CEMP-ET
TI 809-53
01 May 1999
8-4.CONSTRUCTION CONSIDERATIONS.
a. General. Wood roof deck products change in dimension with changing moisture content.
Spacing and nailing guidelines for plywood and OSB must be followed in order to avoid buckling. In
general, 3 mm (1/8 in.) spacing is necessary both at panel ends and edges. H-clips may be needed to
achieve this.
b. Pre-roofing Conference. While generic categories exist for asphalt shingles, each type of tile
and proprietary metal shingle will have closures and accessories unique to that type. Mockups may
improve the likelihood that final appearance will be as intended.
c. Shop Drawing Submittals. Submittals have extra significance for historical restoration where
matching the original material is very important. For example, new slate being incorporated into an
existing slate roof should be from the same quarry or manufacturer, if possible (CEGS 07310).
Drawings of transitions between steep roofing and other systems (e.g., membrane roofing) are
necessary.
d. Design Submittal Requirements and Checklist. The steep system should be provided and
warranted by the contractor as a complete system, including valley details, crickets, underlayments,
penetrations, and flashings. The following checklist numbers in parenthesis refer to the CSI
Masterformat number system.
(1) Decking. Install meeting APA recommended spacing (minimum 3 mm [1/8 in.]) at ends
and sides of panels. Fasten at least every 150 mm (6 in.) o.c. at supports and 305 mm (12 in.) at
intermediate supports. Place nails nominally 9.5 mm (3/8 in.) from ends and edges of boards. Verify
that sheathing is spaced and sized properly. When spaced sheathing is used, the deck may be
composed of 25 mm x 100 mm (1 x 4's) for the attachment of wood shingles and 25 mm x 150 mm (1
x 6's) for the attachment of wood shakes. The boards should be spaced on centers equal to the
weather exposure at which the shingles or shakes are specified to be laid. Use solid sheathing for first
900 mm (36 in.).
(2) Underlayment (Sheathing 06113). Minimum of one layer of No. 15 (ASTM D226) asphalt
saturated felt, layered horizontally to the roof slope, minimum headlap 50 mm (2 in.), sidelap minimum
100 mm (4 in.) nailed or stapled sufficiently to hold in place. Use self-adhesive MB or adhesively
laminated underlay at valleys and eaves. For mortar and adhesive-set tile applications, a #30 or #43
organic base sheet (nailed) and mineral surfaced capsheet (mopped) may be used (see Concrete and
Clay Roof Tile Installation Manual, FRSA/NTRMA).
(3) Eave Protection. Use a minimum of one ply No. 30, or two plies of No. 15 felt meeting
ASTM D226, cemented together with lap cement (ASTM D4586 or D2822) or one continuous width of
self-adhesive rubberized asphalt sheet meeting ASTM D1970.
(4) Eave Starter. Verify thickness or number of layers as specified.
(5) Ridge Cover. Confirm if fasteners are long enough to penetrate the deck or if the
adhesive used is applied as specified.
(6) Flashings. Use a minimum dimension of 100 mm (4 in.) up vertical surfaces and 100 mm
(4 in.) out onto the roof deck. Use step-flashing over the end of each course of shingles at all vertical
intersections.
(7) Valleys. Use a minimum of one layer of corrosion resistant sheet metal 600 mm (24 in.)
wide or two layers of roll roofing.
(8) Penetrations. Position penetrations near ridge in snow country.
8-6
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