Flat roof timber size

[Screech20]

Hey guys.

Im building my garage, and have just been thinking about the flat roof timbers.

I was planning on using 4x2 c16, but i'm not 100% sure if that will suffice.

The span is 3000mm, and they will be at 400mm centres.


Im governed by height, as it is going to be a warm roof, but the total height needs to be 2.5m, so the smaller the roof timbers the better, but i want it to be right!


Cheers

 

[munchingB]

are you using firrings to get a slight slope or are you cutting birds mouths in the rafters?

i wouldnt use anything smaller than 47x150 for a 3 metre span. 2x4 comparatively seems like it has the potential to fail which ever way you slope them. i think even with the 47x150 youre going to have to keep your birds mouths pretty small to get the best out of your joist depth.

i have a 3.2 metre span of 47x100 for my trusses on my pitched shed roof though i wouldnt like to hang off a single timber spanning that.

i think that the money you will save on buying smaller timber will cost you when you have to put twice the amount of noggins in to make it rigid that you may as well get the bigger 6x2s...?

 

[tony1851]

If you use 4x2 you will end up with a trampoline.
As above, use 6x2.

 

[themiddleagedun]

Or 7's

 

[Screech20]

Thanks for the replies.

Ill be using firrings for the slope.

Cost isn't an issue, it costs what it costs. The only issue is height.


Cheers.

 

[theoldun]

Span 3000. Imposed snow load 0.75kn/m2. Dead load maximum 0.75kn/m2 will require C16 47x150 @ 400 centres regularized to 47x145

Warm roof to garage is not required unless you intend to convert it to habitable use.
Regards oldun