Which timber size for tie and rafters?

[forestboy]

Hi,

I'm building a shed/workshop out in the wilds, and want to use single roof type construction with no ridge board. I will use 18mm ply to cover the roof.

Anything overly complex will be a major headache as there is no access for machinery and it all has to be made and fitted by hand. Premade trusses would not be an option for instance because of the lack of access. Even getting scaffolding in would be an issue.

The span will be 12' (external) and 11'4" (internal).

Is it feasible for me to use a single tie/ceiling joist to bridge this? If so, what would the minimum size be? I'd be fixing a lightweight ply to underside and insulation above.

Thanks for any help you can offer.

 

[DAZB]

Have a look at the tables in here :

http://www.haringey.gov.uk/trada_span_tables.pdf

It starts at Section 4.2 on page 19 for ceiling joists.

 

[forestboy]

That is a very useful link, it's a bit confusing to a non-professional but it looks like I'll have to use 2x6.

Do you think I should keep 2x6 for the rafters as well? the tables suggest 2x4 would be OK. Can you mix and match like that?

Cheers.

 

[DAZB]

I won't make any difference if you use smaller section for the rafters. As long as it is within the recommended ratios then it's fine. Even if you were using concrete roof tiles the 2 X 4 rafters would cope so not a problem.

 

[forestboy]

That's very helpful, thank you.

 

[DAZB]

Your welcome and good luck with your roof.