Boarding out garage roof space

[Kipster]

I am looking to board out the loft space in my detached garage and before I do I guess I am looking for some reassurance that what I have planned isn’t a dumb idea!

It’s a modern build (1990ish) detached garage with an apex roof. In the center of each side wall is a single brick pillar that stops 2 inches below the rafters. The span across these is 2.5m. I intended to cross this with 2 lengths of 4 x 2 ( 2 high, 4 wide ) and then run 4 x 2 from front to back (off the same supports as the current roof structure) across this to form new rafters that are 1 inch above the current rafter that support the roof . I would then board over these so all the weight of the junk I have to store is not carried by the roof structure.

Well is it a dumb idea? And will the two 4 x 2 supports across the middle be sufficient?

 

[noseall]

for a true load bearing element you would need to use min 150x50mm joists.

 

[Static]

What does the existing roof do at the moment? why not just double up the ceiling rafters and lay boarding over? what size are existing members? photos?

 

[Kipster]

Thanks for the replies.

The existing structure just holds the roof tiles up. Its a triangular construction (like the one shown here http://www.acrooftrusses.co.uk/truss/truss.htm) and the rafters are 35mm x 70mm.front to back is in 2 pieces joined about 75cm from the center of the span. I'm just worried that any excess weight on this won't do it any good. That said there is not going to be anything of great individual weight up there just lots of it!

I was planning on using the 4 x 2 timber as I can get it for free as my brother has a load of 3m lengths left from a job he had planned!

 

[noseall]

if the storage stuff is fairly light weight, then go with static and double up.
if you then disperse the weight with some 600x2400x18mm t&g chipboard sheets, you should be ok.

 

[Static]

Go for some 47x145 joists running alongside the existing ceiling joists then span some boarding over and it will be suitable for supporting people/storage.

 

[Kipster]

Thanks for the advice, work starts this weekend.