Flat roof Construction.

[jassdhali]

Guys,
Replacing garage flat roof as its leaking and has pretty low head height.
It is 4.8 x 2.4 metres. Was looking at all joists as 4' x 2' (including wall plates).
Securing wall plate with M10 x 100mm expanding bolts and timber to timber joist hangers.
Joists at 400 mm centres.
What size joist hangers would be suitable?
What spacing should I generally have for the M10 bolts securing the wall plate, as I was thinking approx 300mm
Also as I would like to have the slope to drain water to front of house need to know what I could use as I unable to use 'firings' if thats how there spelt.
Thanks
I will be putting in a building notice, but would like to confirm all this before I do, I will be doing all this myself.

Thanks

 

[noseall]

4' x 2' won't cut it i'm afraid. You would need 5' x 2' minimum and i'm not sure whether this would satisfy the latest reg's as the trada tables have gone silly.

Fix wall plate at 600mm centres or between every other joist spacing. We tend to fix the plate with screws first then bolt after fixing the joists to avoid joists clashing with the bolts.

Jiffy hangers will do fine.

Why can't you use firrings/diminishing strips?

 

[jassdhali]

Noseall,
Thanks for reply, I will check with LABC to confirm joist sizing to be sure (no offence)

I wasn't sure how to fix the firing, but after reading flat roof section in Building Construction Handbook which was recomended on earlier posts ( poss by you) I understand I can still use them on the joist to create the slope, for front to back slope (for 4.8m span)

 

[jassdhali]

Just rang BC, they said 5 x 2 is on limit of span for 2.1m.
So I will need 6 x 2

 

[Static]

Just rang BC, they said 5 x 2 is on limit of span for 2.1m.
So I will need 6 x 2

Hmm.. only if the joists are at greater centres than you said.. 5x2 at 400 c/c can span 2.43m .. 2.65 if you go for C24 joists..
Unless you use the flat roof as a balcony..

 

[jassdhali]

Appreciate what your saying static, but as its gonna be approved by BC have to go with their recomendation.
Presumably I will have to use straps on the wall plate that will be resting on the brick wall on the other end of the roof, every 1.3m, looking at older posts?