- Q. Our local energy utility recommends framing exterior walls with a single top plate to cut down thermal conduction. We follow the CABO code when we do this, making sure we line up trusses and/or joists directly over the studs. We splice the top plate joints with Simpson TP37 straps for 2x4 walls and TP47s for 2x6 walls, using three Teco nails on each side of the splice (the code actually calls for three 8d nails on each side). Even though the single top plate is approved, I still get comments from subs and carpenters that it doesn’t look strong enough. I wonder, from an engineering standpoint, whether this method is as strong as using the traditional double top plate?
A. Robert Bouchet responds: Actually, a double top plate, correctly lapped and nailed, is considerably stronger than a single plate and a TP connector. For example, one of the forces acting on the top plate is the lateral force from wind or an earthquake. As the wall racks from this force, tension develops at the splices in a double top plate. The CABO code allows you to place top plate splices a minimum of 4 feet apart (see illustration), and requires two 16d nails at the splice and another 16d nail every 24 inches. So at the very least, you would have four 16d nails between splice points resisting this tension force. Compare that to the three 8d nails on each side of the TP connector plate and there’s no question which is stronger.
So far I’ve talked only about tension. The bending and shear strength of the double top plate would also greatly exceed the strength of the single plate. It should be noted, however, that the added strength of a double plate may not be necessary for a particular structure. If in doubt, check with your code inspector or an engineer.
Be careful using terms like "Teco" and penny-weights for nails, especially when installing load-rated metal connectors: The performance of a specific connector depends on using nails of the proper length and diameter.
Robert Bouchet is an engineer with the Simpson Strong-Tie Co. in Pleasanton, Calif.