Growing sites for healthy city trees.

The goal with every Permavoid subbase system for trees is to create a multifunctional, layered urban design where it can grow as if it's in the forest, without using valuable space or hampering urban functioning. 


Trees for climate resilient cities.

The most beautiful place for a tree to grow is in uncompacted, natural circumstances, just like in a forest where rainwater can infiltrate and remains available for the tree. Organical material is converted into nutrients in a cyclic process and there is no major soil disturbance in, or compation of the rootzone. 

In cities rainwater is drained through often overloaded sewers. Consequently, trees lack water during growing season, the soil is compacted due to traffic loading and regular underground infrastructure maintenance damages roots. 


Urban foresters, architects and project developers experience a growing challenge to give both existing and new trees a chance in the city. The challenge for existing trees is to protect them in a ever changing city during construction and for new trees, creating sufficient growth space in the already busy landscape below ground is an increasing challenge.


Future-proof growing sites.


How does it work?

In order to create a growing site capable of facilitating healthy tree growth for many decades, fundamentals like water availability and loadbearing capacity must be considered. There should be enough water available during summer, but without flooding the root system during periods of heavy rainfall. Oxygen should be able to enter the soil, and carbon dioxide must be allowed out. City trees need protection from urban disruptions in the rootzone such as works on underground utilities and they need enough space to support growth and stability for their designed lifespan.

System functionality

With the Permavoid Capillary Irrigation System an artificial groundwater level is created beneath the rootzone, mimicking groundwater in a natural situation, enabling the growing site to capture, store and reuse stormwater for irrigation. In this arrangement trees prevent stormwater entering the sewer whilst simultaneously enjoying a water reservoir to sustain growth during prolonged dry spells.

The system is equipped with specially developed fiber columns that provide capillary transport of water from the Permavoid retention buffer to the rootable soil above. This natural irrigation system uses no energy and maintains a consistent soil moisture content such that the tree experiences a very stable groundwater level, allowing it to thrive in the urban environment.


Strong benefits for city trees.

The Permavoid solutions for future-proof growing sites provide enough space for unhampered tree growth for the lifespan of the tree, without sacrificing urban space needed for parking spaces, bicycle paths and walkways. The added goals of the future-proof growing site are to create energy neutral, drinking water saving system to sustain a healthy urban forest. 


This is achieved by combining and stacking different symbiotic urban functions: rainwater management, root growth, urbanity and the trees' ecosystem services are all realised in one and the same place.

Space for root development

In a situation where trees are expected to grow in a paved environment, compaction of the soil, superficial tree roots damaging the pavement and a greatly reduced gas exchange with the soil are known for growth-limiting factors. The Permavoid Sandwich construction eliminates these limitations by creating a stable and open raft beneath the pavement to ensure healthy roots.

Collect, store & return water

Just like in nature, we collect, store and naturally return water to the trees. Whether they grow in open soil or paved circumstances, trees become an integral part of urban rainwater management. By balancing stormwater availability and potential tree evaporation with irrigation based on natural capillary rise from below, we prevent flooding of the growingsite each time it rains.

Prevent pavement damage

Permavoid future-proof growing sites are designed in such a way that the tree no longer causes costly and potentially dangerous damages to the pavement. The nuisance of frequent and reoccurring pavement repairs become a thing of the past. With Permavoid roots are prevented to grow where they cause damage, seperated from the pavement with a layer of air, while providing them enough space to develop and flourish, away from the paved surface.

Cooling down

Healthy city trees reduce the urban heat-island effect, but the amount of water needed to be able to actually do so is often underestimated. Without sufficient water the tree cannot grow to its full potential to provide us with his much needed services to improve city life.

Rainwater as a valuable resource to help strengthen and future-proof the urban forest.


In a situation where trees are expected to grow in an urban and paved environment, compaction of the soil, superficial tree roots damaging the pavement and greatly reduced soil-gas exchange are known growth-limiting factors. The Permavoid Sandwich Construction eliminates these by creating a shallow, stable and open subbase for the hardscape to ensure optimum load distribution and high load bearing capacity, preventing compaction of the rootable soil volume underneath. The system is used in parking lots, residential areas, malls and bicycle paths, with a free choice of pavement options like block pavers, concrete or asphalt.

Trees are used to growing in open ground, but not in every situation healthy grow conditions are available. The balance between water, oxygen and organic matter. When these elements in the right balance, a healthy soil life can be present in which trees can live in symbiosis. Two solutions that allow trees to grow excellently in open ground are the Permavoid Sandwich construction and the Permavoid Capillary Irrigation System.

Now most of the high-end green roofs and podiumdecks have turned into Blue-Green roofs and podiumdecks, the possibillities to grow full size trees have opened up. The desire to have trees on raised structures is increasing.However concreet decks dictate a carefully chosen solution that will be enable waterstorage to irrigate the tree for a long period. Aside from the water supply, anchoring the tree is an important part of the design. The Permavoid solutions have proven to be able to fullfill these tasks in many projects. Full size parks on podiumdecks have been succesfully installed.

Existing trees are valuable. They purify the air and improve the living environment. The older the tree, the more efficiency can be achieved from the tree. That is the reason every step to change their existing habitat needs to be carefully considered.

Changes like water management, weight of backfill, compaction of the soil, aeration and others like choice of finishing permeable pavement or not will dictate the difference between failure or success of the project. The Permavoid solutions for existing trees will offer you the right tools to realize your projects.


Growing sites for trees are more and more becoming part of water management design. The cleansing capacities of special tree soils and the fact that trees need water is a promising marriage and makes the idea of an attractive proposal to be part of full water management design. However to succeed, there needs to be a balance between the stormwater input and the need of water for the tree. When all this is not balanced, the tree might drown and the stormwater system will fail.

The Permavoid legacy of over 20 years experience in water management and city trees, give you the garantee that designs and systems are fully in balance to create the optimum solution.

Inspiring projects

Get inspired by these projects.

From existing trees where a previously open growing site is to be converted into a hardscape, to new trees installed on a roof; we are proud of the projects we have realized with our partners throughout the years.

Have a look at a selection of the Permavoid tree projects installed globally and learn more about the technology in our brochure.

View all inspiring projects

We have built a reputation

Find your local distributor nearby.

Permavoid source control ensures that no precious water goes to waste by catching, storing and reusing stormwater for irrigation, evaporation and infiltration. Find your local Permavoid distributor here to learn more about the technology and become part of the international movement.