Velux Roof Windows in roof with no battens or felt

[stevemff]

Hi All,

As part of my own loft conversion that I'm slowly working my way through I have three Velux windows to put in. Although this will be the first time I've attempted to fit Velux I've done other windows and roof work so feel reasonably confident I can do it and its fun to learn new skills but I'm looking for a little advice as my roof differs in construction to all the official instructions.

I have a 1930's house with the original roof of clay tiles on sarking boards (well featherboards really but I guess they can be tapered too) nailed to the rafters.

So no battening and no roof membrane. Since all the instructions assume both of those things I believe I can skip a couple of steps but it would be great to get some guidance from those with experience.

My parts are:

GGL MK04 Solar windows
EDP Flashing kit
BDX Insulation collar

My questions are:

1) Given I have no membrane the underfelt collar seems pointless to fit, is there any downside I'm not seeing to leaving this out?
2) Similarly the drainage tray that is part of the BDX kit and goes above the window - Given I don't have battening this wouldn't fit under the tiles and would be counter productive with no membrane so I intend to leave this out. Any concerns?

I found THIS video very useful as it's a similar roof to mine and he has the same thoughts re. collars and drainage.

Any thoughts/advice gratefully received
Steve

 

[catlad]

Well he has batons which you said you don't so that's a bit confusing!
If you don't use the collars you will end up with cold reveals which aid condensation in cold weather. The BDX collar which you fit once the frame is in will help stop warm air condensing on the alloy flashing kit in cold weather.

 

[stevemff]

Thanks catlad, Yes I could have been clearer his roof was similar in the sense of the lack of roofing membrane rather than the battening.

So given your advice I'll install the underfelt collar's as per instructions to aid with the condensation and just leave out the drainage tray part.

 

[catlad]

Yes drainage tray will be redundant if you have no membrane.
I would still recommend using the BFX collar.