About

Constructing roof frames from Rectangular Hollow Sections (RHS) or Square Hollow Sections (SHS) offers superior durability compared to timber, but introduces critical considerations regarding dead load. Steel structures exert significant weight on foundations; accurately estimating this mass is vital for concrete footing design. This tool sums the linear footage of the truss chords, webs, and purlins, then applies specific density factors to derive the Total Steel Weight.

Unlike wood, where waste is often usable scrap, steel fabrication involves "kerf" loss and non-reusable off-cuts. The calculator includes a Weld Allowance factor, inflating the raw material requirement to account for fit-up prep and consumption, ensuring you order sufficient stock lengths from the supplier.

Formulas

Total Weight (W_t) is the summation of all members multiplied by their linear density (ρ) and the waste factor (k):

W_t = (L_rafters + L_purlins + L_bracing) × ρ × (1 + k)

Reference Data

Profile (inch)	Wall Thickness	Weight (lbs/ft)	Metric Approx
2 × 2 SHS	1/8"	3.05	50x50x3 mm
2 × 2 SHS	3/16"	4.32	50x50x5 mm
4 × 2 RHS	1/8"	4.75	100x50x3 mm
4 × 2 RHS	3/16"	6.87	100x50x5 mm
6 × 2 RHS	3/16"	9.42	150x50x5 mm

Frequently Asked Questions

Steel is heavy. A simple 20x20 garage roof can weigh over 2,000 lbs just in framing. This dead load must be transferred to the foundation. If the foundation isn't designed for this specific point load, it can crack or settle.

For simple shed roofs, a 5% allowance is standard. This covers the material lost during saw cuts (kerf) and small off-cuts that are too short to reuse. For complex trusses with many angles, use 10%.

No. This tool calculates the *self-weight* of the structure and the material quantity. It does not analyze the structural strength or load-bearing capacity of the steel profile.