Measuring waterproofing for RA bills

Unit of measurement

Waterproofing of terraces and wet areas is measured in sqm. Waterproofing is measured as the area treated, including upturns on parapets and walls to the height the specification asks for.

The BOQ item description decides the unit and what the rate includes. Where the BOQ and this guide differ, the BOQ and the contract's mode of measurement win.

What is measured

• Plan area of the terrace or wet area treated.
• Upturns on parapets, walls and around pipes, as perimeter times upturn height.
• Treatment type (membrane, coating, brick bat coba), where the BOQ prices them separately.
• Protective screed or tiles over the treatment under their own items.

Standard deductions

• Openings, machine rooms and shafts not treated are deducted, as per the contract's mode of measurement and the relevant part of IS 1200.
• Overlaps of membrane are part of the rate and not measured.
• Small pipe penetrations are commonly not deducted.

Worked example

Ward office building, membrane waterproofing of the main terrace, with a 300 mm upturn on the parapet. B is the breadth or upturn height.

Row by row: Terrace, plan area, 1 x 18.5 x 12.4 = 229.40; Upturn on parapet, perimeter, 1 x 61.8 x 0.3 = 18.54; Less lift machine room, 1 x 3 x 2.5 = 7.50.

Total: 229.40 plus 18.54 minus 7.50 = 240.44 sqm. Deductions are entered with negative nos, so they reduce the total in the same column.

Common disputes

• Upturn height is claimed higher than the specification.
• Membrane overlaps are added to the area.
• The machine room floor, not treated, is left in the plan area.

Recording it in Tatha Vastu

Record the terrace and upturns as rows of one entry, with photos of each layer before it is covered. Photos taken before covering are the only evidence once the screed is laid.

Approved entries are locked, and a correction becomes a new version with its reason. See the measurement book, or use the measurement sheet template if you still keep the register in Excel.