SYSTEMS/STONE PANELS
Design Information
Information on the design of stone walls is available from the Indiana Limestone Institute of
America, Inc. and the Marble Institute of America. Their publications cover a wide of range of
information including material properties, load calculations, recommended practices for erection and
various details for parapets, anchors and joints. The provision of thermal integrity with continuous
thermal insulation and air barrier systems is not explicitly addressed in these documents.
Bortz discusses some of the problems associated with stone curtain wall systems in the field,
particularly thin veneers, but these issues are relevant to most stone wall systems. Material
problems of weathering, staining, moisture permeability and structural integrity are important issues,
particularly with thin veneers. The design issues raised by Bortz include the need to adequately
accommodate differential movement between panels and between panels and their supports.
Otherwise, cracking and other serious structural problems can result. Proper design for wind loads
is an issue of obvious importance. Panel joints, along with systems for drainage and weeping, must
be properly designed following the recommendations contained in industry design manuals. Bortz
discusses problems of panel anchorage, pointing out that stone is brittle and sensitive to stress
concentration. The final area of field problems discussed by Bortz is that of construction technique
including the failure to remove temporary shims and spacers, and careless caulking and mortar
droppings that lead to the clogging of drains and weepholes.
Because stone itself is air and watertight, the panel joints become the critical elements in the
system when using the face seal approach in a stone facade. Smith points out that good air and
water-tightness performance can be achieved when proper detailing is employed and realized during
construction. In addition, the inevitable penetration of the facade by water must be acknowledged
and dealt with through water deflection, collection and drainage systems. If instead a rain screen
approach is employed, an air barrier system is required elsewhere within the envelope.
Thermal Insulation
The issues relevant to the insulation of stone panel walls are similar to those for other panel
systems, with insulation system continuity being the key. Benovengo points out some important
issues for the insulation of stone trusses, specifically that these panels can be preinsulated before
being installed in the field. Installing insulation on the interior of the panel has the advantages of
running continuously outboard of the structure and of the better quality achievable with off-site work.
However, this approach is problematic in terms of performance because the wall will likely
experience some water penetration, which can affect the performance of the insulation material.
During construction, window openings are generally vacant for some time before glazing. This
allows rain to soak the insulation, ruining the thermal barrier. Insulation at columns and spandrels
may not be accessible for replacement when this occurs. Therefore, temporary protection of the
insulation is essential during construction.
Benovengo and Gulyas advise against locating the insulation directly on the backside of the stone
since it will result in draining water being held in contact with the stone for long periods of time, and
this can weaken the stone.
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