New flat roof window

[joeandrews]

Untitled

• joeandrews
• 12 Jan 2011
• 1

Untitled

• joeandrews
• 12 Jan 2011
• 1

Untitled

• joeandrews
• 12 Jan 2011
• 1

I'm about to install a new Velux window into a flat roof.

Please see my proposal, does this look okay? Will one new joist (running across the room) be enough, or should I put two joists fixed together to give it extra strength.

Many thanks.

 

[RedHerring2]

The rule for velux windows and rafters is:
Take out one or two, insert two, one either side (doubled up with originals)
Take out three or four, insert four, two either side.

I'm assuming the same applies to joists.

 

[joeandrews]

Thanks RedHerring2.

I'm happy to go with that rule, better to be safe than sorry.

Does that mean I should put 2 new joists together (where I was going to put 1 new joist), and then fix another new one to the extg joist at the opposite side of the opening?

 

[Static]

Does that mean I should put 2 new joists together (where I was going to put 1 new joist), and then fix another new one to the extg joist at the opposite side of the opening?

Yes

 

[joeandrews]

Untitled

• joeandrews
• 12 Jan 2011
• 1

Each joist has another peice of timber fixed to the top of it, this is thicker at one end and narrows off (obviously providing a fall for the flat roof).

Do I also have to fit a peice of timber to the top of my new joists?

Thanks again.

 

[RedHerring2]

You might not need to. These wedge shape timbers, furring strips, I think they are called, are to support the roof panels and to provide the slope for run-off. Assuming that the furring strips are still in place above and below the new windows, on the remaining parts of the joists, my guess is that there will be enough support for the roof panels.

If it is reasonably easy to provide an additional furring strip to the top of one of the new joists that you are inserting, then do so. Not to the new joist that is being doubled up to an existing joist, but to one of the other new joists. This may also help with fixing/supporting any flashing to the windows.

Also fit a piece of timber across the top of the stretchers to support the roof panels, above and below the windows, unless the strechers are positioned to support the roof panels anyway. But then you may need something across the bottom to support any plasterboard.

The point of these new pieces of furring strips are two fold:
To provide support if anyone is on the roof for maintenance, preventing damage to the roof panels, and
To provide longterm support to the roof panel to prevent sagging and ponding ocurring.