Green Roof Drainage & Water Reservoir Board – HDPE Cuspated Core, 12mm & 20mm, 4 Roof Sizes

Every green roof kit bundles a drainage layer into the price, but that standard-depth layer isn't always the right one — a custom build-up, a roof that needs extra water attenuation for SUDS compliance, or a kit whose stock drainage layer needs topping up after a repair all call for this board on its own. It sits between the waterproofing and the growing medium, doing three jobs at once: draining surplus water away so roots don't sit waterlogged, holding a reservoir of water back for the plants to draw on in dry spells, and protecting the membrane beneath from root penetration and mechanical damage. HDPE cuspated core drainage board with integral filter fleece Two depths: 12mm (1.5 L/m² water attenuation) and 20mm (5.5 L/m² water attenuation) Supplied by roof area, matching the size bands of our complete sedum kit Sits directly above the waterproofing membrane, below the growing medium and sedum blanket Specification Depth Water attenuation Core 12mm 1.5 L/m² HDPE cuspated, fleece-faced 20mm 5.5 L/m² HDPE cuspated, dual-fleece faced Sizes 6m², 12m², 20m², 30m² Position in build-up Above waterproofing membrane, below growing medium Function Drainage, water attenuation, root protection, membrane protection Frequently asked questions Do I need this if I'm buying your complete sedum kit? No — our Sedum Green Roof System already includes a drainage/water reservoir layer in the price. Buy this separately if you're building a custom system from individual layers, need to top up or repair an existing green roof's drainage layer, or want the heavier 20mm depth in place of a kit's standard layer. Which depth should I choose? 12mm suits lightweight or retrofit systems where roof load is tightly constrained. 20mm holds more than three times the water reserve and is the better choice where you want the sedum to cope better through dry spells, provided the extra weight and depth are accounted for in your structural check. Does this replace a root barrier? Not on its own — check whether your waterproofing membrane is already root-resistant (EPDM rubber generally is) before assuming this board alone stops root penetration; on non-root-resistant membranes, fit a dedicated root barrier beneath it. Which way up does it go? Fleece face up, so the growing medium doesn't wash into the drainage channels beneath. Cuspated (dimpled) face down, against the waterproofing. Will this affect my roof's structural loading? Yes — always add the saturated weight of this board's water attenuation to the rest of your green roof build-up (substrate, planting, standing water) when checking structural capacity, the same as for a complete kit. Building a green roof from individual layers? Waterproof first with our 1.2mm EPDM rubber membrane, lay this drainage board over it, then finish with the growing medium and sedum blanket from our complete Sedum Green Roof System if you'd rather not source the top layers separately.