Help Desk Question: Staples and other alternate fasteners
Question: When can I use staples instead of nails? Does APA have a recommendation either way, and if so what size staple is required?
Help Desk Question: Nailhead pull-through adjustment factors
Question: What adjustment factor should be applied to the test values published in APA Technical Topic TT-070: Nailhead Pull-Through Strength of Wood Structural Panels?
2008 APA Publications Index Now Available
The APA Publications Index, Form B300 NN, has been updated. The revised 2008 index provides a complete listing of APA design and construction guides, product guides, builder tips, case histories, industrial publications and other materials available from the Association.
New Engineered Wood Construction Guide
APA just issued the 2007 Engineered Wood Construction Guide, the major reference manual for using engineered wood products in residential and commercial construction.
2006 World Conference on Timber Engineering: Nail Withdrawal and Pull-Through Strength of Panels
A nailed sheathing-to-lumber joint may fail in one of two possible modes when subjected to a load applied along the axis of the fastener: shank withdrawal from the lumber and nailhead pull-through of the sheathing material. Under certain circumstances, such as strong gusts of wind, hurricanes, or seismic activity, shingles or siding may be loosened or detached as nails are withdrawn. Alternatively, these lifting forces may pull roof or wall panels through nailheads. In either circumstance, the integrity of the structure may be severely impacted.
Slant Nail Connections
Several years ago, I received numerous inquiries about the difference between toenails and slant nails. At the time of this inquiry, we developed Technical Topic: Slant Nailing, Form TT-058. This blog entry is intended to briefly discuss the subtle differences between these two nailed applications.
Misconception of nail spacing
ICC ES Legacy Report ER-1952 mentions, “minimum spacing between lines [of nails] is 3/8 inch.”
The purpose of spacing a line of nails every 3/8 inch is to help minimize the potential of wood splitting. We’ve heard some inspectors are interpreting this 3/8 inch distance as the space needed between nail heads. We believe this interpretation is incorrect. The splitting of the framing caused by nails has very little to do with the size of the nail head, but is strongly influenced by the shank diameter of the nail.
Using the species adjustment factor with staples
I recently had a discussion with some fellow engineers about the species adjustment factor in shear wall tables using staples in the International Building Code. When determining the allowable shear for wood structural panel shear walls, IBC Table 2306 footnote (a) requires adjusting the Structural I capacities for staples, using a flat adjustment of 0.82 for most framing species (those with a specific gravity of 0.42 or greater) or 0.65 for others. The footnote also requires adjusting the shear values for the framing with nails and the type of sheathing used based on a formula of (1-(0.5-SG)) but not more than 1.
Stagger nails properly to prevent splitting
Some people get confused about how nails are supposed to be staggered, when there is such a requirement, for example per footnotes e and f of Table 2306.4.1 2003 International Building Code. The figures below demonstrates what staggering is and why it is important. There is no minimum spacing to qualify as stagger, but a good target is about 3/8 inch or more.
Nails vs. screws for sheathing applications
A builder looking for the best possible way to secure sheathing for sub-floors recently asked if screws could be used in place of nails, and whether screws would provide better performance.
APA finds that glue-nailed floor systems perform quite satisfactorily and thus does not have recommendations for fastening structural panels to framing or supports with screws. This is not to say, however, that appropriate structural screws intended for wood assembly should not be used.
Sheathing can stay in re-roofing
If you’re replacing the roofing materials installed over APA Rated Sheathing panels, you don’t need to, as the old saying goes, throw the baby out with the bathwater.
There’s no reason to arbitrarily replace roof-sheathing panels that undergo roofing replacement. Nail holes contribute no appreciable reduction to plywood or OSB panel capacity or performance. As a nail penetrates wood, the point of the nail separates most of the wood fiber instead of boring or breaking through the fiber. The same may be said of small minor panel surface damage. A small amount of fiber may be lost, but this is not considered significant when evaluating the entire panel.
