FAQs and answers

We learn every day. Sam Groofing is constantly developing. We take the opinions and feedback of our customers about the product very seriously. Below you will find FAQs and answers. If you have a pressing question that is not covered here, please contact us.

If you want to find something quickly, make a choice here…

green roofs in general
Can I save energy with a green roof?

Absolutely. In summer the sedum will block heat, making a cooling installation redundant (thereby saving on extra electricity). Black roof covering gives off 80 degrees, a sedum roof 38 degrees

Is a green roof suited for every type of roof?

A Sam Groofing finish can be applied to any type of roof. On flat roofs by means of drainage panels and pockets; on sloping roofs using industrial-grade Velcro. With currugated roofs and profiled steel roofs this is possible up to a 45 degree gradient.

We are going to redesign our garden. Can we include the roof in the design?

This is an excellent idea. The diversity of sedum species in our roofs will add an extra dimension to the garden.

I live in a city. Can I have a green roof?

In cities and towns in particular it is sensible to create cool spots and support biodiversity.

Do I contribute to a better environment if I have a green roof?

100% yes. Because it boosts biodiversity, serves as water buffer, reduces heat and – in the case of Sam Groofing – uses recycled products. And when the time has come to replace or scrap the roof, Sam Groofing is fully recyclable.

How are the edges of a green roof finished?

This depends first of all on whether the roof is flat or sloping. In case of a sloping roof the architect/contractor is consulted, to stay in line with the design of the building. The standard edge finishing for a sloping Sam Groofing® green roof is a black aluminium L-profile. To ensure proper drainage this profile has been perforated on the gutter side.
On flat green roofs the edges are usually finished with gravel. But here also the edges may be trimmed with aluminium L-profiles. With or without perforation.

I have solar panels. Can I have a green roof as well?

When combined with solar panels, sedum will increase the panels’ efficiency. The sedum plants have a cooling effect. The cooler solar panels are placed, the higher their output. Common arrangements are: pockets placed next to the solar panels; or solar panels on one side, green roof on the entire other side of the roof. Sam Groofing can be applied to any roof surface, regardless of its exposure to sunlight.

Sam Groofing - green roofs
About the purchase
Don't the (sedum) plants get damaged during transport?
No. The unique shape of the pockets, together with special recesses in the drainpanels, prevent the plants from getting damaged during transport. In addition, the roots have a special casing that anchors them firmly in the pockets. Moreover, sedum plants are very sturdy by nature and therefore less vulnerable. This being said, it remains important to take care while unstacking the pockets and make sure that the plants don’t get damaged.
Are Sam Groofing® pockets available in different sizes?
For flat roofs we work with a standard size of c. 100 cm x 40 cm. Joins to roof penetrations (pipes, skylights, etc.) and to the eaves are made with gravel. For sloping roofs the standard size is also c. 100 cm x 40 cm. To provide these roofs with full cover we offer so-called ‘fitting pockets’. These are 20 cm wide and are available in different lengths (100, 80, 60, 40 and 20 cm). Where necessary the fitting pockets will be made exactly to measure ‘on the job’. This will ensure neat transitions to, for instance, chevrons, valley rafters, windows and dormers.
Can you also take care of transport?
Of course we can. We use a regular partner/transporter who is well-equipped to deliver our products. Collection at our facilities is not possible.
Why should I pay more for your new product?
You pay for the quality/price ratio. Sam Groofing is a lightweight system with a larger and more diverse plant assortment.
Can I get a quotation without gravel? This I can buy cheaper myself.
That is certainly possible. Please mention this when you request a quotation.
Are there subsidies for improving home sustainability with a green roof?

In most cases subsidies are available from local councils and water authorities for sustainable improvements and for sewer separation. Every council or authority has its own conditions and subsidy rates. See www.samgroofing.com/subsidies………..

We are currently renovating out home. Can the costs of a green roof be included in the contruction deposit loan?
Yes, this possible. It is seen as part of the home.
About the plant assortiment
What does the system look like in winter, spring, summer and autumn?

Not every sedum species in our pockets is perennial or evergreen. Because of the great diversity of species this balances out prefectly. From April to October the colours will jump out at you, changing from moment to moment, as there are at least 12 different sedum species represented in the pockets. Growth habits and seasons also differ. One species will bloom at a certain time, another species on another day. This compares to a standard garden on the ground.

How is Sam Groofing different from ordinary sedum mats?

A traditional sedum mat is a relatively cheap product. To manufacture it profitably, 6 to 8 fast growing species are selected. In most cases they are exclusively ground cover plants. Higher growing species are rarely used. They grow more slowly and have a hard time developing in a thin sedum mat. Higher growing species are also liable to break when the mats are rolled up for transport. All in all this causes sedum mats to have a monotonous and low look.
Our green roofs will permanently sustain a much larger number of plants than ordinary sedum mats, including higher growing species. This guarantees a much richer and more varied Sam Groofing® green roof.

What are the differences between the various sedum species?

We divide the range of plants into three groups:

  • Evergreen and ground covering
  • Semi perennial and ground covering
  • Deciduous and solitary

The plants vary as to flowering season, inflorescence, colour and shape. There are fine-leaved, evergreen ground cover species, But also solitary, broad-leaved and higher growing species. Up to 30 cm and more. Some have yellow flowers. Others white or red. Several species shed their leaves in winter.

Can other plants be added to the mix in Sam Groofing pockets?

Yes, Hhis is possible – in principle. However, we recommend not doing this. The range of our sedum species has been carefully tailored by our own breeder. This guarantees a beautifully varied green roof with different flowerings, seasons and colours. Adding other plants may disturb the carefully created balance. In large projects and with large volumes the customer’s specific wishes regarding composition and variety may be taken into account.

How many sedum species are there to choose from?

By default Sam Groofing consists of a very extensive range of at least 12 to 16 different sedum species. They have been carefully chosen and matched. Plug plants were selected because they help maintain a much wider variety of sedum species over the years than can be found on regular roofs of sedum mats. In nearly every situation this range performs extremely well.
In large projects and with large volumes the customer’s specific wishes regarding composition and variety may be taken into account.

Can a vegetation roof be 'custom made'?

Yes, But only with large projects and large volumes. And always in consultation with our own breeder. Because we want to be convinced that the chosen range is well matched and will ensure a beautiful green roof for many years to come.

Is variety of sedum species necessary to improve biodiversity in a green roof?

Absolutely! By definition, greater variation in sedum species means greater biodiversity. In addition, a wider assortment with different inflorescences and flowering seasons leads to a greater diversity of insects. In this way, for instance, we can support and advance the bee population.
In the future we shall further boost biodiversity by employing e.g. ornamental grasses and herbs in our green roofs.

product specifications
The water storage capacity (retention) is 30 liters per m² by default. Can this be increased?

Yes, On flat roofs it is easy to expand water retention. Sam Groofing® drainpanels are stackable. Extra drainpanels can be placed under the roof pockets. With every extra drainpanel the water storage capacity increases by 25 liters per m².
For sloping roofs we advise against increasing the water storage capacity. The shearing forces and roof load may become excessive. That is why Sam Groofing® does not support this possibility. Where it is necessary or desired, we recommend you realise your extra storage capacity for water from sloping roofs in or around the building.

Is it possible to calculate precisely how much rainwater is absorbed by a green roof, so that it does not end up in the sewers?

No. Unfortunately there is no way to calculate this with any degree of precision. It depends on the amount of rainfall per occasion, the interval between showers and the evaporation in between showers. In ordinary circumstances the pockets can retain 30 liters of water per m². When rain falls shortly after full saturation, absorption capacity will of course be reduced. After a longer interval it will go up again. What is certain is that a green roof retains much more water than a regular (tiled) roof or a regular bitumen, PVC or EPDM flat roof.


In the future capturing rainwater locally will become ever more important or even legally required. Is this also possible with a green roof?
This is definitely possible. See the answers to the previous questions. We are also exploring additional possibilities for processing water released by our roof system.
How do the sedum plants root in the Perlite substrate?
At the time of planting the sedum plants are given a first supply of nutrients that will gradually be released in the course of the first year. This stimulates root and plant growth. Perlite is characterised by its good perviousness to roots. The end result is a comprehensively rooted substrate layer. 
Can the roots penetrate the bottom fabric?
The bottom fabric of the pockets (the needle felt) has been covered with a root protection layer (DuPont™ Plantex® gold) on its inside. No roots will penetrate this layer. H owever, we cannot exclude the possibility that the roots of seedlings (seeds carried by wind) will grow through the seams of the pockets. For that reason we always recommend using a root-proof roof cover. Particularly on sloping roofs.  If the existing roofing on a flat roof is not yet root proof, a root protection fabric should be applied first. On flat roofs such a fabric may also serve as extra protection for the roof surface. We can supply these fabrics when required.
Are the spaces between the drain panels under the pockets susceptible to weed growth?
No. The absence of light will prevent any weeds from growing under the green roof, so that the drainage capacity remains unchanged.  For a beautiful green roof and continued good drainage, we do recommend that you service your roof twice a year. Specialised horticulurists offer reasonably priced maintance contracts that will guarantee a permanently beautiful green roof and dependable irrigation and/or drainage.
Why is it that the pockets weigh no more than c. 5 kg at the time of installation?

Light waste flows (‘Post Consumer Waste’) have been combined with a unique design. This results in a very light, but still remarkably sturdy drainage panel. In addition, the Sam Groofing® pockets are filled with Perlite. A very light substrate for plants that is regularly used in food production horticulture. When they are planted, the sedum plugs are given a carefully calibrated quantity of water. As little as possible to minimize weight but enough to see them through transport and construction.

What does a green roof weigh?

At its heaviest, the pockets are approx. 44 kg per m² when they are completely full of water. This will be suitable for almost any kind of roof. At the time of installation the pockets weigh 5 kg each. The lack of weight makes mounting the roof very pleasant.

Will the roof not be too heavy when a layer of snow starts melting?
Fully saturated, a Sam Groofing® green roof weighs no more than c. 44 kg per m², making it one of the lightests of its kind. In structural calculation for buildings the added load of snow and/or melt water is taken into account. The structure has to be strong enough to bear the total load. This is no different for a Sam Groofing® roof than for any other green roof system.
Do you have a standard calculation to determine a roof's load bearing capacity of a roof?
No. Unfortunately not. The load bearing capacity of a roof depends on many factors. Consequently, it needs to be determined by an expert, such as an architect, builder or structural engineer. In case of doubt we can refer you to specialized engineers, who can determine, in consultation with the client, whether a roof will bear the load of our green roof.
About the effects on the surroundings
How is the fire safety of the roof warranted?
Internal company tests show that fire safety is guaranteed. Firstly, the green roof will be moist for large parts of the year. Which makes it resistant to flying sparks from outside. Next, moist roof coverings are fire retardant. Finally, the Perlite in the pockets is also fire retardant. Perlite is used in industrial applications for the purpose of fire retardancy.
In the course of 2023 the fire safety will be tested and certified by external parties.
Is a green roof susceptible to wind?

No. This has been shown in internal company field tests.
On sloping roofs the pockets are firmly secured to the roof construction by means of industrial Velcro. On flat roofs the elements are connected by dovetail joints. Also, the growing sedum plants will form a stable interconnected vegetative cover. Finally, practice has shown that green roofs are much less sensitive to ‘wind suction’ than regular roofs.
In the course of 2023 the wind sensitivity will be tested and certified by external parties.

To what height can Sam Groofing® green roofs be applied, with reference to increasing wind load?

In principle all green roofs are relatively unsusceptible to wind suction because of the sedum. This is no different for the Sam Groofing® green roof. Therefore it can be applied at greater heights. If required, the panels and pockets may be either joined together or attached to the roof surface with industrial Velcro. This will further increase wind resistance.

Does a green roof serve as an insulator?

During summer a green roof will be moist most of the time. The moisture evaporates in dry, warm periods, keeping the roof temperature down. Also, the green roof itself has a cooling effect. Because the plants absorb heat during the day that is given off at night. Next, the air buffers in the substrate afford insulation. Finally, many traditional roofs are covered with dark tiles. Solar radiation makes these roofs much hotter than a green roof. All these factors combine to keep the building itself cool.

Can you indicate precisely how much CO2 is absorbed by a green roof and how much oxygen (O2) it produces?

No. Unfortunately this is impossible. It strongly depends on the weather and the resulting growth parameters of the sedum roof. As we all know, the weather varies greatly. Wageningen University has calculated that 20 m² of green roof on average produce sufficient oxygen for one person. Because of its wider plant range a Sam Groofing® green roof will capture more CO2 than regular roofs of sedum mats.

What is the material that the drainpanels and the frame are made of?

We made the deliberate decision to manufacture the drainpanels under the pockets out of ‘Post Consumer Waste’. This is waste from the end user (such as organic waste, waste paper and plastic packaging that a consumer throws in the bin). The frames are made from ‘Poly-Al’. These are waste flows from, among others, milk and juice cartons and recycled shampoo bottles. This way we contribute to meaningful waste recycling.

Using sedum plug plants requires a much smaller growing surface than regular sedum mats. Why is this?

We made the deliberate decision to work with so-called ‘plug plants’. These are either individual sedum plants or bunched mixes of several plants. Our breeding spaces contain 450 plug plants per m². These are planted in the pockets with a density of 30 plants per m². This way 1 m2 of growing surface is turned into 15 m² of green roof. Every m² of breeding space is used at least twice a year, so that we can turn 1 m² into more than 30 m² of green roof per year. In regular sedum mat cultivation 1 m² of cultivation space becomes 1 m of green roof. This makes our demand on expensive and scarce cultivation soil considerably lower and with it our environmental footprint. To build on this even further, our plug plants are grown chemical-free.

Is the top side of the pocket sensitive to sunlight or birds?

No. The irrigation fabric (top side of the pocket) remains UV stable for at least 8 years, but long before that it will have been covered by the sedum and not be exposed anymore to solar radiation. The fabric is also resistant to bird pecking. A special casing around the roots of the plug plants anchors them firmly in the pockets. This also minimizes the risk of damage inflicted by birds pulling on the plugs.

How do you make sure that your green roofs are manufactured sustainably?

Our production location is right in the middle of the Netherlands. Centrally located for our, mainly Dutch, suppliers and for our customers. Our internal transport equipment is fully electrical. Our production line was designed in such a way that there is hardly any waste.

About dealing with the roof in practice
Can you stand on the pockets?
Yes, You can walk on a green roof, but it is advisable to restrict this to the servicing in spring and autumn. During the first year of development we recommend that you walk cautiously, so as not to damage the sedum. As the vegetative cover continues to develop, it will become less vulnerable.
Is it easy to replace a sedum plant in the pocket?
Yes, No problem at all. This is usually done during the regular servicing of a green roof. If, in spite of all precautions, a bare patch has formed, new plugs are easily planted to fill the gaps.
Can I buy single plug plants?
Yes, you can. For the maintenance of Sam Groofing® vegetation roofs.
What are the maintenance instructions?
For this we would like to refer you to the practical guide on this website.
Is a green roof easy to maintain?
You can see the maintenance of this green roof as common garden maintenance. Take out weeds and nourish by adding organic fertilisers.
Is it a problem when moss grows on the green roof?
No, this is not a problem. As long as the roof is not yet fully grown this may happen. You can choose to control it. There are biological products available. But moss does not hamper the sedum at all. For this reason we prefer letting the green roof close its cover at its own pace, after which the sedum will automatically replace the mosses.

If you have any other questions, feel free to ask our specialists.