Roof Garden & Green Roof Waterproofing
Root Barrier, Drainage & Build-Up

Roof garden, planter or green roof?

Three things get called a roof garden in Malaysia. Pots and loose planters on a terrace are the simplest: the roof membrane stays exposed and the pots sit on feet. Built-in planter boxes are waterproofed as their own troughs; our planter box waterproofing guide covers them. A true green roof spreads a growing medium across the roof itself, so the whole slab becomes the planter. This page is about the last one, and about large rooftop planting beds that behave like it.

Wikipedia’s green roof article describes a green roof as vegetation and a growing medium planted over a waterproofing membrane, often with a root barrier, drainage and irrigation added.

Extensive and intensive green roofs

Green roofs are usually split into two kinds, and the difference drives weight, cost and upkeep.

The depths above are the definitions in the Wikipedia article. In practice a Malaysian roof garden with lawn, shrubs and a seating area is intensive, and that is the kind that needs the most careful structural check.

The build-up, layer by layer

A roof garden that stays dry underneath is a stack of layers, each protecting the one below. Our planter box guide sets out the same principle at trough scale; on a roof it runs across the whole slab.

1. Structural slab, repaired and laid to falls so water runs to the outlets.
2. Waterproofing membrane, carried up the walls and kerbs above soil level and sealed into every outlet.
3. Root barrier, a root-resistant sheet or a membrane rated to resist roots.
4. Protection layer, board or mat that shields the membrane from tools, stones and root pressure.
5. Drainage layer, usually drainage cell panels that leave a free-draining void.
6. Filter fabric (geotextile), which keeps soil fines out of the drainage layer.
7. Growing medium and plants on top.

Our rooftop terrace guide makes the same point for terraces: for full roof gardens with lawns and soil beds, a purpose-made root-barrier membrane and a drainage-cell layer under the soil are essential, because repairing a membrane under tonnes of landscaping is a project nobody enjoys pricing.

Why an ordinary membrane is not enough

Roots hunt for water. A lap in a sheet membrane or a hairline crack in a coating holds a film of moisture, and roots find it, grow into it and split it open over time. The planter box guide names bamboo, ficus and most trees as notorious planter-killers and recommends a proper HDPE root barrier over the protection layer where aggressive species are planted. On a green roof the barrier runs across the whole planted area and up the upstands, with its joints sealed, not simply overlapped.

Drainage decides whether it lasts

Waterlogged soil on a roof is heavy, kills plants and keeps the membrane under constant water. Good drainage has several parts:

• Falls in the slab or screed so water runs to the outlets instead of ponding.
• A drainage cell layer that carries water sideways under the soil.
• Filter fabric that keeps soil out of that layer, so it does not clog.
• Outlets with inspection chambers, so they can be checked and cleared without digging.
• An overflow route in case an outlet blocks in a storm.

The planter guide prices drainage cell and geotextile as an add-on at RM8–RM15 per sq ft over a new membrane. It is the layer most often value-engineered out, and the one most often regretted.

Weight: check the slab first

Saturated soil, plants, paving and people add a great deal of weight to a roof that may have been designed only for maintenance access. Before a roof garden is planned, a structural engineer should confirm what the slab can carry, with the soil wet, not dry. Extensive roofs with shallow growing media are far lighter than a lawn and shrub garden, which is one reason many homes choose planters or pots instead of a full green roof.

Adding a garden to an existing roof

Planting over an old membrane is the most common mistake. If the existing waterproofing is already a decade old or has been patched, it will have to be replaced before soil goes on top, because it cannot be reached afterwards. The usual sequence is to strip the roof to the slab, repair it, install the new system with its root barrier and drainage, and flood-test it before the garden is built. Our flat roof waterproofing guide covers the membrane choices.

Choosing plants for a roof

• Prefer shallow-rooted shrubs, herbs, grasses and ground cover.
• Keep bamboo, ficus and trees in pots placed inside the bed rather than planted into it.
• Choose plants that cope with full sun, wind and dry spells on an exposed roof.
• Group thirsty plants together so irrigation can be zoned.

Irrigation and maintenance

A roof garden needs a routine. Clear leaves and soil from outlets before the monsoon, check that the overflow is open, pull out self-seeded trees before their roots get established, and look at the upstands where the membrane rises above the soil. Drip irrigation keeps water where plants need it and avoids flooding the drainage layer. If a stain appears on the ceiling below, get the source found before digging: our leak detection guide explains how.

Condos and strata rules

On a condo or apartment roof, the roof slab and its waterproofing are usually common property. A resident cannot build a garden on it without approval, and a management body planning a communal roof garden should treat it as a waterproofing project first. Our condo rooftop guide explains how JMBs plan roof waterproofing.

What it costs

These are figures published on ClickBina’s own guides (indicative Klang Valley). Landscaping, soil and plants are priced on top.

Roof size, access for materials, the state of the existing slab and whether a root barrier is a separate sheet or part of the membrane are the main things that move a quote.

How ClickBina can help

A roof garden touches the slab, the waterproofing, the drainage, the plumbing for irrigation and the ceiling below. ClickBina handles whole-house refurbishment and coordinates those trades on one job. WhatsApp us your job details for a quote: the roof area, whether it is a new build or an existing roof, and the kind of garden you want. We reply within the hour, the price we agree is a flat price with no hidden charges, and a site visit is RM150, waived if you go ahead.

Sources & methodology

• Wikipedia, Green roof — definition, and the extensive and intensive growing depths.
• ClickBina rooftop terrace and planter box waterproofing guides — the layered build-up, root barriers, drainage and prices.
• ClickBina flat roof, condo rooftop and leak detection guides — membrane choice, strata roofs and finding leaks.

Pricing note: prices are indicative Klang Valley figures quoted from ClickBina’s published guides. A roof garden is priced in writing after the roof and slab have been inspected.