Frequently Asked Questions

How much does a vegetation blanket weigh and how much does a roof with vegetation blankets weigh?
A Sempergreen vegetation blanket weighs between 10 to 20 kg per m² depending on the moisture content of the blanket. This is without all the roof layers such as substrate, drainage layers etc. A roof with vegetation blankets normally weighs around 75 kilo per m², but with substrate plates the weight can be reduced to around 45 kilo per m².

What do vegetation blankets and other Sempervirens products cost?
If you want to receive information about what it costs to install a Sempergreen Vegetative Blanket Roof system, please get in touch by clicking the ‘contact’ button. We will answer your requests within one business day.

Is it possible to cover any roof with a roof garden (using vegetation blankets)?
If the roof surface is waterproof and roots cannot penetrate it, vegetation blankets can be applied to the roof.

Is a roof garden (with vegetation blankets) suitable for any roof?
A standard roof garden with Sempergreen® vegetation blankets weighs around 75 kilo per m². By applying substrate plates, it is possible to reduce this weight to as low as 40 kg per m². In addition, having (or installing) roof eaves is important to prevent the vegetation blankets from shifting or blowing away.

How long can you keep the vegetation blanket rolled up?
That depends on the temperature. The table below gives you an overview:

Below 0ºC:      7 days
1-10ºC:          5 days
11-20ºC:        2-3 days
20-25ºC:        2 days
Above 25ºC:   less than 24 hours

How many square metres of vegetation blanket fit on a single pallet?
A single pallet can hold approximately 50 m².

What is the maximum slope angle for constructing a roof garden?
Vegetation blankets can be applied to slopes of up to 85°. We have developed various systems that are applicable for different construction situations. Each system is suitable for a particular type of roof.

What sort of maintenance does a garden roof with vegetation blankets require?
A garden roof with vegetation blankets is a low-maintenance system. Once or twice per year the roof should inspected to check whether there are no undesired plants growing, which is unlikely due to the 85-95% coverage the roof offers once installed. Furthermore, drainage has to be checked for blockage because there must not be any still-standing water on the roof.

Does a roof garden with vegetation blankets require fertilization?
If a substantial extensive garden roof substrate (soil mix) was laid under the vegetation blankets, this may not be necessary. In some case however, it may be needed. Our advice is to fertilize one time per year, in the spring if one is looking for lots of blooms and the roof is visual (to be seen by people) vs. functional (mostly on tall roofs that never see visitors).
Note: if there are substrate plates (rock wool plates) under the vegetation blankets, you will have to fertilize at least twice per year.

Can you construct a roof garden with vegetation blankets throughout the year?
Yes, except for when it is freezing. This is because the vegetation blankets cannot be rolled up.