Agriculture Reference
In-Depth Information
Living roof scenarios include the construction of a new building project, where
the living roof is designed into the project from the outset and the retroit of a
conventional roof, where a living roof is constructed above an existing roof
structure. At the outset of designing a living roof, both new and retroit types
follow similar planning considerations. In both roof scenarios, the architect, with
the approval of the client, supplies concept drawings of the proposed or existing
roof and its structure to the landscape architect, structural, mechanical engineer,
envelope consultant and roof installer. It is important that all consultants work
together from the outset of the project.
3.3.1 Building structural capacity
Structural loading is one of the main factors controlling the feasibility, cost and
design of a living roof, whether the project is a new or retroit living roof. Assess-
ing a roof's structural capacity requires early coordination among the design con-
sultants, as it is often the most limiting design factor thereby affecting almost all
other elements of a living roof project. Planning a living roof should be a
collaborative process to ensure building and public safety while satisfying living
roof project objectives. Otherwise, unnecessary extra planning cost and reduction
in design freedom may occur, as the example of Potsdamer Platz explains.
The Potsdamer Platz in Berlin showcased a signiicant living roof component
in the multi- building project. Objectives of this project were to collect and recycle
stormwater, reduce runoff and enhance the newly developed urban space with
visual richness, including varied vegetation from shrubs to large trees. While the
project was successful on these fronts, the living roof design did not reach its full
potential in terms of rooftop experience because a landscape architect was not
consulted from the inception of the design. This occurred because the architects
and structural engineers neglected to inform the client regarding the necessity of
the landscape architect. The architects and structural engineers had designed and
calculated the load-bearing capacity of the roof on most of the buildings without
including living roof designs and their loads. Consequently, a desire to save costs
in structural reinforcement (having not been worked into the budget) limited the
point load capacity prescribed by the structural engineer. This in turn limited the
use of trees, other intensive vegetation, and other design features that
structurally behave as point loads. Freedom of planting design was undermined,
and consequently, many opportunities were missed in creating a varied rooftop
experience.
New extensive living roofs can be accommodated in building design for a
minor additional cost. In many cases, the weight of an extensive living roof is
similar to the weight of a ballasted roof. Retroit projects need to consider fore-
most the bearing capacity of the structure. Due to structural loading require-
ments, only extensive living roofs are typically suitable for retroit installation.
Such considerations also bear on pairing structure with function: for example, it
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