Trimmers to rooflights

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i am looking to install a 3000mm x 2000mm roof light in my extension roof.

the roof structure is being cut in the next few weeks. should the trimmers around the roof light be double or triple timbers? I have seen both used but what dictates which to use?

 

[Notch7]

i am looking to install a 3000mm x 2000mm roof light in my extension roof.

the roof structure is being cut in the next few weeks. should the trimmers around the roof light be double or triple timbers? I have seen both used but what dictates which to use?

Trimmers don’t carry much weight generally - it’s the full length beams which carry the load -if you are referring to them then span and depth are key factors.

sometimes carpenters do double or triple joisting to match the beams - so doing the upstands ets is the same all round

 

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Thanks. The full length timbers are spec'd as 8x2's. Should i double these up?

 

[Notch7]

Thanks. The full length timbers are spec'd as 8x2's. Should i double these up?

It needs a structural engineer to advice really - hopefully Tony will see your post.

the total span is needed to answer.

 

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Span between the steels that the roof light sits on is 3.4m