Velux rooflights and window openings

[eandg]

Is it just your standard 10mm all the way round for your Velux window openings or something different? I've allowed 50mm additional (width) and 45mm (height) as per fitting guide but cant' really see any benefit from the additional gap (or find anyone who seems to do this going by screwfix forums and the like). 

Edited January 10, 2022 by eandg

[nod]

10 mil is fine 

[Hobbiniho]

depends if you are going to be fitting the BDX insulation collar or not as the collar needs more room to install

[Thorfun]

just a word of warning for Velux windows, the lead time is currently 8 weeks for some windows! we got stung by this and with the shutdown for Christmas we've now been waiting nearly 10 weeks for some of our windows and got told last week that there is an extra weeks delay.

 

so get them ordered early.

[Radian]

How are you setting the top and bottom of the reveal? A pet peeve of mine is that it seems standard to set them perpendicular to the plane of the roof/window, like it might seem natural to a chippy to trim square between rafters. But, depending on height of window, when finished this can steal precious light as we found:

 

 

I altered the top trimmers of the two leftmost windows to make them horizontal - compare with how it looks against the one on the right which was yet to be modified. 

[Simplysimon]

On 10/01/2022 at 09:21, Radian said:

I altered the top trimmers of the two leftmost windows to make them horizontal

and even better if the sides can be splayed as well

[Cpd]

I have done both, one I created a shelf as this looked better and was more functional as the window is quite low down, the others I have done to maximise light as they are higher, not seen them with splayed sides…. 

[Radian]

11 hours ago, Simplysimon said:

and even better if the sides can be splayed as well

Perfect for defensive balistraria ?

 

17 minutes ago, Cpd said:

I have done both, one I created a shelf as this looked better and was more functional as the window is quite low down, the others I have done to maximise light as they are higher, not seen them with splayed sides…. 

 

Yes, the most natural light value is obtained from windows that are relatively low down but I cannot see any advantage in not always doing it this way. The velux installation guide shows the aperture trimmed both horizontally and vertically but I bet 9 out  10 builders don't take the hint.

 

[eandg]

On 10/01/2022 at 09:21, Radian said:

How are you setting the top and bottom of the reveal? A pet peeve of mine is that it seems standard to set them perpendicular to the plane of the roof/window, like it might seem natural to a chippy to trim square between rafters. But, depending on height of window, when finished this can steal precious light as we found:

 

 

I altered the top trimmers of the two leftmost windows to make them horizontal - compare with how it looks against the one on the right which was yet to be modified. 

Thanks - a huge difference there. 

[PeterW]

+1 to doing this - splaying top and bottom adds significant light into a room. The only difference when they are low in a roof is that I make the bottom level as a cill if it is usable or if it is to be used as a fire egress window. 
 

 

[Radian]

I would have actually liked to make the bottom vertical to continue the low wall below but I was installing perimeter trunking so left it perpendicular to match the plane of the sockets (yet to be fitted in this photo...) In an ideal world I would have liked another 100mm on the height of the windows to bring it all the way down but getting these kind of details right from the get-go is virtually impossible.

 

[eandg]

On 10/01/2022 at 06:25, nod said:

10 mil is fine 

Do you have any advice on detailing install for airtightness, insulation etc? Joiners doing this rather than the window fitters who'll come later and I think I'll need to spoonfeed them. 

[Dave Jones]

if your making it a warm roof do not forget to seal it with a vapour control layer.