Flat Roof Span 5.4m Joist Sizing

[jeds]

How about these monsters;

 

[Mr Chibs]

Not sure what they'll spec', but we once used these monsters on a 7m+ span...

Bigjoist1

• noseall
• 19 Nov 2018

440mm deep with 125mm top and bottom chords!

We use Posis on all our floors.

Out of curiosity, why are the 'monsters' sat on little block pad? instead of say a wall plate?

 

[noseall]

Out of curiosity, why are the 'monsters' sat on little block pad? instead of say a wall plate?

They're floor joists, awiting bricking in and building above.

 

[muh3]

Here a quick update.
Struktural Engineer wants £1200 to calculate, but that would include walls as well and technical drawings.
I got a calculation from a Posi Joist manufacturer near by, 600 center would be £1224, I guess 400 center would work out as £1632
I have now remodeled the shed a little, i was putting in a dividing wall half way through the building in joist direction, so i make that a load bearing wall and run the joists the other way. The span is now only 3.1m so 45x170 would be enough and the cost will only be about £440 with 400 center.

Thanks for all your suggestions.

 

[mrrusty]

Looking at that, why don't you consider using SIPs. https://www.simplysips.co.uk/pricing/ You can use them for both roof and walls and with 122mm SIPs @£90 there isn't much in it when you calculate the timber, insulation, sheet etc. I've just used them for a garden room - thread here https://community.screwfix.com/threads/garden-room.256842/

There's some useful tables for un-reinforced and reinforced flat SIP roofs here https://www.sipbuildingsystems.co.uk/pdf/SBS-Design-Guide.pdf

What I have learned about working with SIPs is that you have to be very accurate. Your base has to be perfectly level - there is nowhere to hide when you slot the panels together.