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Waterproofing Material Planner

Waterproofing area = flat area + perimeter × upstand height, plus waste. A 120 m² roof with 50 m of 150 mm upstands is 127.5 m², or 140 m² with 10%. Two coats of a liquid membrane at 1.0 kg/m² per coat need 281 kg (15 pails of 20 kg) and about 28 L of primer.

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Behind this panel: an example with the default sizes.

Inputs

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Area
m²
m
mm
System
%
Waterproofing with upstandArea 140.3 m²150 mmliquid membrane with upstandmyconstructioncalculator.comNot to scale
Diagram updates as you type.

Results

Check the working before you order.

Coating material
281kg
20 kg pails15
Area incl. upstands and waste140.3 m²
Primer28.1 L

Reinforce cracks, joints and corners with fabric as specified, and check the minimum dry film thickness.

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Working
  1. Area = (120.0 + 50.0 × 0.15) × 1.10 = 140.3 m²
  2. Material = area × 2 coats × 1.00 kg/m² = 281 kg
Results are estimates for planning and material ordering only. They are not a substitute for structural design or approval by a qualified engineer. Read the full disclaimer.
Formulas


Area          = flat area + perimeter × upstand, × (1 + waste)
Coatings      = area × coats × kg/m² per coat
Sheet rolls   = ⌈area ÷ ((roll width − side lap) × (roll length − end lap))⌉
Primer        = area ÷ coverage


Worked Example


120 m² roof, 50 m of 150 mm upstands, liquid membrane 2 coats × 1.0 kg/m², 10% waste:


    

  1. Area = (120 + 7.5) × 1.1 = 140.3 m²
    2. 

  2. Membrane = 140.3 × 2 × 1.0 = 281 kg → 15 pails
    3. 

  3. Primer at 5 m²/L = 28 L
    4. 



Sheet Membrane Cover per Roll






Roll
Laps (side / end)
Net cover






1 × 10 m
100 / 150 mm
8.87 m²




1 × 15 m
100 / 150 mm
13.37 m²




1 × 20 m
75 / 100 mm
18.41 m²






Frequently Asked Questions
How much liquid waterproofing do I need?
Area × coats × consumption per coat from the data sheet, often 0.75–1.5 kg/m² per coat for liquid membranes. Include upstands and add 5–10%.
How many membrane rolls for a roof?
Each roll covers (width − side lap) × (length − end lap). A 1 × 10 m roll with 100 mm side and 150 mm end laps covers about 8.9 m².
How high should waterproofing turn up the walls?
Commonly at least 150 mm above the finished surface, and higher at parapets and in showers. Follow the system's details.
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