Why asbestos cement roofs cannot receive solar PV
Three roof types are absolutely incompatible with solar PV in the UK: (1) Asbestos cement (AC) sheets — most common in pre-1985 warehouses. AC cannot be structurally loaded with PV mounting systems, and disturbance risks asbestos fibre release. No UK insurer or HSE guidance permits PV on AC roofing. (2) Asbestos insulation board (AIB) — rarer, pre-1975 buildings. Same restrictions. (3) Severely degraded bitumen felt or compromised metal decking. If your building has AC roofing, replacement is the only path to solar.
Combined re-roof + PV specification
Standard specification: structural assessment for PV live load (typically 25-40 kg/sqm — most portal frame buildings have headroom). Re-roof: profiled steel standing seam or trapezoidal cladding (Kingspan, Tata Steel, Hadley) compatible with solar mounting clamps. U-value: 0.18 W/m²K minimum (MEES/Part L). PV mounting: integrated standing seam clamp (no penetrations on standing seam) or ballasted on flat-roof sections. Result: new compliant roof + solar PV in a single construction programme.
Combined business case: making the numbers work
Re-roof costs: £15-30/sqm profiled steel; asbestos removal £10-20/sqm additional. Typical 5,000 sqm warehouse: re-roof £75,000-£150,000 + asbestos removal £50,000-£100,000 = £125,000-£250,000. Solar PV (500 kW on 5,000 sqm): £350,000-£400,000. Combined: £475,000-£650,000. Combined payback: 6-8yr. Standalone PV: 4.5-5.5yr. Combined makes economic sense when: (1) re-roof is a maintenance obligation regardless; (2) solar revenue offsets re-roof cost; (3) AIA applies to full combined project. Combined projects deliver 6-8yr payback vs re-roof-only at 10+ years with no revenue.
Tax treatment and CDM obligations
Capital allowances: solar PV (panels, inverters, mounting, electrical) — 100% AIA. Re-roofing (profiled steel, insulation) — generally qualifies as integral feature expenditure for AIA. Asbestos removal — deductible as revenue expenditure (environmental remediation) in most cases. Confirm with your tax advisor. CDM Regulations 2015: Principal Designer required (design phase); Principal Contractor required (construction phase); Construction Phase Plan required. Asbestos removal: HSE-licensed contractor mandatory under Regulation 8.
Common questions
Can solar PV be installed on an asbestos cement roof?
No. Asbestos cement roofing cannot receive solar PV — neither structurally nor from a health and safety perspective. AC disturbance risks asbestos fibre release. No UK insurer or HSE guidance permits PV on AC roofing. Combined re-roof (AC removal + profiled steel) + PV is the only viable path.
Does AIA apply to re-roofing costs in a combined project?
In most cases yes — thermal insulation on industrial buildings qualifies as integral feature expenditure for AIA. Your tax advisor should confirm the specific treatment. Asbestos removal is typically deductible as revenue expenditure. Confirm before project approval.