Purlins are supported by both rafters or building walls when laid horizontally. As a rule of thumb, purlins are frequently proportioned for a depth-to-length ratio of 1/32. Higher-grade steel purlins have higher yield strengths, indicating good strength and load-carrying capacity. GI purlins may be more overpriced due to the additional cost of the galvanization process. HR purlins are often more cost-effective initially, but long-term maintenance costs should be considered if corrosion protection measures are needed.

Purlins are supported by both rafters or building walls when laid horizontally. As a rule of thumb, purlins are frequently proportioned for a depth-to-length ratio of 1/32. Higher-grade steel purlins have higher yield strengths, indicating good strength and load-carrying capacity. GI purlins may be more overpriced due to the additional cost of the galvanization process. HR purlins are often more cost-effective initially, but long-term maintenance costs should be considered if corrosion protection measures are needed.