Start with the roof, not a beam depth
We cannot settle a choice between 450 mm and 750 mm beams from the span alone. The designer needs the actual beam system, covering, support conditions and exposure.
Products of similar depth are not necessarily interchangeable. We work from the manufacturer’s data for the equipment proposed.
What changes as the span increases?
As clear span grows, bending and deflection become more significant. A deeper beam can often provide greater stiffness and capacity, but that does not mean every large roof automatically needs the same beam. Beam make, section, connection details and the overall frame arrangement need to be checked together.
Temporary roofs may also include paired beams, trusses, intermediate bracing, tracks, ridge details and proprietary roof systems. Comparing beam depth without the rest of the design can therefore be misleading.
Wind can govern the whole structure
The roof covering attracts wind pressure and suction. Depending on geometry and exposure, uplift can become a major design consideration. NASC temporary-roof guidance highlights the need to consider the roof and support scaffold together, including uplift, overturning and side sway.
A deeper beam does not remove the need for adequate ties, anchors, kentledge or support-scaffold stability. The loads still have to reach the ground or supporting structure safely.
Check the supporting scaffold too
A beam choice does not resolve the supports underneath it. Tie restrictions or limited foundation positions may drive the roof layout as much as the span. We need those conditions in the brief.
Decide on the covering early
Tell us what covering and side enclosure the job requires. Changing that later can mean revisiting the design. Installation methods and openings also need to be understood before selecting the roof arrangement.
Work out how it will be built
We look at assembly space and lifting access with the designer. A larger preassembled section is only useful if the site can accommodate its assembly and lift.
We consider the strike too. The site may be very different by the time the roof comes down.
What we need to assess the roof
Send roof dimensions, building information and the work sequence below. Mark support or tie restrictions and tell us what crane access is available.
We can then develop the brief with the designer and make the pricing assumptions clear.
Let the design determine the beams
Specify what the roof has to do and the conditions it has to work within. Beam selection follows from that assessment. We can then price an arrangement that suits the work and can be erected on the site.
Further reading
Related access: Temporary roof scaffolding.