Flat garage roof truss/joist

[kevtrydiy]

I am doing a diy build on a garage and need to know what size of joist/truss to use for the span width.
I have a span width of 5.2m to the outside of the brick for a 14ft door and the garage is 7m long door to the back.

I was told to put the joists every 600mm along the lenght of the garage.

Do I use 45x220mm as this will fit the height of a block in the wall when building or will I get away with a smaller size 45x150mm?

Cost aint hugh issue if the weight of the roof will be! But the cheaper I can get away with the better.

Cheers in advance.

 

[noseall]

5m clear span is quite a gap and would require some meaty joists maybe 225 x 50mm or even 250mm deep.

have you thought about using a piece of steel midway, thus splitting the 7m run in half?

 

[kevtrydiy]

Yeah I did think of that but havn't looked very far into it!!

Any idea if a 254 x 102 I beam would do? Or what would I need and then what size of timbers if the beam was taking the weight?

I have been looking at 45 x 220 whitewood regularised and treated C16 timbers if not using a steal beam.

 

[^woody^]

For a 5m span you are looking at 9x2 at 400 centres or 9x3 at 600 centres