When carpenters from other parts of the country come by one of our jobsites, one of the first questions they ask is, "What's that nailed to the ceiling joists?" When I answer, "Strapping," they then ask, "What is that for?"
The first few times I got these questions, I figured that these guys must not be real carpenters: How could they not know what strapping is? What I now know is that the Northeast is one of the few areas in the country where we strap our ceilings as a matter of course for every house we frame, regardless of the floor framing material. Strapping serves many purposes both for us as framers, as well as for many of the subs who follow.
Attaching the drywall
My understanding is that installing strapping originated from the need to create a flat surface for attaching the ceiling to the uneven hand-hewn timbers once used as structural framing members. Carpenters shimmed the strapping down to the lowest point in the room and then attached the finish material. While we no longer need to shim the strapping to achieve a relatively flat ceiling, the board hangers that follow behind us appreciate a full 2 1/2 inches to attach the board to rather than the 1 1/2 inches provided by dimensional lumber. We can also easily add nailing along walls that run parallel to our strapping.
Making the subs happy
The trades that work in this area always appreciate strapping. Electricians can use the 3/4-inch space to make long runs perpendicular to the floor joists without having to drill holes. Strapping in existing ceilings also makes snaking wires much easier. Plumbers can also save labor by running their 1/2-inch PEX tubing below the joists; and they can use the strapping to support waste and vent pipes at the required pitch.
If a room is being trimmed out with crown molding, we often add multiple rows of strapping along the walls for the finish carpenters. Strapping can also provide extra nailing for coffered ceiling details.
Strapping makes it easier for us to install interior partitions, too. Rather than adding attachment blocks between the joists above the walls, we just add a few lengths of strapping, running them one bay longer than the wall. This gives the framer and the board hanger plenty of nailing to which they can attach the walls and drywall. Instead of an upper wall plate, we use a length of strapping to make up the final 3/4 inch of wall height. The thinner "top plate" also makes it easier to raise the partitions into place.
Adding rigidity to the floors
Strapping can also add measurable strength to floor and ceiling systems. In two recent situations, engineers took our strapping into consideration to make a framing situation acceptable.
In the first, we used 11 7/8-inch I-joists to frame a large 20-by-28-foot living room. The room had very little actual floor weight, a situation that often leads to unacceptable levels of floor vibration. With no finished ceiling in the basement below the living room, the long spans of joists can twist when loaded. The torsional flutter that is created increases a certain amount of perceived vibration in the floor. Strapping attached to the basement ceiling eliminated joist deflection and brought vibration to an acceptable level.
The second situation we experienced was a hip roof over an unfinished attic space. The builder didn't want to sheath the attic floor area, which raised concerns about racking for the engineer. When I told him we would be strapping the ceiling, he said that the strapping would perform the same function as the sheathing would have.
Installing strapping
We strap the ceilings after all ceiling and bearing-wall framing is finished. Working in teams of two, each carpenter begins by laying out an end of the room at 16 inches on-center. When the entire room is laid out, we snap chalk lines on the ceiling to ensure a straight and clean installation.
After snapping all of our lines, we lean lengths of strapping against the top plate at one end of the room. One carpenter then picks up a piece, places it on the line, and tacks it to a joist roughly in the middle of the length of strapping. He moves across the room tacking all the strips in place, then nails the starting end of each piece.
At the same time, his workmate saws the pieces to length in place, staggering the lengths between joists. For us, this method is faster than measuring and pre-cutting the pieces. After the cut ends are nailed up, the carpenters move across the room adding full lengths of strapping. Once all of the full-length pieces are tacked in place, one carpenter cuts finish pieces to length, while his partner nails off the entire roomwith the nail gun.
After the room is strapped, we nail in any additional pieces as needed at parallel walls or beams. We lay out partitions on the floor and shoot those locations on the ceiling with a laser. Then we add additional strapping at those locations.
Once you've mastered the installation process, strapping ceilings goes very quickly and easily. Because strapping is included in every framing job we do, it's tough to put an exact price on the additional material and labor, but the cost is not significant.
Matthew Anderson owns Anderson Framing & Remodeling Co., in East Sandwich, Mass.
