The second half of the same task
Green roof: what lies beneath the vegetation
A green roof is not just turf piled onto cardboard. It is a layered system where each layer has a specific function, and if one is missing, the result will only become apparent three years later as a leaking ceiling.
We treat green roofs as the second half of the same task: what to do with the water that falls on your property. A tank retains it underground, a green roof retains it above ground and evaporates it, reducing discharge into the sewer system, which in Prague is now also becoming a financial issue.
Most commonly, this involves an extensive roof on a garage, extension or pergola: low parapets, a layer thickness of around 10 cm, and minimal maintenance. An intensive roof with a garden and shrubs is a different league. It requires a structural assessment and regular care like any garden.
What constitutes the stratification, from bottom to top
- 06
Root-penetration resistant waterproofing
Ordinary cardboard is not enough: sedum roots will find every joint.
- 05
Protective and separating layer
Protects insulation during installation and against mechanical damage.
- 04
Drainage and water storage layer
Noppings foil or gravel. Retains water reserves and drains excess.
- 03
Filter fabric
It prevents fine substrate particles from clogging the drainage.
- 02
Vegetation substrate
Not garden soil: lightweight aggregate with minimal organic content, 8–12 cm for extensive roofs.
- 01
Vegetace
Rough-sown carpet, seed sowing or pre-grown mats. Carpet is more expensive but ready immediately.
The order is from top to bottom, as seen when viewing the finished roof: the numbers correspond to the build-up from the bottom up, as installed.
What the structure must support
Saturated extensive layers weigh approximately 100–150 kg/m². This is a load that most concrete ceilings above garages can handle, but a wooden pergola structure or an older extension cannot. A structural engineer’s assessment is a mandatory stop for wooden structures, not a formality.
The second factor is the fall. A green roof can be installed on a flat roof, but it requires reliable drainage and an inspection shaft. Without one, the first blocked inlet will only be noticed when a wet patch appears on the ceiling.
Subsidies
Prague gives the green light to the roof up to 200 000 Kč for a detached house and up to 400 000 Kč for a flat, always at most half of the documented costs.
Terms and conditionsFrequently Asked Questions
How much does a green roof cost?
An extensive layering system including vegetation costs approximately 1 500 to 3 000 Kč per m² depending on the type of vegetation and whether the waterproofing is also replaced. For a small garage, we are talking about tens of thousands; for an apartment building, hundreds of thousands, and it is precisely there that the subsidy is most interesting.
What subsidy will I receive for a green roof?
In Prague, up to 200 000 Kč for a detached house and up to 400 000 Kč for an apartment building, always covering no more than half of the documented costs. Outside Prague, the interest-free loan from Nová zelená úsporám remains available. Details and deadlines are on the subsidies page.
What maintenance does an extensive green roof require?
Twice-yearly inspection of drainage outlets and removal of invasive woody plants. Hellebores are not mown or watered, though in the first year after planting they will appreciate watering during dry spells.
Do you want to know if your roof can support it?
Tell us the area and construction type. We will advise whether an extensive layer is sufficient, if a structural assessment is required, and what subsidy you could receive.