Estimation & Costing for Pre-Engineered Buildings: Steel Frame to Cladding

Pre‑Engineered Buildings (PEBs) offer speed and cost savings by fabricating structural components off site and assembling them quickly on site. Accurate estimation and costing are vital to ensure these benefits are realized without cost overruns.

Who this helps

This post is for quantity surveyors, estimators, project managers and site engineers involved with PEB projects. It explains how to quantify and price each component of a metal building, from the steel frame to the cladding and accessories.

Foundations

A PEB system consists of primary framing members (columns and tapered rafters), secondary members (purlins, girts, eave struts), bracing systems and accessories such as doors, windows and insulation. Cladding for the roof and walls is typically profiled steel sheeting with insulation layers. Design standards may follow IS 800 or MBMA/AISC codes depending on the region.

Step‑by‑Step Quantity Take‑Off

1. **Gather design drawings**: Obtain general arrangement, anchor bolt plans, roof and wall sheeting layouts and connection details.

2. **Primary framing**: Measure the lengths and count of columns, rafters and beams. Calculate steel weight using the manufacturer’s section tables (weight = length × unit weight).

3. **Secondary members**: Quantify purlins and girts by counting the number of bays and spacing. Multiply lengths by unit weight per meter.

4. **Bracing and anchorage**: Measure rod bracing lengths and count anchor bolts, base plates and connection plates.

5. **Roof and wall cladding**: Calculate surface area of roof (plan area / cos slope) and walls (length × height). Include allowances for overhangs and end laps.

6. **Insulation and accessories**: Estimate insulation area (same as cladding area) and count accessories such as doors, windows, ventilators, skylights and gutters.

7. **Erection and bolts**: Quantify the number of high‑strength bolts and nuts required for connections. Include erection equipment and labour as a separate line item.

Example BOQ for a PEB Warehouse

| Item | Unit | Quantity | Rate (INR) | Amount (INR) |

| --- | --- | --- | --- | --- |

| Tapered Columns | tonne | 25 | 85,000 | 2,125,000 |

| Tapered Rafters | tonne | 28 | 85,000 | 2,380,000 |

| Purlins & Girts | kg | 15,000 | 75 | 1,125,000 |

| Bracing Rods & Plates | tonne | 3 | 85,000 | 255,000 |

| Roof Sheeting (0.5 mm) | sq m | 3,500 | 650 | 2,275,000 |

| Wall Cladding (0.5 mm) | sq m | 2,800 | 650 | 1,820,000 |

| Insulation (50 mm) | sq m | 6,300 | 120 | 756,000 |

| Anchor Bolts & Fasteners | lot | 1 | 400,000 | 400,000 |

| Doors, Windows & Louvers | lot | 1 | 350,000 | 350,000 |

| Erection & Commissioning | lump sum | 1 | 1,200,000 | 1,200,000 |

| **Total** | | | | **12,686,000** |

Formulas

- **Steel weight** = length (m) × unit weight per meter (kg/m) × 0.001 to convert kg to tonnes.

- **Roof area** = plan length × plan width / cos(slope angle).

- **Wall area** = perimeter length × eave height.

- **Insulation volume** = area × thickness.

India vs GCC

In India, PEBs commonly use IS 2062 Grade E250 or E350 steel and follow IS 800 or IS 875 for design loads. Labour costs are lower but logistics can be complex due to remote project locations. In the GCC, ASTM A572 or ASTM A36 steel grades are used, with design aligned to AISC/MBMA standards. High temperatures require thicker insulation and reflective cladding to minimize heat gain. Labour costs are higher, but site infrastructure and crane availability often reduce erection time. Always account for import duties and transportation costs when sourcing from overseas suppliers in either region.

Mistakes & Fixes

- **Ignoring connection weight**: Include plates, cleats and stiffeners in steel weight calculations.

- **Underestimating bracing and anchor bolts**: Count all bracing rods and anchor bolts; missing items lead to delays.

- **Misjudging roof slope**: Adjust roof area calculation for slope; using plan area underestimates sheeting quantity.

- **Overlooking insulation and accessories**: Budget for insulation, gutters, downpipes and flashing to avoid extras later.

- **Neglecting erection costs**: Include crane hire, skilled riggers and temporary bracing in the BOQ.

Mini QA/QC Checklist

- Verify vendor design calculations and drawings certified by a professional engineer.

- Check that steel grades meet project specifications and mill certificates are provided.

- Inspect fabrication quality: dimensional tolerances, hole positioning and welding quality.

- Confirm galvanizing or painting thickness as per corrosion category.

- Ensure trial assembly of critical connections before dispatch.

- On site, check anchor bolt positions and foundation levels before erection.

- Monitor bolt torquing and record tension values.

- Inspect cladding alignment, overlaps and fastener spacing.

- Test insulation installation for continuity and absence of gaps.

- Document all inspections and maintain a quality log.

FAQs

**Q: How is a PEB different from a conventional steel structure?**

A PEB is designed using standardized tapered sections and cold‑formed secondary members, allowing efficient fabrication and rapid assembly. Conventional structures use built‑up or hot‑rolled sections and are custom engineered, leading to longer fabrication time.

**Q: What design life should be considered for PEBs?**

Most PEBs are designed for a 25‑50‑year service life depending on usage and maintenance. Proper corrosion protection and periodic inspection extend the lifespan.

**Q: Can PEBs support heavy overhead cranes?**

Yes, but the crane loads must be considered during design. Crane beams, columns and bracing need to be sized accordingly, and additional costs for crane girders and runway beams must be included in the estimate.

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