Designing for Building Maintainability - Effective Building Maintenance: Protection of Capital Assets - page 147

a. A built-up roof application does not require a vapor retarder,
as the roof membrane serves a dual function as water barrier
and vapor barrier.
b. If a single-ply roof application requires a vapor retarder, it
should be located between the insulation and membrane. If a
single-ply roof application is installed over an existing built-
up roof, a vapor retarder is not required, as the existing built-
up roof will serve as the vapor retarder.
4. Roofs and flashings normally require “blocking” for vertical and/
or horizontal alignment or for close off. Typically, the blocking
specified is treated wood. Alkaline copper quat (ACQ-D) and
copper azole (CA-B) are the two primary preservatives that have
replaced chromated copper arsenate (CCA) in pressure-treated
wood products. Recent research shows that these new preserva-
tives are 2-5 times more corrosive to galvanized steel fasteners,
because of their high concentrations of copper, due to galvanic re-
action. Highly galvanized (G-185) hot-dipped or powder-coated
fasteners and connectors must be used to prevent premature con-
nector failures that result in roof leaks.
5. Flashing design should comply with ArchitecturalSheetMetalMan-
ual , Fifth Edition, Sheet Metal and Air Conditioning Contractors
National Association (SMACNA). Galvanized steel flashing, unless
hot-dippedgalvanizedafterfabrication,shouldnotbeusedinhot,humid
climatesbecauseofproblemswithcorrosion(especiallywithtreatedwood
blockingornearsaltwater)andpainting . It is always better for main-
tenance to use copper, stainless steel, or lead for flashing; do not
use flexible membranes.
Interior Construction and Finishes
There are two considerations relative to interior construction and
finishes, the first is design life and maintainability, while the second re-
lates to some finishes, such a vinyl wallcovering, oil-based paint, etc.,
that can act as vapor retarders.
Gypsum wallboard (GWB) is a common interior wall material. But,
GWB is much easier to damage than concrete masonry units (CMU) and
should not used to enclose high use areas such as corridors in schools,
hospitals, etc. Interior doors should always be the solid core type; hol-
low-core doors are far too easy to damage. Designers should specify