Article #124 - Single Top Plates - Code Notes

A single top plate is allowed under the International Residential Code (IRC), but it is an uncommon construction practice. Standard practice for exterior and interior wall framing is to use a double top plate to connect wall segments and to support framing above the plates.

Eliminating unnecessary wood framing within walls can increase the thermal efficiency of the wall system. Less framing allows more insulation to be installed and also eliminates hot and cold spots (from thermal bridging through the frame) within the wall system.

The single top plates must be adequately tied at joints, corners, and intersecting walls by at least a 3-inch x 6-inch, 0.036 inch-thick galvanized steel plate that is nailed to each wall or wall segment by six 8d nails on each wall segment. Rafters or joists bearing on a single top plate must be within 1 inch of center over the studs below. The top plate may be omitted over lintels that are similarly tied to adjacent wall sections with steel plates. The single top plate may not be appropriate in regions with high wind loads or seismic regions when the double top plate may be needed for structural requirements.

Interior, nonbearing walls may be 2-inch x 3-inch studs spaced 24 inches (610 mm) on center. Or, if not part of a braced wall line (a series of braced wall panels), 2-inch x 4-inch flat studs, 16 inches on center may be used. Interior, nonbearing walls must be capped with at least a single top plate and be fireblocked.

Plan Review

1. Verify that the wall framing details call out a single top plate and also specify the 3-inch x 6-inch, 0.036 inch-thick galvanized steel plate to be installed at each corner and wall segment. Also verify that the nailing exception is specified on the building plans.
2. Verify that the spacing for the roof framing is identical to that of the wall framing. For example, the roof framing must be spaced at 24 inches on center if the wall framing is also spaced at 24 inches on center. The rafter/roof trusses must be within 1 inch of being centered above the wall studs.
3. If the wall system supports a floor, verify that the floor joist spacing is identical with the wall stud spacing.
4. Confirm that the single plate will not be exposed to high wind load or high seismic areas. Double top plates are required in these areas for lateral loading.

Field Inspection

1. Verify that the top plate is fastened to the studs (two 16d nails).
2. Verify that a 3-inch x 6-inch, 0.036 inch-thick galvanized steel plate is installed at each corner and wall segment and that six 8d nails are used to attach each side of the plate to the corner or wall segment.
3. Verify that the rafters or trusses used in the roof framing are within one inch of the center of each of the studs below.
4. Verify that the floor joists supported by the studs are within one inch of the center of the studs below.

Code Citations*