A green roof anti-root membrane is the waterproofing layer that stays sound under soil, water and living roots. A planted roof keeps the membrane damp most of the time. Meanwhile, roots search for any weak point in it. So a normal roof build-up is not enough. This guide covers the membrane, the protection layer, the edge details and testing, and how Target approaches roof gardens.
Contents
- Why planted roofs are a special risk
- The anti-root SBS membrane
- Protection boards over the green roof anti-root membrane
- Upstands and flashings
- Site storage and handling
- Execution steps
- Common mistakes on planted roofs
- FAQ
- Conclusion
Why planted roofs are a special risk
A green roof differs from an exposed roof in three ways. First, the soil keeps the waterproofing wet for long periods. Second, roots grow towards moisture, so they reach laps and small defects. Third, any leak is hard to find and costly to reach under soil and planting.
For these reasons, the waterproofing must resist roots, rot and site damage, not just water. This is why a green roof anti-root membrane, rather than a standard roll, is the starting point of the build-up. In Egypt, roof gardens now appear on villas, hotels and commercial podiums, so the question comes up often.
The anti-root SBS membrane
HYPERFLEX-P20 Anti-Root, from Modern Waterproofing Company in Cairo, is an SBS-modified bitumen membrane. It is a form of modified bitumen roll roofing. Its reinforcement is a heavy composite polyester armoured with glass fibre filaments. In addition, a special chemical additive gives it rot-proof features.
The data sheet lists two uses: lining of flower boxes and waterproofing of green areas on roofs. It also names resistance to plant roots and to soil chemicals and salts “up to certain limits”.
Key values from the sheet (based on 4 mm):
- Cold flexibility −20 °C (EN 1109); heat resistance 100 °C (EN 1110).
- Tensile strength 1000 N/5 cm long, 750 N/5 cm wide (EN 12311-1).
- Static puncture 20 kg (EN 12730); dynamic puncture 1750 mm (EN 12691).
- Rolls 10 m × 1 m; standard thicknesses 3 and 4 mm.
Laying on sloped roofs
The sheet describes torch application, either loose-laid or fully bonded, depending on the system. On sloping roofs, laying starts at the lower edge. The rolls run across the slope, and each new roll laps over the one below it. In this way, water always flows over the laps, not into them.
Bitumode Alpha-P from the same maker also lists an anti-root type for green areas on roofs. Still, specify the anti-root grade by name, so the right rolls arrive on site.
Protection boards over the green roof anti-root membrane
Over time, soil, gravel and gardening tools can damage the membrane. Therefore, a protection layer goes on top before any drainage or soil.
Fox CARTOTECH G400 is a 3 mm polypropylene protection board from an Egyptian maker. Its sheet describes it as puncture-resistant and root-proof, and states that it does not rot or support bacterial growth. The technical table gives a puncture resistance of 1100 N (BS EN ISO 12236). Boards are 1 m × 2 m, at about 400 g/m².
In practice, installation is simple. First, the crew lightly torches the membrane in separate spots until it turns sticky, then presses the board on. The sheet recommends a 3–5 cm overlap between boards. The sheet also notes that the board is flexible enough for corners, protrusions, and rounded or uneven surfaces. That helps in planter boxes and soil-covered upstands.
| Layer | Product (data sheet) | Role | Key values |
|---|---|---|---|
| Primer | NIROL-W or NIROL-S | Bonding to concrete | Named on HYPERFLEX-P20 sheet |
| Waterproofing | HYPERFLEX-P20 Anti-Root | Root- and rot-resistant membrane | −20 °C; 1000/750 N/5 cm |
| Flashings | Impermax B 1K | Upstands and penetrations | > 400% elongation; CEN/TS 14416 |
| Protection | Fox CARTOTECH G400 | Puncture and root protection | 1100 N; 3 mm PP |
| Above | Drainage, filter, soil | Per landscape design | Outside these sheets |
Upstands and flashings
Roots and water both attack the edges first. So parapets, planter walls, drains and pipe penetrations need extra care.
The HYPERFLEX-P20 sheet asks for 5 × 5 cm sand-cement cant strips at horizontal-vertical corners. As a result, the membrane never folds into a sharp 90° angle.
For complex details, Impermax B 1K from Krypton Chemical offers a liquid option. It is a single-component PU-bitumen membrane “specially designed for flashing”. Its sheet lists root resistance to CEN/TS 14416:2014 and elongation above 400%. It is applied at about 1.5–2 kg/m² in one or two layers. However, the sheet lists it for unexposed surfaces, so the finished flashing should stay covered.
The substrate also matters. According to the sheet, it must be flat, clean and dry, with a pull-off strength of at least 1.4 N/mm². Moreover, air temperature must stay between 0 and 30 °C. High moisture can cause bubbles under the film.
Site storage and handling
Good details fail if the rolls arrive damaged. For this reason, the HYPERFLEX-P20 sheet asks for vertical storage in a covered, ventilated place, away from direct sun. It also warns that rolls must never fall or be thrown from the truck.
Likewise, protection boards need a clean stack away from site traffic. According to its sheet, Fox CARTOTECH absorbs no water and is not affected by mineral oils, acids, bases or salts found in soil.
Execution steps
At Target, a green roof waterproofing job follows this order:
- Check the slab slope and drains; correct with a sand-cement screed if needed.
- Form 5 × 5 cm cant strips at all upstands.
- Prime with NIROL-W or NIROL-S and let it dry.
- Torch-apply the green roof anti-root membrane with 10 cm side laps and 15 cm staggered end laps.
- Seal upstands and penetrations, using Impermax B 1K where details are complex.
- Flood-test the roof to the project specification before covering.
- Spot-torch Fox CARTOTECH boards with 3–5 cm overlaps.
- Hand over to the landscape team for drainage, filter and soil.
Coordinating with the landscape team
Much roof garden damage happens after the waterproofing is complete. For example, planting crews may drive stakes or irrigation pipes through the protection layer. So we agree on irrigation routes, drain positions and any fixings in advance. We also ask for no sharp tools near upstands. If a new penetration is needed after handover, it must get the same detailing before soil goes back.
Common mistakes on planted roofs
- Using a standard membrane. Ordinary rolls do not claim root resistance.
- Skipping the flood test. Finding a leak after planting is far harder.
- Weak upstand details. Roots and water reach edges first.
- No protection layer. Gardening tools and gravel can puncture the sheet.
- Leaving liquid flashings exposed. Impermax B 1K is listed for unexposed surfaces.
FAQ
Do I need a green roof anti-root membrane for planter boxes?
Yes. The HYPERFLEX-P20 Anti-Root sheet lists lining of flower boxes as a main use.
Can a protection board replace the anti-root membrane?
No. The board protects the membrane, while the membrane itself provides the waterproofing.
What about podiums with heavy landscaping?
Large podiums may suit a sprayed system instead. See our guide to podium and planted roof waterproofing with polyurea.
Can I add insulation to a green roof?
Yes, in a combined system. Our combo roof systems page explains the options.
Is there a mineral-finish anti-root roll?
Yes. The sheet says HYPERFLEX-P20 Anti-Root can come with a mineral slated top as a self-protected layer, subject to the system design. Slated rolls come at 4, 4.5 and 5 kg/m². Under soil, however, a protection board is still the safer choice.
Conclusion
A planted roof keeps the waterproofing wet and under attack from roots. A green roof anti-root membrane, a protection board, careful upstands and a flood test together handle that risk.
Target designs and executes roof waterproofing across Egypt. Contact our team to plan the build-up for your roof garden.
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