Structure materials
Painted Steel vs Hot-Dip Galvanised Greenhouse Frames
Frame corrosion protection is one of the cheapest specification decisions to get right and one of the most expensive to get wrong. The differentiator is zinc coating thickness and how the structure behaves in humid, coastal or fertigated environments.
Direct answer
What galvanising specification should appear in the RFQ?
State the standard and the coating mass, not just the word 'galvanised'. Hot-dip to ISO 1461 with a stated micron thickness, or pre-galvanised sheet at Z275 (275 g/m²) or Z600 for harsher sites, plus zinc-rich repair for all site welds.
| Dimension | Painted / pre-coated steel | Hot-dip galvanised steel |
|---|---|---|
| Frame cost per hectare | USD 90K–170K | USD 115K–220K |
| Corrosion life (inland) | 8–15 years with repainting | 25–40 years |
| Corrosion life (coastal / humid) | 4–8 years — repainting cycle starts early | 15–25 years |
| Coating standard to specify | Paint system to ISO 12944 category (C3–C5) | ISO 1461 hot-dip; or Z275/Z600 pre-galvanised sheet |
| Cut edges and welds | Must be touched up on site | Post-galvanised parts protected; site welds need zinc-rich repair |
| Maintenance cost | Repaint cycles, production interruption | Effectively none in the first 15 years |
| Fertigation / chemical exposure | Vulnerable where drips and salts collect | Tolerant; still specify drainage detailing |
| Financing / insurance view | Shorter assumed asset life | Supports longer depreciation and tenor |
Cost delta at a glance
- •Hot-dip galvanising typically adds USD 20K–60K per hectare of frame cost — roughly 3–8% of a turnkey greenhouse budget.
- •A single repaint cycle on a 1 ha painted frame costs USD 25K–70K including access equipment and downtime.
- •In coastal or high-humidity sites galvanising pays back on the first avoided repaint, usually within 5–8 years.
Planning-grade ranges for budgeting only. Actual pricing depends on site, specification, climate and supplier scope.
Choose Painted / pre-coated steel when
- Short-life or temporary structures with a defined decommissioning date
- Dry inland climates with low chloride exposure and disciplined maintenance budgets
Choose Hot-dip galvanised steel when
- Any coastal, tropical or high-humidity site
- Assets financed over 10+ years or carried at long depreciation
- Houses with intensive fertigation where salt exposure is continuous
Frequently asked questions
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