01 May 1999
k. Vapor Retarders. With a SSSMR system with no roof deck, batt insulation faced with a plastic
film vapor retarder is frequently used. In a cool climate, the vapor retarder will be a facing on the bottom
of the blanket insulation; in a warm climate, the vapor retarder may be a facing on top of the blanket
insulation with a separate insulation support system. A slipsheet is required. Vapor retardancy can be
greatly improved by sealing all laps and penetrations to minimize air exfiltration.
Thermal Insulation and Heat Flow.
(1) Batt Insulation. When glass fiber blankets are used in SSSMR systems, they are supported
by draping them over the frame before the roofing is placed or by supporting them on wires or metal
bands strung beneath the roof panels. Slightly compressed batt insulation inserted between the substrate
and new metal panels helps dampen wind-generated noise.
(2) Thermal Spacer Blocks. At locations where the batt is squeezed between the frame and
metal panel (resulting in a loss of thermal efficiency) thermal spacers are used. These are relatively
incompressible blocks of polystyrene or polyisocyanurate.
(3) Limited Clearance. The height of the concealed clip limits the thickness of batt insulation that
can be installed.
(4) Rigid Insulation. When installed over a metal subdeck, noncompressible board insulations
such as polyisocyanurate foam are used.
(5) Insulation for Architectural Panels. For architectural systems, insulation may be placed
under the deck between rafters or as a rigid board on top of the structural deck.
m. Membranes. In this Chapter, the metal panels themselves are the roof membranes. Refer to
ASTM E1514 Standard Specification for Structural Standing Seam Steel Roof Panel Systems and CEGS
n. Roof Penetrations.
(1) Allowance for Thermal Movement. Lightweight skylights and lightweight HVAC curbs may be
supported by (and float with) the structural roof panels themselves. Structural members beneath the roof
panels support heavier air handling units. A double curb with a floating base and a stationary inner base
flashing attached to the panel, fixed to the buildings structure frame allows differential movement (figure
9-5). Large units may be mounted on pipe stands supported by other parts of the structure.
(2) Pipes. Pipe penetrations are flashed with rubber boots (figure 9-6). They should penetrate
the flat pan, not the raised seam. To minimize damage to metal roofs, large mechanical items should be
ground-mounted whenever possible.
o. Historical Roof Restoration. If the existing system is metal, new metal systems can duplicate the
color and seam style relatively inexpensively. Structural systems can be used as a retrofit over existing
systems improving slope and thermal efficiency.
p. Aesthetics. The numerous configurations of metal panel systems can achieve a variety of
appearances. Because panels often have a broad flat area they are prone to oil canning. Fluting
(deformations in the flat area between seams) are sometimes used to reduce oil canning effects.
Trapezoidal ribs may be either distinctive or distracting on highly visible applications. Trapezoidal rib
closure components at eaves may be unsightly.
q. Gaps, Flashings, Joints, Fasteners, and Sealants.