Timber Roof Spans

[Mark-UK]

I am building a wooden shed measuring either 18' x 14' (5.4mts x 4.2mts) or it might end up being 19' x 15' (5.7mts x 4.5mts).

The shed will have a mono pitched roof.

I'm having a bit of difficulty finding the correct sizes to use for the roofing joists. About all I know is it has to be C16 and I want to have a 400mm span.

Could someone please provide me with the correct joist sizes I require for both sized sheds on a 400mm span?

Thank you

EDIT: I should add that the shed will be used for woodwork and that I may want to store some timber if I can fashion some sort of loft/storage space in the roof area (though this is by no means essential)

 

[Himaginn]

For ceiling joists, assuming spanning 4.2 - 4.5 metres 195 X 47 C16 but any storage requirements could affect this.



For rafters, again assuming spanning 4.2 - 4.5 metres .
nearest and best is: 150 X 47 C24, with 30° to 45° at 4.23 metres.

Otherwise re-think your design to use purlins, duo-pitched roof or flat roof.

 

[Himaginn]

For your ceiling joists.

 

[Mark-UK]

Thanks Himaginn!

Is a flat roof (with slight gradient for rain run off) the same thing as a mono pitched roof, or is it different?

 

[Himaginn]

I'm guessing because the tables only show sizes for rafters 15° and above.
So I'd say 0° to 15° could be classed as flat roof and 15° and above as pitched roof.

Flat Roof ‡ A flat roof is defined by having a roof pitch below 1.5 degrees or a Fall of 1 in 40 and can comprise of different products Pitched Roof ‡ A pitched roof is defined by having a roof pitch above 1.5 degrees or above Fall of 1 in 40. Construction materials will differ depending on the pitch of the roof. ± Standing seam roofs such as copper or zinc can be used over 1.5 degrees in pitch ± Traditional tile/slate roofs pitches start at 22 degrees but some manufacturers can reduce this to 12.5- 15 degrees.

http://www.airm.ie/system/download_images/53/original/GFF - flat Roof.pdf?1393261490

 

[Mark-UK]

That makes sense. Thanks Himaginn

I've another question I'd like to ask

I'm going to build a shed 18' x 14', but I might go for 18' x 16'. Will I be able to buy timber that's 16' in length? Or will I need to attach two pieces together?

 

[noseall]

That makes sense. Thanks Himaginn

I've another question I'd like to ask

I'm going to build a shed 18' x 14', but I might go for 18' x 16'. Will I be able to buy timber that's 16' in length? Or will I need to attach two pieces together?

4.8m is the longest standard length and is available at builders merchants and timber yards (not the sheds).
However, you can order specials at some remarkable lengths. We had some 7.5m fellas on a job once.

 

[Mark-UK]

Thanks noseall, much appreciated.