What does a green roof cost and what should you check first?
By Hovenier Hoofddorp · Updated July 19, 2026
An extensive green roof (sedum) costs about €45–€100 per m² installed and suits most sheds, extensions and garages with a flat or gently sloping roof. Check two things first: the load capacity (a saturated sedum roof weighs 60–120 kg per m²) and the condition of the roofing — a green roof then protects that roofing and roughly doubles its lifespan. Many Dutch municipalities subsidise green roofs.
How is a sedum roof built up?
- Root barrier protecting the roofing.
- Drainage layer that stores a buffer and sheds surplus rain.
- Filter fleece and 4–6 cm lightweight substrate (not garden soil).
- Sedum mats or cuttings — drought-proof succulents flowering from May to September.
With a thicker substrate (10–15 cm) a wildflower roof is possible — more insect value, more weight, stronger structure required.
Can my roof carry it?
- Concrete roofs (garages, extensions): almost always fine.
- Timber shed roofs: usually fine with a lightweight system (from ±45 kg/m²), but have older sheds and long spans assessed.
- Sloping roofs up to ±35°: possible with anti-shear systems; beyond ~20° costs rise.
- Roofing older than 10–15 years: replace it first — the green roof will then protect the new layer against UV and temperature swings.
What does it deliver and what maintenance does it need?
- Water buffer: 20–30 litres per m² retained per rain event — exactly what polder drainage systems need.
- Cooling: the room below stays noticeably cooler in summer.
- Biodiversity: flowering sedum feeds bees and butterflies.
- Subsidies: many municipalities contribute (Haarlem, for example, €25–€35 per m² plus up to €500 for a water butt). Check your municipality's scheme.
Maintenance is modest: remove seedlings and clear edges/outlets twice a year, plus a spring sedum feed. We fold this into regular garden maintenance.
Frequently Asked Questions
What does a sedum roof on a 10 m² shed cost?
Roughly €450–€1,000 all-in, depending on system and access. With municipal subsidy where available, the net cost drops substantially.
Do I need to water a green roof?
Only in the first six to eight weeks and during extreme drought. Sedum is a succulent; turning red in a hot summer is a natural drought response — it greens up after rain.
Do I need a permit for a green roof?
Usually not for an existing shed, garage or extension — you are not altering the structure. Exceptions: monuments and protected townscapes. We check the Omgevingsloket for you if in doubt.
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