Lafarge - Villa Navarra

DUCTAL ®
The material was used 100%
for the roof structure, making the most
of all its properties.
P.10
DESIGN
A material used
sparingly to meet
the loads
VILLA
NAVARRA
Composed of 17 juxtaposed panels, the roof of the
Villa Navarra makes full use of Ductal®’s qualities. The
material is used 100%, as if left to its own devices, with
no other assistance than traditional reinforcing placed at the
upper part of the ribs. Even then the reinforcing is mechanically
redundant, used in the end as a safety measure, just as the
safety net protects the performing acrobat.
The roof, of optimal design and structure, makes use of a design
that faithfully follows the load lines with great economy of
means. “The material is placed exactly where needed in order
to be able to express itself,” enthuses Mouloud Behloul.
The architect’s son, the engineer Romain Ricciotti arrived at the
form through painstaking drafting, dictated by all manner of
constraints, starting with the most pressing: getting all the
materials to the building site in the middle of the countryside.
The road network is, therefore, the first factor behind the dimensions
of the roof, composed of modular, pre-fabricated parts.
The final module is a panel measuring 9.25 m x 2.35 m, whose
design is suitable for the spreading of the load in the planned
structure, which is made up of a plate of a constant thickness
edged by two lateral progressive inertia ribs, higher at the
supports and becoming gradually thinner, meeting the thickness
of the plate at the far ends. The ends have a clever open
design to save weight and to allow the light to enter this part
opened up as a porch. “The design produces an optimal
mechanic, which is not without similarities to steel forms, comprising
a web, wings or a purlin,” comments Romain Ricciotti, “and
this form is not the result of any particular design feature.”
A specialist in mathematical modelling, the young civil works
engineer almost goes on the defensive about having held the
pencil. “Structures behave as conceived and calculated,” points
out Mouloud Behloul, who accepts the pre-defining of the shape,
namely a plate edged by lateral ribs, “in as much as a structure
never imposes itself and is always a matter of choice,” so says
the engineer!
The decisive factors behind the size of the roof panel are, therefore,
its own weight, the allowable overload due to weather,
wind resistance and heat expansion, which it is likely to suffer
in a region subject to high amplitudes linked to sunshine and
high winds. These amplitudes are all the greater, as the surface
of the un-insulated roof is left bare, benefiting from the finished
look and the waterproof qualities of the Ductal® panels.
PRE-CASTED MODULES
The extremity of the modules
is open to add weight and make use the
light in this part with an open top.
“The aim to
reduce the impact
of the villa
on the site led
to the use of an
ultra-thin roof
made of Ductal®
which comes
to a thickness of
3 cm at its tip.”
P.11