Originally published: 12/14/2015 03:12 PM  |  Last updated: 01/26/2026 12:05 PM

The following is in response to your inquiry regarding recommendations for gapping wood structural panel (floor/wall/roof) sheathing such as plywood and oriented strand board (OSB).

APA recommends sheathing panels be installed with a minimum 1/8-inch gap on all edges. Gapping of panels is recommended to minimize the risk of panel buckling.

Buckling of wood structural panel sheathing occasionally results when high moisture conditions cause the panels to expand. Although structural properties are not affected by moisture induced buckling, the waviness may affect appearance and cause concerns about serviceability.

Gapping of ends and edges of roof sheathing panels permits the natural expansion that results from moisture acclimation to humidity or wetting during construction. The panel gap is likely to close naturally as a result of panel acclimation. Absence of a panel gap during later inspection of the roof deck may be indicative of gap closure, rather than absence of a gap during installation. In fact, this is the intent of providing the gap.

While it is a recommendation to install the wood structural panels with a 1/8-inch gap, gapping is not addressed in model building codes since it is not possible to verify the gapping after a period of time and has no effect on the structural capacity of the panels.

In dry climates, it may be possible to butt panels to a light contact based upon satisfactory past field experience, but the contractor is at risk if a buckling problem develops.

In any case, if the (floor/wall/roof deck) flatness is acceptable after moisture acclimation, APA would generally recommend that (construction/roofing) proceed. (2003 WAB/SCZ)

Maximum Gap:

From APA’s perspective there is no maximum recommended gap or space at panel edges and ends. The important factor is that adequate edge distance is provided for fasteners in both the wood structural panels and the framing.

Shear wall tests are performed using 2x framing, the recommended 1/8-inch panel spacing, panel fastener edge distance of 3/8-inch and 5/16-inch for the framing.

If more than 1/8 inch panel edge spacing is provided, or more than 3/8 inch fastener edge distance is used, a wider framing member may be required at panel edge locations to provide adequate framing edge distance for fasteners.

APA Engineered Wood Construction Guide, Form No. E30, states: "Supported Panel shall occur approximately along the centerline of framing with a minimum bearing of 1/2-inch." This further restricts allowable panel edge gap.

Gap size is of no significance to panel capacity for loads normal to the face, lateral loads or other loads. Performance of products applied over wood structural panels may be impacted by excessive gap, e.g. roofing or floor covering materials. Check with covering material manufacturers for maximum gap limits when appropriate. (2006 MK)

Why Gap?

A builder may have been omitting the edge and end gaps for years without any observed problems. Why start now? Why do I have a problem now?

Due to the manufacturing process, panels may be very low in moisture content when produced (2-3%).

Eventually the moisture content of the panels will reach an equilibrium of around 8-14%. The actual moisture content will depend on the geographical area and the time of year. The result of corresponding expansion is a build up of internal stresses within the panels, or buckling.

Historically panels were produced at the highest rates possible by mills. Sales were made from warehouse inventories. As a result, high inventories of panels often caused long delays between the time of production and the time of use. This delay allowed the panels to reach a balanced moisture content much closer to ambient before reaching the market.

In today’s market panels are manufactured on a JIT basis. They aren’t produced until a sale has been made. This results in panels being shipped to distributors and dealers as soon as they are produced. It is not uncommon for panels to reach a job site still hot off the presses, "Hot Stacked." As a result the panels have no time to absorb moisture and expand.

APA recommends leaving 1/8 space at all sheathing and Sturd-I-Floor edge and end joints, including tongue-and-groove joints.

SPACING HINTS:
1. Use a 10d box nail as a spacer to gauge a 1/8 inch gap.
2. For roof sheathing spacer-type panel edge clips are available from some manufacturers.
3. If necessary, trim panel ends to center on framing.

(2001 MK)

Original categories: Roof, Floor, Wall