Designing for Building Maintainability - Effective Building Maintenance: Protection of Capital Assets - page 139

down the drainage cavity and drain to the outside, not to the inside of
the building.

Fenestration
Fenestration represents a “hole in the wall” through which water,
water vapor, and air can enter a building. Windows, even the very best,
do not have a thermal performance that even approaches that of a well-
insulated wall; have you ever seen an R-30 window? So, unless very
carefully designed, almost all fenestration represents increased energy
inefficiency for the building envelope. Tominimizethesenegativeimpacts
andthemaintenanceassociatedwithdealingwiththem,thequantityoffenes-
trationshouldbeheldtotheminimumrequired .
Next, avoid operable windows. Operable windows typically result
in increased infiltration and resulting moisture intrusion, and tend to
leak over time, requiring routine maintenance. Fixed glazing systems
avoid many of these problems.
But, even with fixed glazing, careful detailing of the window in-
stallation is required to prevent water intrusion. Both the tops and bot-
toms of windows must be flashed. Flashing over the window top trim is
required. In all cases, windows should be recessed in the wall to provide
a drip edge along the top and/or provided with a specifically designed
drip edge. Pan flashing is a highly recommended method for creating an
under-window “gutter” to redirect any leaking water to the exterior.
The problems with window-wall systems are even more complex.
Unlike traditional curtain wall systems that span floor to floor with at-
tachments outboard of the slab edge, the traditional window-wall sys-
tem is designed to bear on the slab edge and extend up to the underside
of the slab edge above. In some systems, a slab band cover is provided
to give an appearance similar to curtain wall. Although there are many
variations, the typical window-wall system is defined by the following
features:

• Window extrusions used to span from floor to floor in a pre-man-

ufactured unitized system typically up to 6 feet in width.

• A coupler connecting the vertical mullions of each window-wall

unit, either as a male-female coupler integral to the vertical mul-
lions or as an independent coupler.

• Window-wall systems bear on the slab edge at the floor level and