either side of the frame - nothing to do with shaving off 20mm or 30mm.
Simply leave a space of 600mm between these trimming rafters.

Doubling up on trimming rafters (or floor joists or stud framing) is most always called for when cutting or leaving an opening. The frame is not structural.

Screw everything - dont use any nails.