STP ShaliDrainCell 30
A 30 mm high-impact polypropylene drainage cell that carries water away from roof gardens, podium decks and planters while protecting the waterproofing below.
What is it?
A 30 mm thick moulded panel of 100% high-impact polypropylene that creates an open drainage void beneath landscaped soil on roofs, podiums and planters.
Where is it used?
Roof gardens, terrace and podium landscaping, and below-ground planter boxes where planted soil sits over a waterproofed slab.
Why use it?
It moves excess irrigation and rainwater off the membrane quickly, preventing waterlogging of soil and hydrostatic pressure on the waterproofing beneath.
How is it applied?
Laid loose over the finished waterproofing membrane, panels interlocked to shape, then covered with a geotextile filter fabric before soil is placed.
About STP ShaliDrainCell 30
STP ShaliDrainCell 30 is the drainage layer in a roof-garden or podium-landscape build-up. It is a moulded cellular panel made from 100% high-impact polypropylene, 30 mm thick, that sits directly on the waterproofing membrane. The three-dimensional cell structure holds an open air gap so that water percolating down through the planting soil has a continuous, low-resistance path to travel sideways and reach the outlets, instead of pooling on the slab. For Delhi-NCR and pan-India projects where terrace gardens, green roofs and podium plazas are increasingly specified, it solves the single biggest cause of green-roof failure: water that has nowhere to go.
Space Arc Engineering supplies ShaliDrainCell 30 as an authorised STP distributor and installs it as part of a complete waterproofing-plus-drainage system. On its own a drainage cell is only half the answer; it has to sit on sound waterproofing and be topped with the right filter fabric so that soil fines do not wash into and choke the void. Because we handle the membrane, the cell and the geotextile as one package, the layers are compatible and correctly sequenced rather than sourced piecemeal from three different vendors and hoped to work together.
The technical insight
The mechanism is simple physics done well. Planted soil over a flat slab behaves like a sponge sitting in a tray: without drainage, water fills the soil from the bottom up, roots suffocate, and a standing head of water presses down on the waterproofing and hunts for the smallest defect. ShaliDrainCell 30 breaks that cycle by introducing a 30 mm rigid air gap between soil and slab. Water that reaches the base of the soil drops into the cell void and flows laterally under gravity to the roof drains, so the soil profile drains freely and the membrane never sees a sustained water column. The high-impact polypropylene gives the cell the crush resistance to keep that void open under the dead load of saturated soil, paving or foot traffic above, and polypropylene’s chemical inertness means it does not rot, corrode or react with soil, fertiliser or root activity over the life of the landscape. The geotextile placed on top is not optional trim: it is the filter that lets water pass while holding back the fine soil particles that would otherwise silt up the void and defeat the whole system.
Where it is used
- Intensive and extensive green-roof and terrace-garden build-ups over RCC slabs
- Podium-deck and plaza landscaping above basements and car parks
- Roof gardens where irrigation and monsoon runoff must be drained clear of the membrane
- Below-ground and raised planter boxes needing a free-draining base
- Landscaped courtyards and sunken gardens over occupied space
- Sub-soil drainage beneath lawns and planted areas on structural slabs
Key advantages
- 30 mm open void gives soil water a fast lateral escape path to the drains
- High-impact polypropylene resists crushing under saturated soil and imposed loads
- Chemically inert – does not rot, corrode or react with soil, roots or fertiliser
- Lightweight panels add little dead load compared with a gravel drainage bed
- Cuts and interlocks easily to suit irregular roof shapes and around penetrations
- Protects the waterproofing membrane from root activity and standing water
- Speeds up installation versus laying and levelling loose aggregate drainage
Limitations & considerations
- Only performs as the drainage layer – it does not waterproof; a sound membrane must already be in place beneath it
- Must be covered with a geotextile filter fabric, or soil fines will migrate in and clog the void
- Falls and outlet positions on the slab still govern drainage; the cell moves water sideways but cannot pump it uphill
- Not a structural or load-spreading paving layer on its own – heavy point loads need proper build-up above
- Publicly published mechanical and flow figures are limited, so load-critical designs should be confirmed against STP’s current technical data sheet for the project
Selection & best practice
Install ShaliDrainCell 30 only after the waterproofing membrane has been laid, cured and, where required, flood-tested and signed off – the cell is the layer above the waterproofing, never a substitute for it. Lay the panels loose directly on the membrane and interlock them, cutting to fit around drains, upstands and penetrations; keep the cutting neat so the void stays continuous to the outlets. Confirm the slab has adequate falls toward the roof drains before covering anything, because the cell conveys water laterally but relies on that fall to move it to the outlets. Always cover the full cell area with a non-woven geotextile filter fabric, lapped at joints, before placing growing medium – this is what keeps soil out of the drainage void. Finally, protect exposed membrane and installed cells from prolonged sun and site traffic until the soil layer goes on.
Specifications
| Product | STP ShaliDrainCell 30 |
| Manufacturer | STP Limited |
| Type | Moulded cellular drainage panel |
| Material | 100% high-impact polypropylene |
| Thickness / cell height | 30 mm |
| Function | Sub-soil drainage layer for roof gardens and podium landscaping |
| Position in build-up | Over the waterproofing membrane, beneath the geotextile filter and soil |
| Required overlay | Non-woven geotextile filter fabric |
Industry use cases
Commercial podium landscaping
Green plazas and gardens over basement car parks, where drainage must keep water off the deck membrane and clear of the structure below.
Residential terrace gardens
Roof and terrace gardens on apartments and villas that need free-draining soil without waterlogging or leaks into rooms beneath.
Hospitality and institutional roofs
Hotel, campus and hospital green roofs where extensive planting sits over occupied space and reliable drainage is critical.
Landscape and horticulture contractors
Planter boxes, raised beds and sunken gardens needing a lightweight, quick-to-lay drainage base over waterproofed structure.
Frequently asked questions
Is ShaliDrainCell 30 made of HDPE or polypropylene?
Does ShaliDrainCell 30 waterproof the roof by itself?
Why do I need a geotextile fabric over it?
What thickness or cell height does it come in?
Can it take the weight of soil, paving and foot traffic on top?
Can Space Arc supply and install it as a complete system?
How we position STP ShaliDrainCell 30
ShaliDrainCell 30 is the drainage layer, not the waterproofing, so it is almost always specified alongside a membrane and filter fabric. Within STP’s own ShaliDrain range, choose a different ShaliDrainCell height when the build-up calls for a deeper or shallower drainage void than 30 mm, and always pair it with a non-woven geotextile filter. On the waterproofing side beneath it, the natural partner from our Fosroc range is Nitoproof 600, the pitch-modified polyurethane membrane whose own applications list planter boxes and inverted roofs – exactly the concealed, buried situations a roof-garden drainage cell sits over. Where the specification favours a torch-applied bituminous system for a podium or terrace, Fosroc Proofex Torchseal is the alternative membrane beneath the same drainage build-up. For projects standardising on a single manufacturer, STP’s own ShaliTex geotextiles and waterproofing membranes complete the assembly.
Fosroc Nitoproof 600 — Choose this when you want a proven Fosroc polyurethane waterproofing membrane beneath the roof garden, since ShaliDrainCell 30 is only the drainage layer and needs a sound membrane under it – Nitoproof 600’s own applications include planter boxes and inverted roofs.
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