SYSTEMS/GLASS AND METAL CURTAIN WALLS
4.1 GLASS AND METAL CURTAIN WALLS
The airtightness of glass and metal curtain walls is provided by the glass and metal panels and the
aluminum or steel tubes that comprise the system. Figure 4.1.1 shows the basic components of a
curtain wall system employing a pressure equalized cavity to control rain penetration and to protect
the air seals. The thermal insulation system consists of the insulation behind spandrel panels,
sealed double glazed windows, and thermally broken mullions. Continuity of the air barrier is
maintained at the mullion air seals and the interfaces between the curtain wall and other envelope
systems. The design of thermally-broken mullions are crucial elements in maintaining the continuity
of the insulation system.
Figure 4.1.1 Glass and Metal Curtain Wall (Ganguli)
Curtain wall systems have both advantages and disadvantages over other envelope systems, many
of which relate to the thermal performance of these systems. The advantages include the following:
weather conditions have relatively little effect on construction, most systems are self-weeping, they
generally have a high quality appearance and relatively fast erection, and much of the engineering
can be done by the curtain wall supplier. The disadvantages include: a high level of exterior
maintenance is required for cleaning, condensation can result on cold parts of the system if
adequate thermal breaks are not included and a relatively high cost. The American Architectural
Manufacturers Association (AAMA) has developed numerous manuals on curtain wall design,
installation, testing and performance requirements. The performance and testing requirements
addressed by the AAMA documents include air leakage, water penetration, condensation
resistance, thermal transmittance and structural performance. While curtain wall system design is a
well developed area, the thermal performance of these systems can be compromised by
discontinuities in the air barrier and thermal insulation systems at mullions and at interfaces with
other envelope systems.
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