Landscaped terraces, podium gardens and balcony planters make buildings greener and more attractive. They also bring water, soil and roots into places that sit directly above living spaces. Without the right drainage details, they become a major source of leaks and staining.
Planter drainage basics
- Every planter needs a drainage outlet at its lowest point.
- Use a drainage layer (a drainage board or gravel) above the waterproofing.
- Add a filter fabric so soil does not wash into the drainage layer and outlet.
- Use a root barrier where planting could damage the membrane.
Use the right drain
Planter drains have extension pieces and perforated covers so they collect water from the drainage layer while keeping soil out. An inspection access point at the surface makes maintenance much easier.
Balcony drainage
Balconies need a small but reliable outlet: a balcony drain with a membrane clamping flange, or a scupper through the parapet. Make sure the floor falls towards the outlet, and that door thresholds sit above the balcony water level.
Overflow protection
If an outlet blocks, water should have a safe secondary route that does not flow into the building, such as an overflow scupper set slightly higher than the main outlet.
Maintenance
- Clear leaves and soil from outlets regularly.
- Check irrigation settings, since over-watering is a common cause of saturated planters.
- Inspect after storms.
Which drain?
| Location | Drain |
|---|---|
| Planter | Planter drain with mesh dome (cast iron or PVC, 1.5″–4″) |
| Balcony | Balcony drain with dome or flat grate |
| Parapet wall | Scupper roof drain |
| Terrace on pedestals | Flat roof drain under a removable paver |
Layer by layer
- Structural slab laid to falls.
- Waterproofing membrane, bonded to the drain flange.
- Protection layer and root barrier.
- Drainage board or gravel.
- Filter fabric.
- Soil and planting, with the planter drain reaching up to an inspection point.
GRP planters on podiums
Where planters sit on podiums and roofs, GRP planter boxes are much lighter than concrete and can be made to size.
Frequently asked questions
Why does my planter leak into the flat below?
Usually a blocked outlet, a missing filter layer or a membrane not bonded to the drain flange. Water then builds up and finds a way through.
How often should planter drains be cleaned?
At least twice a year and after storms, more often under trees.
Mesh dome or flat grate?
A mesh dome for planters, where soil and roots must be kept out; a flat grate for balconies and terraces people walk on.
Products for terraces
We supply planter drains, balcony drains and roof outlets. See our drainage accessories.
Related: Landscape Drainage Channels · GRP Planter Boxes
Related products: planter and balcony drains · roof drains · scupper and parapet drains
Related products: Planter Drain with Mesh Dome