Building roof- space for velux?

[Ican76]

Hello.
I am currently having a single story extension built and will be building the roof myself.
It will be a lean to roof and I am fairly confident Doing the job, even though it will be my first time! As you can imagine I have loads of questions, so here's one of them.

I intend to fit velux roof windows and understand that the timber needs to be doubled up around them.
What I'm not sure about is the size of the opening i need to leave? And weather the velux are screwed directly into the joists or into the slats that will run horizontally across them?

The window I want to fit is 114cm x 118cm. Do I build the roof with a much larger space for windows, then fine tune with slats, or is there a set number of mm larger than the window that I should leave around the window space when building the roof?

Any help would be much appreciated, thank you.

 

[catlad]

To get the most light out of your windows you need to
splay the reveals, all the information is available on the
velux web site. The window fits on the batons and you generally leave a baton width all round the frame.

 

[Ican76]

Thanks for the quick response. Will check their site out .

 

[noseall]

You need to fit a dedicated top and bottom fixing batten as per Velux instructions. These batten positions are determined by measuring from the top edge of the last (bottom) course of tiles before the intended roof window location.
Everything is measured off this. Keylite Windows vary slightly but the principle is the same.

 

[Ican76]

Thanks noseall.
I was intending to build the roof, fit the velux and then tile it ,
So as it's not built yet I have no tile to take measurements/reference from!

Is this wrong? Do I need to tile it first, then fit the windows?

Thanks

 

[noseall]

You don't necessarily need to tile the roof, no.

When building the roof, you set out your rafters and doubles so that you will have your roof lights' lateral position determined. We then hold off fixing the top and bottom trimmers until we have set out the roof tile battens.

Once you have a few courses of tile batten fixed, you can then determine accurately where the final position of the roof light will be in terms of height up from the plastered internal wall. Logic would suggest not too high up as to be practical. You can soon (temporarily) pop a tile onto the batten and measure off this, so as to determine the top and bottom roof light fixing batten position.

You can then fix the top and bottom roof light trimmer accurately.

 

[Ican76]

Fantastic explanation. Much appreciated mate.

No doubt I'll have a load more questions but that gives me a clear idea in my head to be getting on with.

Thank you.

 

[tony1851]

Depending on what size rafters you are using, you may not need to double up; often a waste of time and money.