A green roof or a deep planter fails from the bottom up. Water that cannot leave the assembly kills plants, saturates insulation and eventually finds the building interior. Drainage cells are the layer that prevents that story: dimpled HDPE sheets that hold soil up while letting water run free to the outlets. We mold drainage cells and ship them to US roofing distributors and landscape contractors, and here is the layer-by-layer version of the conversation.
Heights and what they are for
Cells run 20 mm for extensive green roofs and planters, 25 mm for intensive roofs and podium decks, 30 mm where retention volume and flow are the priority. Height is storage and flow: deeper cups hold more water in retention designs and move more water in drainage designs. Compressive strength matters more than most buyers realize, because a drained layer under saturated soil carries serious loads; our cells are specified for the dead loads of real assemblies, not just foot traffic.
The build-up, in order
- Structural deck with waterproofing membrane (the membrane is sacred; protect it).
- Root barrier where needed, per planting plan.
- Protection layer over the membrane.
- Drainage cell, cups down for retention, or cups up per the assembly drawing.
- Filter geotextile over the cell so fines never enter the cups.
- Growing medium and planting.
The geotextile step is where installs go wrong. A missing or folded-under filter lets soil migrate into the cups, and drainage capacity quietly disappears over a few seasons. Filtration is cheap; retrofit is not.
Indicative pricing
Drainage cells run roughly $1.20 to $2.20 per square foot FOB India depending on height, plus the geotextile layer at a few cents. Interlocking edges make installation fast, crews report several thousand square feet a day on straightforward decks. A 40-ft container carries a substantial square footage because sheets nest, keeping freight per square foot modest. Production is 3 to 4 weeks; ocean 4 to 6 weeks either coast.
Contractor and specifier questions
Cups up or cups down?
Follow the assembly drawing: cups down promotes free drainage toward outlets, cups up adds retention volume for the plants. It is a design decision, not a preference, and both are valid in different specs.
What about outlet and inspection chambers?
We supply companion outlet pieces and flush-access components; specify them with the cells so the drainage path is complete from cup to outlet, which is the whole point of the layer.
Heights, strengths and accessories are on the Drainage Cell page. Related drainage products: geonet composites and the HDPE pond liner guide.
