Trees Through the Roof and in Courtyards: What This Involves

We are increasingly seeing it in deliveries and projects: trees as part of a building. They are usually located in a courtyard, patio, or covered outdoor space, and therefore largely outdoors. The building has been designed around the tree, with the trunk passing through a roof, overhang, or terrace deck. Sometimes construction takes place around an existing mature tree. In other cases, the large tree is planted first and the building follows afterward.

A clear trend underlies this demand. Cities are becoming denser, and designers want to incorporate mature greenery within a building’s footprint as part of how a place is used. A courtyard with a real tree turns an enclosed building into a place where people enjoy spending time. This requires a tree that looks mature from day one, and therefore a large planting size at installation.

The architecture and accompanying renderings for these developments often look grand and green. In such a rendering, the tree is always fully grown, and the contrast between the building and the greenery beside it is precisely why a large planting size is requested.

That difference between indoors and outdoors determines almost everything that follows. A tree that is largely outdoors grows under normal outdoor conditions. Very different conditions apply in an enclosed, heated space. Below are the factors that are decisive during the design phase.

Where the Trunk Passes Through the Roof or Terrace

The defining detail is where the trunk passes through the roof or terrace deck. Coordinate this with the structural engineer at an early stage. The trunk gets thicker every year, so make the opening generous or allow it to expand as the trunk grows. And once the crown is exposed, the tree moves in the wind: the edge must not rub against the bark, and water must be drained away along the trunk.

Such a tree often falls outside standard nursery forms. Consider a branch-free trunk of more than 4 meters, with a crown of 3 meters above it.

Root Space and Soil

If the tree is already there, protect the roots. A changed soil level, compaction by machinery, or paving over the roots causes damage that may not become visible until years later. Keep this area clear and uncompacted.

If a new tree is planted in a planting bed or planter, the rootable volume sets the upper limit for its ultimate size: if it is too limited, the tree will dry out more quickly. Once construction is complete, this space is fixed. A rule of thumb is approximately 1 m³ for every year the tree is expected to remain in place, so allow for several tens of cubic meters. Also provide a dedicated water supply and drainage.

Light

A tree crown needs light, including in a courtyard. With an open patio or a roof with a large opening, this is rarely a problem. If the walls are high and opaque, the opening above the tree becomes especially important. The farther the tree is from that opening, the less daylight the crown receives. Pay particular attention to winter, when daylight is at its lowest. Position the tree as close as possible beneath the opening, and in low-light conditions choose a species that tolerates this well.

Reflection of sunlight from building facades can, in turn, create a magnifying-glass effect, causing leaves, the trunk, or the litter layer to burn.

Trees in a Heated Indoor Space

If the tree is largely outdoors, in a courtyard or beneath an open roof, it lives under normal outdoor conditions and the standard assortment is suitable. This only changes in a fully enclosed, heated space.

Deciduous broadleaf trees from our climate enter dormancy in winter and need a long period of cold to remain dormant and leaf out normally in spring. If they do not receive this cold, as in a heated space, the tree leafs out irregularly and does not survive. For such locations, several evergreen species from warmer regions that do not need cold winter dormancy and tolerate dry air are suitable, such as Olea europaea and Quercus ilex. They like warmth, but also need a bright location close to the glass. Warm and too dark is unsuitable for every tree.

Installing Large Trees During Construction

Mature greenery requires large trees, and they must not only fit the design but also be able to reach their location in practical terms. The load-bearing capacity of the structure, the delivery route, and crane operations often mean that the tree is placed early in construction, while the space is still open. The larger the tree, the earlier this must be incorporated into the planning.

Where We Become Involved

Most of the work takes place during the design phase, long before delivery. This is when decisions about the site, trunk opening, and root space are finalized. Our advisors help determine the species, size, and site, and work with the architect and structural engineer to assess what the tree needs in that location to establish successfully, from the first sketch to the day it is planted. With the enormous selection of large sizes from our own cultivation, there is almost always a tree that suits the location.

Is there a project in which a tree plays a role through or within the building? Present it to us at an early stage, and we will help assess what is feasible.