CEMP-ET
TI 809-53
01 May 1999
a. Sealants. The sealing compound must be a nonskinning, noncuring, nonhardening type
compound (typically butyl) acceptable to the panel manufacturer. It must be kept under compression
within the joint by either seam folding or by use of mechanical fasteners (screws). Location of the sealant
must be on the weather side (i.e., down-slope side) of end joint fasteners (figure 9-9).
b. Joint Movement. Differential thermal movement must not occur between the components of
sealed joints. Expansion joints are typically required when runs exceed 40 m (135 ft.) for steel and 30 m
(100 ft.) for aluminum.
c. Oil-canning. Some distortion of metal panels is unavoidable. Oil-canning can be minimized by
proper adjustment of the roll forming equipment. Transverse embossing is available on some panel
configurations.
d. Noise. Noise caused by wind, hail, or thermal movement can be muffled by inserting blanket
insulation.
e. Air Exfiltration.
Seal all laps and penetrations of faced blanket insulation to minimize air
exfiltration.
f. Minimum Slopes for Cold Regions. In cold regions, EI 01S908 recommends a minimum slope of
12% (1-1/2 in. in 12).
9-4. CONSTRUCTION CONSIDERATIONS.
a. General. Each pre-engineered metal panel system has its own clips, end closures, terminations
and transitions. Everything from the fasteners used to anchor the concealed clips, through the stiffener
plates, sealants, panels, and closures must be from a single source and UL listed in order to meet UL
wind requirements.
(1) Erection Sequence. Many pre-engineered systems can be installed in one direction only.
For example, from the lower right tier towards the left, followed by the second tier, etc. In addition,
seaming machines vary among systems.
(2) Gutters and Panel Closures. Exterior gutters (where appropriate) must be designed so that
water cannot back up under the panels. When a trapezoidal closure is used it must be adequately sealed
to resist wind driven rain or dislodgment by birds or insects.
(3) Allowance for Thermal Movement. Gable trims, end wall transitions, and ridge assemblies
must be designed to move with the panel.
(4) Underlayment. For watershedding systems decking and underlayment must meet code and
manufacturer requirements. Rubberized (modified bituminous) underlayment is needed along eaves and
in valleys in cold regions where ice damming is likely.
(5) Sealant. Sealant is essential in low-slope metal panel systems. Seam sealant should be
factory installed in the female seam. However, field sealant must be used to supplement the factory
sealant to insure continuity of the waterproofing at clips, endlaps, terminations, and penetrations. Such
details are critical to the integrity of the finished roof.
(6) Alkali Attack. Avoid contact between wet cementitious (alkaline) materials (such as fresh
mortar) with aluminum-coated and zinc-aluminum alloys.
9-7
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