Q: My last trip to the hardware store left me confused. I just wanted a box of nails. But the shelves were filled with all variety of nails with any number of names: Common, Box, Cooler, Ring Shank, Cement Coated, Drywall, etc. Why so many names? Isn't a nail a nail?
A: Giving special names to particular sizes and styles of nails was a convenience for the trades. It was meant to assist them in obtaining the proper nails for their particular work. And for some trades, the names of the nails have outlasted their uses. This is where the typical project can run into difficulty.
Engineers and Architects generally specify "common" nails on their project plans. We do this because the allowable strengths of wood-to-wood connections and plywood diaphragms given in the building code are based on the use of common nails. A typical notation would look like: "10d's at 12" o.c."... which would indicate the need for "ten pennyweight (common) nails spaced at twelve inches on center". A "pennyweight" is a reference to the cost of 1000 of these nails in old British currency. Standing in the store, you observed several boxes with a "10d" designation on them followed by one or more words. They are not all equivalent.
A nail's strength is based on its length and its diameter. Given the proper length, the nail will be driven far enough into the supporting member that it will be capable of developing its maximum allowable lateral strength. The strength of a properly placed nail is also dependent on its diameter as this affects the quantity of wood fibers that can bear against its surface. The "wider" the nail (greater diameter), the more wood fibers can bear, the stronger the connection. The following is a table of various nails, their lengths and diameters.
For comparison purposes, we will imagine the nailing requirements of a typical plywood shear wall where the notes called for "10d's at 6" o.c.". An error begins when the contractor misses the sentence in the general notes calling for "Common" nails and picks up the first box of nails labelled "10d" or receives a fifty pound box of 10d nails from his supplier with the framing lumber and asks no further questions. If those 10d's were actually "Box" nails, what would this do to the strength of the finished construction?
Not encouraging, is it? The same decrease in strength holds true for floor and roof diaphragms, plate laps, toenails, etc. if nailed with the smaller diameter version of a "d" (pennyweight) designation nail.
What you can do:
1. It's a simple task to visit the job site and pick up samples of the nails your contractor is using. Measure their diameters. Compare what you are getting with the tables above and with the project plans. Bring any discrepancies to the attention of your design professional and to the contractor. Stand firm, do not be bluffed or dismissed. Expect to receive either documentation stating that the connection(s) will function adequately using the smaller nails or expect the corrections to be documented and installed at no additional cost to you.
2. Have the professional you are working with emphasize the need for common nails with a separate note on the framing plan(s). A sentence or two of highlighted or bold text should do.
Scott McVicker, S.E.