Shed Materials & Framing

Framing Systems

Portal Frame

The traditional industrial shed system. Large hot-rolled steel sections (typically UB or welded plate sections) form rigid frames at regular spacings (typically 6–9m bays). The frames resist wind loads through bending — the joints between column and rafter are rigid (moment-resisting), so the frame stays rigid without separate bracing in the portal direction.

• Best for: Large clear spans (18m+), high wind regions, heavy crane loads, industrial applications
• Advantages: Very strong, large clear spans possible, minimal internal bracing needed in frame direction
• Disadvantages: Heavy, expensive, requires welding (shop or site), longer fabrication time
• Typical spans: 12m to 40m+

C-Section / Cold-Formed Frame

Lighter cold-formed steel C-sections or Z-sections bolted together with gusset plates and bracing. The joints are pinned (not rigid), so the shed relies on a bracing system (tension rods, straps, or tube bracing) to resist lateral wind forces.

• Best for: Standard farm sheds, garages, workshops, hay sheds, storage sheds in non-cyclonic areas
• Advantages: Lightweight, fast to erect, no welding needed (bolted connections), cost-effective
• Disadvantages: Limited span capacity, bracing required in both directions, not suitable for heavy loads without reinforcement
• Typical spans: 6m to 18m

Structural Members

Columns

Carry all vertical and horizontal loads from the roof to the footings. Portal frames use UB/UC sections; C-section sheds use back-to-back or boxed C-channels. Column size is determined by the bending moment at the base (wind load × height) and axial compression from roof weight.

Rafters

Span between columns to support the roof. Must resist bending from wind uplift and downward loads (dead, live, stored). Portal rafters are typically UB sections with haunches at the knee (column junction). C-section rafters are typically paired C-channels.

Purlins

Run longitudinally between rafters, supporting the roof sheeting. Typically Z-sections or C-sections at 1.0–1.8m spacing. Purlins must resist wind uplift, dead load, and live load, and they provide lateral restraint to the rafter compression flange.

Girts

Wall members running horizontally between columns, supporting the wall sheeting. Similar sections to purlins. Girts resist wind pressure on the walls and also provide lateral restraint to the columns.

Bracing

Resists lateral (sideways) forces and prevents the shed from racking. Types include:

• Tension rod bracing — steel rods forming X-patterns in the roof and walls. Simple and effective.
• Strap bracing — flat steel straps performing the same function as rods. Common in lighter sheds.
• Tube bracing — RHS or CHS tubes for compression-capable bracing. Used where racking forces are high.
• Portal bracing — rigid frame bays in the longitudinal direction for larger sheds.

Connections — Where Sheds Fail

The most common point of failure in sheds is connections, not the members themselves. Every joint where one member connects to another must transfer the design forces through bolts, welds, or brackets. Under-designed connections are the #1 cause of shed failure in wind events.

Critical connections include:

• Base plate to footing — must resist uplift (holding down bolts cast into concrete) and shear
• Column to rafter (knee) — the highest-stressed connection in a portal frame
• Rafter to rafter (apex) — must transfer the roof loads across the ridge
• Purlin to rafter — must resist uplift forces from the roof sheeting
• Bracing connections — must transfer the full bracing force through the gusset plate

Frequently Asked Questions