Page
20
Unirac Code-Compliant Installation Manual
SunFrame
R
1411 Broadway Boulevard NE
Albuquerque NM 87102-1545 USA
Material planning for rails and cap strips
Preplanning material use for your particular array can prevent
structural or aesthetic problems, particularly those caused by
very short lengths of rail or cap strip. This example illustrates
one approach.
Structural requirements for rails are detailed in “Footing
and splicing requirements” (p .18) . Structurally, cap strips
require:
• A screw in every prepunched hole (which occur
every 8 inches, beginning 4 inches from the ends of
the rails) .
• One screw 4 inches or less from the each end
of every rail segment . Wherever there is no
prepunched hole within 4 inches of an end of a
segment, drill a
1/4
-inch hole 2 inches from the end
of the segment and install a cap strip screw . (In
most cases, you can avoid this situation with good
material planning .)
Structural requirements always take precedence, but usually
good planning can also achieve both material conservation
and superior aesthetics . This example conserves material
and achieves two specific aesthetic goals:
• Cap strip screws must align across the rails .
• End screws must be equidistant from both sides of
the array .
The example assumes an array of three rows, each holding
five modules 41 inches wide . Thus, four 205-inch rail
assemblies and cap strip assemblies need to be cut and
spliced from 192-inch sections of rail and cap strip . The
example illustrates one means of doing so, without violating
structural requirements or aesthetic goals .
Rail segments come from five 192-inch lengths, lettered A
thru E . Rail A, for example, is cut into two 96-inch segments,
with one segment spliced into each of the first two rails .
Similarly, five 192-inch cap strips are designated V through Z .
All cap strip segments are cut at the midpoint between
prepunched screw holes . For each rail, start with the cap
strip segment that crosses the array center line, and position
over the center line so that the appropriate holes are spaced
equally on either side .
Position each cap strip onto its rail and mark its trim point .
Remove and trim before final mounting .
Preliminary footing and splice positions must be
checked against structural requirements in “Footing
and splicing requirements” (p.18). In this example,
the center of the array is offset 2 inches from the center
rafter. This prevents rail splices BD (3rd rail) and CE
(4th rail) from falling too close to the center of the spans
between footings (Requirement 3, p. 18). Because foot-
ings are not visible from ground level, there is negligible
aesthetic loss.
A 96″
B 109″
A 96″
B 83″
C 83″
C 109″
D 122″
E 122″
Array center line
V 112″
W 112″
W 80″
V 80″
X 96″
Y 128″
X 96″
Z 128″
Usable remainder: D, 70″; E, 70″; Y, 64″; Z, 64″
4th cap strip
1st rail
3rd cap strip
2nd rail
2nd cap strip
3rd rail
1st cap strip
4th rail
Trim line (array edge)
Trim line (array edge)
