Timber size to cover 12 foot width flat roof.

[BML]

I'm helping next door to build a garage with concrete blocks because I was a bricklayer. The garage is going to have a flat roof with a pich and its 12 feet wide. Next door reckons on using 2" X 6" but I think thats a trifle over the top.
Could someone please sugest what timber size he should go for.

 

[^woody^]

The garage is going to have a flat roof with a pich

2" X 6" but I think thats a trifle over the top.

How is it a flat roof with a pitch?

Anyway, 6x2 is actually under the top and you will need at least 7x2 at 400 c/c otherwise 8x2

 

[noseall]

Concur with Woodshaving, my calculator says 7"x 2" is a trifle lean by todays' standards.

 

[BML]

By flat I mean not with a gable and a ridge but flat with a drop of about 12 inches from one end to the other. I have to say I am suprised at roof timbers of 7". Its only going to carry roofing felt.

 

[joe-90]

It won't fall down with lesser timbers but it'll get a horrible bow in the middle.

 

[leew2]

According to the table here:
http://www.e-lindsey.gov.uk/NR/rdon.../0/014Flatroofstimbersizesandconstruction.pdf
you need at least 7x2 inch timbers at 450mm centres.
Of course your garage will most likely be exempt from building regs so you can use whatever timber size you want but be warned that using undersized timbers could cause the roof to bow and thus cause water to puddle on the roof and increase the chance of it leaking.

It may only be carrying felt most of the time but don't forget you could end up with a foot of snow on it which would add quite a bit of weight.

 

[^woody^]

Its only going to carry roofing felt.

No, the beams are made of timber not helium and don't just float there - they will sag under their own weight too