Hi. After lots of advice here I've decided to stick with Velux for my roof windows. I'm trying to position one of my windows  - RL04 - over the bed in our master bedroom but space is looking tight to the ridge and valley.  How close can I go? The window could be the MK08 (780x1400) or MK06 (780x118).  Note, I'm aware the structural opening is wrong - just caught that mistake!  Should be width +60, height +45.   @JohnMo I feel certain you know the answer to this one! 

Sorry - unfortunately no real answer from me.

Only things that come to mind are

 

Ridge valley likely to be leaded, so you need room for that.

 

Slates or tiles, the first one below the velux and at the valley will need enough space so when cut it isn't to fragile. And has something to hang from.

 

The velux window will also have flashing this will need to be accommodated.

 

You need to think about the treatment inside the room where the Velux is so you get splays where and how you want them. We got ours so it was a direct drop down the walls - the wall goes straight up to the base of the frame but you might want a slope. Also don't forget that the flashing will have minimum dimensions. We have just one row of slates below ours before the hidden gutter.

Yep, splays are definitely an issue for us as the roof is 400mm thick.

@zzPaulzz I’m interested in what approach you plan to take with that.

Note that the lower splay results in reduced insulation at the base of the Velux so I’ll using extra low conductivity PIR here instead of the high pressure pumped cellulose. 

Thanks v interesting. I take your point about a bit of extra heat loss.