Advice on installing roof window please

[mersu]

Hi, I wanted to ask for your advice here on the forum. My roofer started building a wooden frame for a new roof window - pivoted Velux 2070. With the dimensions of 55x78cm it seems to me rather small and I would be interested in having a bigger window to provide as much natural light as possible. My builder is saying that the frame he constructed is of the maximum size possible without seriously changing structural parts of the roof. I'm not a specialist, but it seems to me that since the two rafters are already cut (see photo attached) that the size of the frame and window could be significantly bigger - or am I missing something? Advice appreciated!

[Big Jimbo]

Rafters should be doubled up either side of the roof window. That looks a bit rubbish to me.

[mersu]

  On 04/03/2020 at 18:52, Big Jimbo said:

Rafters should be doubled up either side of the roof window. That looks a bit rubbish to me.

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Thanks Big Jimbo!

What do you think about the size - could the frame and the window be bigger?

Edited March 4, 2020 by mersu

[Big Jimbo]

  On 04/03/2020 at 19:12, mersu said:

Thanks Big Jimbo!

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No problem, and the doubled up joists should be bolted together at 600mm centres

[Simplysimon]

bridles should be doubled up as well

[mersu]

  On 04/03/2020 at 19:18, Simplysimon said:

bridles should be doubled up as well

Thanks - the diagram is really helpful.
What do you think about the size - could the frame and the window be possibly expanded?

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[Declan52]

55cm is the smallest size most companies make but you can get them up to 120cm wide. 

Either your rafters are way out of square or his frame  work is.

As above the rafter should not have been cut without doubling up.

[Simplysimon]

for a dormer, up here at least, the max you can go is removing 4 rafters. don't know how wide you can go where you are without plannning for a window but that would give a nice big window without massively compromising the roof.

[PeterW]

  On 04/03/2020 at 18:40, mersu said:

Hi, I wanted to ask for your advice here on the forum. My roofer started building a wooden frame for a new roof window - pivoted Velux 2070. With the dimensions of 55x78cm it seems to me rather small and I would be interested in having a bigger window to provide as much natural light as possible. My builder is saying that the frame he constructed is of the maximum size possible without seriously changing structural parts of the roof. I'm not a specialist, but it seems to me that since the two rafters are already cut (see photo attached) that the size of the frame and window could be significantly bigger - or am I missing something? Advice appreciated!

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take it your roof isn’t square ..????

 

you could take out another rafter and then put new double rafters either side (needs it for strength) and then you really should have double trimmers top and bottom. 
 

what makes me wonder is how he’s managed to take those out without removing the tiles or the battens ..!! Need to also wrap the membrane into the frame. 

[mersu]

We agreed a new improved frame and a bigger window size - so everything resolved. Thanks for your help everyone!

[ProDave]

That roof is seriously out of square, what's going on?

[wozza]

  On 06/03/2020 at 18:23, ProDave said:

That roof is seriously out of square, what's going on?

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I agree, it doesn't look right.

 

Also has the roofer considered the distance from the bottom of the window to the top of the tile that sits under the window - it doesn't look right to me. 

 

Download the Velux fitting instructions and you will see what I mean - IIRC the bottom tile position in relation to the bottom of the window is more critical than the top (to get the window and flashing to fit correctly)

[Cpd]

It looks pretty terrible and the way the existing roofing felt has been badly ripped rather than cut is a worry, I like to leave a 25mm gap around the velux frame and the roof cut out and line this with PIR insulation, also as above the height and spacing in relation to the tiles is important.