Building Flat Roof

[Giant90]

Hello All,

I am building a workshop, the plan was for 8m x 5m which planning & building regulation granted permission. But would like to have more space and build it bigger.

The new plans will be for 10m x 7m.
I am stuck on the flat roof design, any advice is greatly appreciated.

How should I design the flat roof? Use RSJ? Span distance? Suitable size joist? RSJ? Max Centres? etc.

I did search the web and came up with I beam, JJI, Easy Joist etc but quotes came in at £1999+vat which is expensive for a workshop.

Original Plan:
Warm Flatroof - GRP>18mm OSB3>90mm Insulation>VCL>12mm Plywood deck>firring>75 x 225 joist>12.5mm plasterboard>3mm skim

Thank you,
Giant.

 

[catlad]

If you are looking to make it cheaper then you will need
a pillar in the middle.

 

[Notch7]

How about glulam beams?

90 x 405 has a loading of 2.4t UDL over 7m length.

2 glulams, 1 at 3.3m one at 6.6m. Then you could use 175 x 45 joists in between.

A 7m 90 x 405 costs about £250+vat

Im not a SE so above is just an idea, so its not professional advise.

The snow load on a 70m sq roof is a lot!

 

[noseall]

Easy Joist etc

We are currently using Posi-Joists on a 7.1m clear span and they are big bu££ers! 120mm top and botton chords and 421mm deep. £2880 all in for 15 units.

The blocks look tiny compared to the joists...…..
[GALLERY=media, 102135]Bigjoist1 by noseall posted 19 Nov 2018 at 10:07 PM[/GALLERY]

 

[Notch7]

top and botton chords and 421mm deep.

Sparkies dream doing the first fix.

 

[noseall]

Sparkies dream doing the first fix.

Correct. The void is huge. I tend to use them a lot and not for my benefit either.

 

[Giant90]

We are currently using Posi-Joists on a 7.1m clear span and they are big bu££ers! 120mm top and botton chords and 421mm deep. £2880 all in for 15 units.

The blocks look tiny compared to the joists

Wow that is a big joist, If there is no other alternatives I'll see what the best price I can get the joist for.

I did message a few SE but probably cheaper to use I beam jji etc.

Thanks for the picture it gives a good idea on the size.

Was considering low pitched roof but guess it will be as much.