Using a terrace for planting is becoming increasingly common in urban India, where open land is limited. But a terrace garden must be prepared correctly to prevent leakage and long-term structural damage. Professionals follow a clear, layered system to protect the building while creating healthy conditions for plants. Below is an objective breakdown of each layer and its role.
Waterproofing layer: The first line of protection
The process begins with applying a high-quality waterproof paint or membrane across the entire terrace. This layer prevents moisture from entering the slab and walls below. It must be continuous and free of cracks, with two to three coats applied and allowed to dry fully. The waterproof coating should also extend slightly up the parapet walls to seal all possible entry points for water.
Root barrier sheet: Preventing structural damage
Once waterproofing is complete, a root barrier sheet is installed. This protective membrane prevents plant roots from penetrating or damaging the waterproof layer. Roots can follow moisture and enter even tiny cracks over time. The barrier blocks this movement, ensuring long-term protection. It should be laid smoothly, with overlaps sealed so that no soil or moisture can bypass it.
Drain cell layer: Allowing water to flow out
Next comes the drainage system. Drain cells — typically 30 to 50 mm thick — are placed across the terrace to create a cavity under the soil. This layer ensures excess water flows freely towards the outlets instead of accumulating under the soil. Proper drainage reduces pressure on the slab and prevents seepage. The air pockets created by drain cells also help maintain a healthier root environment.
Geotextile fabric: Keeping soil and water separate
Above the drain cells, a geotextile fabric (geofabric) is laid. This acts as a filter, allowing water to pass through while keeping soil particles above. Without this layer, soil would clog the drain cells and block water movement. The geofabric ensures long-term drainage efficiency and keeps the soil layer stable. It should cover the entire area with sufficient overlaps.
Lightweight soil mix: Safe medium for plant growth
The final layer is a lightweight soil mix suited for terrace use. Regular heavy garden soil increases the load on the slab and should be avoided. Instead, a mix of red soil, compost, cocopeat, and aerating components like pumice or perlite is used. This blend supports healthy plant growth while keeping the overall weight manageable. Soil is unloaded onto the geofabric and spread evenly to maintain uniform load distribution.
By building these layers — waterproofing, root barrier, drain cells, geotextile fabric, and lightweight soil — a terrace becomes safe, durable, and ready for planting. These steps ensure long-term protection from leakage while creating a well-functioning environment for terrace gardens.