Turn an area in square feet and an illustrative per-sq-ft range into a low and high total, with one-off costs such as scaffolding or debris removal added on top.
Use this estimator to check whether a contractor's quotation is in a reasonable range for the area and system you have in mind. Pick a system to load an illustrative per-sq-ft range, enter the area you measured, and add the one-off costs that are charged as a lump sum rather than per sq ft, such as scaffolding or a rope-access setup, removal of old layers and debris, crack and joint repairs, or transport to an upper floor.
Formula: low total = area × low rate + one-off costs; high total = area × high rate + one-off costs. The result is before GST. For a works contract (supply and apply together) GST is generally 18% on the contract value; see GST on roofing, cladding and painting work.
Worked example (illustrative): a 1,000 sq ft terrace with a PU liquid membrane at ₹70–150 per sq ft and ₹15,000 for breaking out loose screed and debris removal. Low: 1,000 × 70 + 15,000 = ₹85,000. High: 1,000 × 150 + 15,000 = ₹1,65,000. With 18% GST the range becomes about ₹1,00,300 to ₹1,94,700.
Limits: the preset ranges are round, made-up figures chosen to show how pricing works. They are not market data and not prices from any contractor or brand. Real rates vary by city, season, height, access, product grade and the condition of the surface. Measure the area including parapet upturns and laps (see the terrace waterproofing worked example), and always ask for an itemised written quotation.
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