Flat roof renewal (EPDM / GRP / felt): calculator for UK builders
Answer the measurements this calculation needs and JobBosh works out the materials with wastage and pack rounding, the labour hours by role, the plant, the waste and the site needs - then prices them from your own figures, a supplier's quotation or a dated price you record. Free, no account needed to start.
What it works out
- Material: EPDM membrane + adhesive + trims; 18 mm OSB3 decking (2440 x 1220); Edge trims, drip, outlets, sealant
- Labour: Strip old covering and deck; Lay new deck; Lay covering and trims
- Waste: Old felt, deck, insulation
The questions it asks
| Question | Unit / choices | Required? | Help |
|---|---|---|---|
| Flat roof area | m2 | required | |
| System | one of: epdm, grp, torch on felt | optional - default epdm (labelled assumed) | |
| Renew the decking? | yes / no | optional - default yes (labelled assumed) | |
| Add insulation (warm roof)? | yes / no | optional - default no (labelled assumed) |
The norms behind it, with their sources
Coverage, productivity and wastage defaults you can edit; each carries where it comes from and is shown as assumed until your own benchmark replaces it.
| Norm | Value | Source | Tier |
|---|---|---|---|
| Strip old covering per m2 | 0.2 hr/m2 | trade practice | assumed |
| Lay new OSB deck per m2 | 0.3 hr/m2 | trade practice | assumed |
| Lay covering incl. trims per m2 | 0.5 hr/m2 | trade practice | assumed |
A worked example
Answers used: Flat roof area 20 m2; System epdm; Renew the decking? yes; Add insulation (warm roof)? no. These are the recipe's own quantities for those answers - the prices are yours, the supplier's or a quotation's, never a figure typed on a web page.
| Kind | Line | Quantity | How it is worked out |
|---|---|---|---|
| material | EPDM membrane + adhesive + trims | 22 m2 22 x m2 - per m2 (kits by area) | 20 m2 +10 % |
| material | 18 mm OSB3 decking (2440 x 1220) | 22 m2 8 x sheet - 2.98 m2 sheets | 20 m2 |
| material | Edge trims, drip, outlets, sealant | 1 item | one allowance |
| labour | Strip old covering and deck | 4 hr | 20 m2 x 0.2 h/m2 |
| labour | Lay new deck | 6 hr | 20 m2 x 0.3 h/m2 |
| labour | Lay covering and trims | 10 hr | 20 m2 x 0.5 h/m2 |
| waste | Old felt, deck, insulation | 1 m3 | 20 m2 x 0.05 m3/m2 |
Labour on this example: about 20 hours across the roles; at your rates it becomes money.
Site questions this work raises: Access equipment and temporary works, Waste, Parking and traffic.
Specialists or hire it may need, drafted as enquiries from the job's facts: Waste removal (man and van / clearance).
Then what
Price the lines from your crew rates and your material prices (each with its source and date), answer the site questions (parking, skip, welfare, power, water, protection), let JobBosh draft the supplier enquiries you approve, and issue a branded quotation your customer accepts on a secure link. Guest work is kept for 14 days; a free account keeps it for good.