Welcome to CalcTree's Purlin and girt design tool! You will be able to determine the member capacities for purlins and girts according to American Iron and Steel Institute (AISI) S100-16. The purlins are manufactured by AEP.
For details of how to design purlins and girts, check out our design guide here.
❗This calculation has been written in accordance with AISI S100-16
Typical purlin and girt steel sections

📝 Note



Purlin dimensions


Web thickness (D)

Flange Thickness (B)

Design thickness per nominal gauge

Span of member

Material properties

Yield stength, Fy (ksi)

Tensile strength, Fu (ksi)

Young's Modulus, E (ksi)

Shear buckling coefficient, Kv

Base steel thickness, t


Member capacities

Shear capacity

Moment capacity (kips*ft)

Axial compression capacity

Nominal tensile strength

If output values report "#N/A", you're input parameters do not match a section in the manufacturer's catalogue.


For details of how to design purlins and girts, check out our design guide here.
Here is a brief summary to get you up to speed:
  1. Purlins and girts are structural members used to support loads from sheathing and cladding in roofs and walls, respectively.
  2. The designer must consider various loads such as dead, live, snow and wind loads. Dead loads include the self-weight of the purlin or girt and superimposed dead loads, such as cladding, tanking, insulation, plaster, finishes, and services.
  3. Purlins and girts can be made from timber or steel, with steel sections being either C or Z-shaped and are usually cold-formed.
  4. The maximum distance between steel purlins and girts should be around 1200mm, with typical distances in residential buildings being about 600 or 800mm.
  5. The initial depth of a purlin or girt can be estimated by the span/32 rule of thumb.
  6. C-section purlins and girts are typically used in simple, non-continuous spans, while Z-sections are typically used in continuous lines of purlins for easy lapping at internal supports.

🎁 Bonus info


  1. Manufacturer's table: AEP:
  2. AISI S100-16 -

💬 We'd love your feedback on this template! It takes 1min