- 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,