Georgia-Pacific APA Engineered Wood Construction Guide - Floors - Manual (Page 13)

Floor Construction
ENGINEERED WOOD CONSTRUCTION GUIDE ■ FORM NO. E30V ■ © 2011 APA – THE ENGINEERED WOOD ASSOCIATION ■ WWW.APAWOOD.ORG 40
Always protect plywood Underlayment against physical damage or water prior to application. Panels should, however, be
allowed to equalize to atmospheric condi tions by standing individual panels on edge for several days before installation.
Install plywood Underlayment, smooth side up, immediately before laying the finish floor. For maximum stiffness,
place face grain across supports. Edge joints of underlayment panels should be offset by at least 2 inches from joints
of subfloor panels. Underlayment end joints should be offset from subfloor end joints by at least one joist spacing, and
Underlayment end joints should be offset from floor joists by 2 inches, so that nails miss the framing (to minimize the
chance of nail pops).
Begin fastening at one edge next to a preceding panel. Assuring that the panel is uniformly flat, continue by fully fas-
tening toward opposite edge. If power-driven fasteners are used, foot pressure should be applied near the fastener to
ensure firm contact between the Underlayment and subfloor. Make sure fasteners are flush with, or just slightly below,
surface of Under layment just prior to installation of resilient floor coverings such as tile, or sheet vinyl. (See
Table 14
for Underlayment recommenda tions for thin flooring products.) Fill and thoroughly sand edge joints. (This step may
not be necessary under some carpet and structural flooring products – check recommendations of flooring manufac-
turer.) Fill any other damaged or open areas, such as splits, and sand all surface roughness. (Ensure fill compound is
fully cured before sanding because it may continue to expand as it cures.)
The plywood Underlayment needed to bridge an uneven floor will depend on roughness and loads applied. Although a
minimum 11/32 Performance Category is recom mended, 1/4 Performance Category plywood Underlay ment may also
be acceptable over smooth subfloors, especially in remodeling work. (See
Table 14 .)
Where floors may be subject to temporary moisture, use panels with exterior glue (Exposure 1) or APA C-C PLUGGED
Exterior. APA C-D PLUGGED is not an adequate substitute for Underlayment grade since it does not have equivalent
face veneer puncture resistance.
Hardwood Flooring Over APA Panel Subfloors
APA panel subfloor spans for 3/4-inch hardwood strip flooring are limited to maximum spacing of floor framing listed in
Table 12. For improved stiffness, and to help eliminate floor squeaks when hardwood flooring is installed, spans reduced
from the maximum are recommended by the National Wood Floor Association (NWFA)*. NWFA also recommends
the use of minimum 23/32 Performance Category OSB or 19/32 Performance Category plywood as a subfloor material.
Because hardwood flooring is sensitive to moisture, make sure subflooring panels are dry before hardwood is installed.
Use a moisture meter to measure the moisture content of the subfloor. Do not install hardwood unless subfloor mois-
ture level is within a range consistent with the hardwood manufacturer’s recommendations. If the home is built over a
crawl space, make sure the crawl space is dry and well-drained. A 6-mil polyethylene vapor retarder should be installed
on the ground in the crawl space.
Follow the recommendations of the National Wood Flooring Association (NWFA) for the hardwood flooring product being
used and its storage and handling, and for acclimatizing the hardwood prior to installation on the subflooring. Also see
APA
Technical Note: Performance Rated Panel Subfloors under Hardwood Flooring, Form R280 .
Ceramic Tile Over APA Plywood Floors
Recommendations for several plywood floor systems suitable for application of ceramic tile are given in Table 15, based
on specifications of the Tile Coun cil of North America (TCNA).** In designing such a floor system, expected live loads,
concentrated loads, impact loads and dead loads, including weight of the tile and setting bed, need to be considered.
For additional details and assemblies, see Technical Topic: Ceramic Tile Over Wood Struc tural Panel Floors, Form TT-006 , at
www.apawood.org .
* National Wood Flooring Association , 111 Chesterfield Industrial Boulevard, Chesterfield, Missouri 63005; Phone (800) 422-4556 (USA),
(800) 848-8821 (Canada).
** Tile Council of North America, Inc. , 100 Clemson Research Blvd., Anderson, South Carolina 29625; Phone (864) 646-8453.