Rafter sizing for Velux windows

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sgg123
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Rafter sizing for Velux windows

Post by sgg123 »

Hello all,

Hopefully an easy one to answer.

I will be installing a couple of FK06 - 66 x 118cm Velux windows in a roof space. As per the structural engineers advice I have strengthened the roof rafters and added double trimmers above and below the proposed window spaces.

I have decided to set the top and bottom trimmers at exactly the same height dimensions as the window opening (see sketch attached), so the space between each set of double trimmers is 1225mm (1180 + 45mm) as per the Velux installation illustration - also attached.

My question is - is it OK to have the rafter trimmers at these intervals - or do they need to be further apart? The only issue I can think of right now is that this would force the window reveal splays to be at a right angle to the window rather than say spilling toward the floor. Is there any other reason why I should consider repositioning the trimmers?
trimmers.JPG
trimmers.JPG (58.83 KiB) Viewed 813 times
Velux size guide.JPG
Velux size guide.JPG (22.25 KiB) Viewed 813 times
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