HomeMy WebLinkAboutInfo (Panel Spacing Recommendations) - 08/07/2003 ILIcliti p i E EVE
REC o i
iMENTire 2
r,O MUNITY DEVELOPMENT
Spacing, Storage and Handling of Panels
Panel Spacing Recommendations
Spacing of wood -based panels during installation to allow for expansion caused by excessive
moisture has been a recommendation of the panel industry for more than two decades. In fact, an
early national code report of the American Plywood Association included requirements that square -
edged and tongue- and - groove joints be spaced (NRB -108, August 1978), although APA's current.
NER report makes no specific reference to panel spacing requirements or recommendations. While
the PFS Research Foundation has historically not required that structural wood -based panels be
spaced, it has endorsed minimum panel spacing recommendations to reduce the frequency of
buckling and other problems associated with excessive panel expansion.
Wood -based panels, like other wood products, expand when their moisture content (MC) increases.
Panels bonded with exterior adhesive are shipped from the mill with an MC in the range of 2 to 6
percent. Over time, panels will equilibrate to the local environment, which can range from as low as
4.0 percent in Las Vegas in the summer to over 17 percent in cities in the Pacific Northwest in the
winter (Table 12 -1 of the Wood Handbook, USDA, 1999). Because most of North America has as
average equilibrium MC above the 2 to 6 percent range, panels will usually expand after they leave
the mill.
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b \ - til'iv For this rea on, and even though spacing is not addressed in the major model building codep, the
PFS Research Foundation has traditionally recommended that panels be spaced as shown in the
above diagram, unless specific recommendations or requirements are included by the manufacturer.
Grade stamps that manufacturers stamp on panels highlight this fact and often contain the note
"Sized For Spacing," meaning that panels are cut to be less than nominal dimensions, usually 1/8
inch short in both width and length. A sample of a "Sized For Spacing" note in a gradestamp is
included on the following page.
(cont. on back)
For additional information, contact PFS Research Foundation at 1- 608 - 221 -3361 TT/Space, 2 1027/99