TryBuildCalcTerrace Waterproofing Calculator Liquid/PU membrane area estimator for terraces
Calculate waterproofing treatment area, material quantity, and cost for roofs, bathrooms, and basements.
🕒 Last updated: July 8, 2026
Inputs
Area Type
Roof / Terrace Dimensions
ℹ️Vertical upstand height where the roof coating turns up the parapet wall, commonly 150-300mm minimum.
Treatment Material
ℹ️Two coats, applied perpendicular to each other, is the common default.
ℹ️Liquid/PU membranes typically cover 1.0-1.5 kg/m² per coat — confirm against the product data sheet.
Wastage
Primer
Cost
This roof / terrace waterproofing job covers approximately 139.50 m² (1,502 sq ft) of treatment area — you'll need about 368.3 kg of material (material quantity includes 10% wastage).
Area Type
Roof / Terrace
Liquid / PU Membrane
Treatment Area
139.50 m²
1,502 sq ft
Wastage Allowance
10%
Extra material for corners, joints & off-cuts
Material Required
368.3 kg
2 coats at 1.2 kg/m² each, incl. wastage
Roof / Terrace Breakdown
Roof Area: 108.00 m² (1,163 sq ft)
Parapet Upstand Area: 31.50 m² (339 sq ft)
Wastage Impact on Material
Material Before Wastage: 334.8 kg
Extra Material From Wastage: 33.5 kg
Wastage sizes how much material to buy for detailing, joints, and off-cuts — the treated area itself (Treatment Area above) doesn't change.
Assumptions Used
Coverage rate: 1.2 kg/m² per coat | Coats: 2 | Wastage: 10%
Bill of Materials
Main material: 368.3 kg + recommended tools
+−
Bill of Materials
Main material: 368.3 kg + recommended tools
Computed items reflect your entered dimensions and material choice; consumables below are general recommendations — actual needs vary by product and site.
For Your Job
Liquid / PU Membrane
368.3 kg
2 coats × 1.2 kg/m²
General Tools & Consumables
Chemical-resistant gloves
Masking tape / polythene sheeting
Corner fillet / coving compound
Mixing bucket/drum & stirrer
Paint roller & brush set
Reinforcing fabric / mesh tape
Flood-test damming material (sandbags or timber battens)
Primer
Approximate results for planning only. Verify with a professional.
Choosing between cementitious, liquid/PU, and sheet membrane? Waterproofing Methods Guide →
Comparing this against a below-slab damp proof membrane? Damp Proof Membrane (DPM) Guide →
Roof / Terrace Waterproofing (Plan View)
Looking for the verification checklist, reference tables, or tips and mistakes?See the complete Waterproofing Calculator.
Terrace liquid membrane estimate
This page is pre-filled for a 12 m x 9 m terrace with a taller 0.75 m parapet upstand, using liquid/PU membrane at a 1.2 kg/m² coverage rate — treatment area comes to 139.5 m² (108 m² flat terrace plus 31.5 m² of parapet), needing about 368.28 kg of membrane material at 2 coats and 10% wastage.
Liquid/PU membranes cost more per kilogram than cementitious coating but bridge hairline cracks from thermal movement, which is why they're a common upgrade for terraces exposed to direct sun and temperature swings.
- Terrace: 12 m x 9 m.
- Parapet: 0.75 m.
- Material: liquid/PU membrane.
How Is Waterproofing Calculated?
Every mode follows the same overall sequence — calculate the treatment area for the chosen scenario, add wastage, then convert to material quantity (coating weight or membrane rolls), optional primer, and cost — but the area formula and material-quantity method differ by mode and material type.
Step 1 — Treatment Area (by Area Type)
Roof/Terrace = (Length × Width) + optional Parapet (Perimeter × Parapet Height)
Bathroom/Wet Area = (Floor Length × Width) + (Wall Perimeter × Wall Band Height) + optional Shower Wall (Width × (Height − Wall Band Height))
Basement/Retaining Wall = Wall Length × Wall Height
Multiple Sections = Sum of every section's area above, combined into one total
Roof and bathroom areas combine a horizontal face with an optional vertical upstand or wall band; basement waterproofing is calculated as a purely vertical external wall face. Switching on Multiple Sections lets you add several same-type areas (e.g. three bathrooms, or a stepped roof) in one run — each keeps its own dimensions and parapet/shower-wall choice, and the calculator adds every section's area together automatically.
Step 2 — Convert Area to Square Feet
Area (sq ft) = Area (m²) × 10.7639
Every area figure in this calculator — treatment area, material sizing area, and each mode's sub-areas — is shown in both units side by side, using the standard 1 m² = 10.7639 sq ft conversion factor.
Step 3 — Add Wastage
Material Sizing Area (m²) = Base Treatment Area × (1 + Wastage % ÷ 100)
Wastage is applied to size how much material to buy, not to the physical area — the actual treated area is always the Base Treatment Area from Step 1. This inflated figure only feeds into Step 4's material-quantity calculation, covering material used at detailing points (corners, joints, upstands) beyond the flat-area coverage rate, and off-cuts at sheet membrane joints.
Step 4 — Material Quantity (Coating vs Sheet)
Coating/Membrane: Material (kg) = Material Sizing Area × Coverage Rate per Coat × Number of Coats
Sheet: Effective Roll Coverage = (Roll Length × Roll Width) × (1 − Overlap % ÷ 100)
Sheet: Rolls Needed = ROUND UP(Material Sizing Area ÷ Effective Roll Coverage)
Cementitious and liquid/PU membrane systems are estimated by weight based on coverage rate and coat count; bituminous sheet membrane is estimated by roll count, with overlap reducing each roll's usable coverage.
Step 5 — Primer (Optional)
Primer Required (kg) = Material Sizing Area × Primer Coverage Rate
Primer Cost = Primer Required (kg) × Primer Rate per kg
Primer is modelled as a single, separate coat over the same material sizing area — at its own (typically lower) coverage rate — independent of the main coating or sheet method, since many liquid/PU membrane and sheet membrane systems specify a primer coat before the main material.
Step 6 — Calculate Cost (Optional)
Coating/Membrane: Material Cost = Material (kg) × Rate per kg
Sheet: Material Cost = Rolls Needed × Price per Roll
Labour Cost (rate per m²) = Material Sizing Area (m²) × Labour Rate per m²
Labour Cost (rate per sq ft) = Material Sizing Area (sq ft) × Labour Rate per sq ft
Total Cost = Material Cost + Primer Cost + Labour Cost
Labour can be priced per square metre or per square foot — the sq ft option matches the common Indian labour-rate convention — and either way the calculator converts it to an equivalent per-m² rate before computing labour cost.
Real-World Waterproofing Calculation Example
This example uses the active calculator mode, material type, and inputs above and follows the same steps from the formula section.
Input Values Used
| Input | Value | Why it is used |
|---|---|---|
| Area type | roof | Determines the treatment-area geometry used |
| Material type | membrane | Determines coating-weight vs sheet-roll calculation method |
| Wastage | 10% | Adds allowance before material quantity is calculated |
Step 1 — Treatment Area
| Calculation | Formula / Substitution | Result |
|---|---|---|
| Roof area | 12.00 × 9.00 | 108.00 m² (1,163 sq ft) |
| Parapet upstand area | Perimeter × parapet height | 31.50 m² (339 sq ft) |
| Base treatment area | Sum of the above | 139.50 m² (1,502 sq ft) |
Step 2 — Convert Area to Square Feet
| Calculation | Formula / Substitution | Result |
|---|---|---|
| Base treatment area in sq ft | 139.50 × 10.7639 | 1,502 sq ft |
Step 3 — Wastage
This step only sizes how much material to buy — the treated area stays the Base Treatment Area from Step 1.
| Calculation | Formula / Substitution | Result |
|---|---|---|
| Extra material-sizing area from wastage | 139.50 × (10 ÷ 100) | 13.95 m² (150 sq ft) |
| Material sizing area (incl. wastage) | 139.50 + 13.95 | 153.45 m² (1,652 sq ft) |
Step 4 — Material Quantity
| Calculation | Formula / Substitution | Result |
|---|---|---|
| Material per coat | 153.45 × 1.2 kg/m² | 184.1 kg |
| Total material (2 coats) | 184.1 × 2 | 368.3 kg |
Therefore, for this roof waterproofing job you have 139.50 m² (1,502 sq ft) of treated area — about 368.3 kg of material.
This page keeps things focused on the calculation above. For the full construction guide — verification checklist, reference tables, usage steps, tips, common mistakes, and limitations.See the complete Waterproofing Calculator.
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Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.