APA recommends sheathing panels be installed with a minimum 1/8-inch gap on all edges unless the panel manufacturer indicates otherwise. Gapping of panels is recommended to minimize the risk of panel buckling (a serviceability issue) when panels are exposed to moisture during construction or acclimatize after installation.

Panels will increase in length and width as they absorb moisture from humid air or from rain. From their initial mill-dry state, panels may expand as they reach their equilibrium moisture content. If they are installed without room to expand, panels may buckle.

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. Panels installed with the recommended gap may expand due to moisture until there is no gap visible. In fact, this is the intent of providing the gap.

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.

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

SPACING HINTS:
1. Use a 10d box nail as a spacer to gauge a 1/8 inch gap.
2. If necessary, trim panel ends to center on framing.

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. If not gapped the natural expansion will build up axial compression stresses within the panel which can lead to panel buckling.

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?

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. However, in modern markets panels are often manufactured on a just in time basis. They aren’t produced until a sale has been made. This new situation is resulting 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.