Indoor flat roof

[stric]

Anyone help?
I'm about to take on building an indoor office inside a factory, I'm using upvc sections and planning on fitting a timber flat roof because they would like to sound insulate it afterwards. I will put wall plates along the top edge of the units and a wall plate along the block wall at the back, it is a 4m span between the two, my questions are:
what size timbers should I use for the wall plates
what size timbers should I use across the 4m span
At what centres should I space them out
I will be fitting ply sheets onto the timbers.
Thanks in advance, I am a chippy but never done any roof work of any description

 

[noseall]

100mm x 75mm, for the wall plate, 195mmx 47mm, for the joists and set them at 450mm centres.

 

[splinter]

Might as well do 400mm centres ,they will work out right for the length /wide of the ply sheets

 

[masona]

what size timbers should I use for the wall plates

Normally the same width of the wall thickness.

 

[stric]

Thanks all,
Though I didn't explain myself too well, I called them wall plates but they won't be on a wall, one will be directly onto the tops of the upvc sections (as it is all upvc) and the back timber would be bolted to the rear block wall (not sitting on a block wall). but I'm guessing the mentioned sizes will still be okay
I was originally thinking of 150mm x 50mm 'plates' with 195mm x 50mm joists @ 600mm centres, is that not recommended
will it depend on the ply thickness

 

[noseall]

make sure you have ally reinforcing in some of the upright upvc sections. i guess you will need something like 75mmx75mm as a bearing plate on top of the upvc, and 150mmx50mm wall plate bolted every 600mm at tuther end sounds fine. i guess you will be fixing joist hangers to the wall plate then?
600mm centres on the joists might be stretching it a bit. i would buy a couple more joists and go with the 400mm centres for peace of mind.

 

[stric]

Thanks Noseall.