Installation Guide

Floor Construction
ENGINEERED WOOD CONSTRUCTION GUIDE
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FORM NO. E30V
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© 2011 APA – THE ENGINEERED WOOD ASSOCIATION
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WWW.APAWOOD.ORG
39
TABLE 14
APA PLYWOOD UNDERLAYMENT
(a)
Plywood Grades
(b)
Application
Minimum
Plywood
Performance
Category
Fastener Size
and Type
(c)
Maximum Fastener
Spacing (in.)
(d)
Panel
Edges
(e)
Intermediate
APA UNDERLAYMENT APA
C-C Plugged EXT APA RATED
STURD-I-FLOOR (19/32 or
larger Performance Category)
Over smooth subfloor 1/4 3d x 1-1/4-in. ring-
or screw-shank nails
min. 12-1/2 gage
(0.099 in.) shank dia.
(f)
3 6 each way
Over lumber subfloor
or uneven surfaces
11/32 6 8 each way
(a) For underlayment recommendations under ceramic tile, refer to
Table 15.
(b) In areas to be finished with resilient floor coverings such as tile or
sheet vinyl, or with fully adhered carpet, specify Under layment,
C-C Plugged or veneer-faced STURD-I-FLOOR with “sanded face.”
Underlayment A-C, Underlayment B-C, Marine EXT or sanded
plywood grades marked “Plugged Crossbands Under Face,” “Plugged
Crossbands (or Core),” “Plugged Inner Plies” or “Meets Under layment
Requirements” may also be used under resilient floor coverings.
(c) See Table 5, page 14, for nail dimensions.
(d) Fasteners for 5-ply plywood underlayment panels and for
panels with a Performance Category greater than 1/2 may be
spaced 6 inches on center at edges and 12 inches each way
intermediate.
(e) Fasten panels 3/8" from panel edges.
(f) Use 4d x 1-1/2" ring- or screw-shank nails, minimum 12-1/2
gage (0.099") shank diameter, for underlayment panels with a
Performance Category of 19/32 to 3/4.
Underlayment grades of plywood have a solid, touch-sanded surface for direct application of carpet and pad. For
areas to be covered with resilient floor covering, specify panels with “sanded face,” or certain other grades as noted in
Table 14. Special inner-ply construction of Under layment resists dents and punctures from concentrated loads. Applied
as recom mended, plywood Underlayment is also dimensionally stable and eliminates excessive swelling and subse-
quent buckling or humps around nails.
Joint stagger optional
for subfloor panels
Spacing
of 1/32" recom-
mended at under-
layment butt joints
APA RATED SHEATHING
or board subflooring (subflooring
must be dry before laying underlayment)
No blocking required
if underlayment edge joints
are offset from subfloor
joints or if tongue and
grooved (T&G) subfloor is used
Resilient tile or sheet
flooring, carpet or
nonstructural flooring
APA plywood underlayment
(see Table 14 for underlayment
recommendations for thin
flooring products)
FIGURE 6
INSTALLATION OF APA PLYWOOD UNDERLAYMENT
Subfloor and
underlayment
panels oriented
with strength
(long) axis
across
supports
Stagger end joints by at least one joist spacing
in underlayment panels (optional under carpet
and pad) for maximum stiffness and strength
Min. 2" offset from
subfloor edge joints