Expect to pay on average between £140 – £190 per m² for a flat roof depending on the material. Felt roofs are cheapest at around £140 per m², whereas fibreglass is usually the highest at £188 per m².
Cost per m²
To get the total flat roof cost, you’ll need to add the base cost (£99/m²) plus the type of finishing, which are given in the second table.
Base Costs
These are the costs minus the roof finishing layer.
| Item | Labour Cost per m² | Material Cost per m² | Total Cost per m² |
|---|---|---|---|
| Ceiling Joists – 150mm x 75mm | £19 | £31 | £50 |
| Plywood – 18mm thick | £14 | £16 | £30 |
| Vapour Control Layer | £1 | £2 | £3 |
| Slab Insulation – 120mm thick Celotex | £7 | £22 | £2 |
| Total | £41 | £69 | £110 |
Total Costs Including Roof Finishing Layer
These include different types of finishing layers. The total cost is the base cost + the finishing material cost.
| Item | Cost per m² | Total Cost (Base + Roof Finishing) / m² |
|---|---|---|
| Fibreglass / GRP | £78 | £188 |
| PVC | £55 | £165 |
| Bitumen | £52 | £162 |
| EPDM Rubber | £65 | £175 |
| Roofing Felt | £30 | £140 |
Additional Items
These are additional items and may not be needed. Speak to your roofing contractor.
| Item | Cost |
|---|---|
| PVC Gutters | £20 / m |
| Aluminium Gutters | £36 / m |
| Flashings | £39 / m |
| Aluminium Downpipes | £46 / m |
| Flashings | £22 – £38 / m |
Factors That Affect Cost
Specification
Jobs can vary considerably. For example, there may be more additional items needed such as guttering and flashing. Other items that can vary the cost include multiple or complicated trims, ventilation and insulation.
Size
Larger roofs will cost less per m² than smaller ones. Generally over a 100m² would see a 5% reduction in cost.
Accessibility
Costs increase the higher the flat roof is, which is dependant on the storey it’s at. Flat roofs on a 3 storey building will be higher than one a few feet high for example. This is because scaffolding may be necessary at larger heights as well as less accessibility.
Tradesman’s Markup
Every business has different overheads and expensive, and businesses will factor these into their price different. Skilled tradesmen are more likely to be busy and can charge higher prices.
Although prices above give a good indication of what to pay, it’s not a good idea to always go for the cheapest. Standards can drop considerably if you go for the cheapest price.
Location
Areas in the south of England and London will be higher than in other parts of the country. The prices quoted in the table above apply for the South East or Outer London area. The adjustments below can be used to calculate costs in your area.
| Region | % Adjustment |
|---|---|
| South East (Southampton, Oxford, Kent, Outer London) | 0 |
| Inner London | +4% |
| South West (Bristol, Exeter) | -4% |
| West Midlands (Birmingham) | -10% |
| East Midlands (Northampton, Nottingham, Leicester) | -10% |
| East Anglia (Cambridge, Norwich, Ipswich) | -5% |
| North West (Liverpool, Manchester) | -12% |
| Yorkshire and Humberside (Leeds, Sheffield) | -11% |
| North East (Newcastle, Sunderland) | -10% |
| Scotland (Edinburgh, Glasgow) | -6% |
| Wales (Cardiff, Swansea) | -9% |
| Northern Ireland (Belfas |