Editor’s Note: This article was originally published on the Wick Buildings blog. It was published, with permission, in the November edition of Frame Building News magazine.
To guarantee quality in your post-frame construction, the devil is in the details. The use of nails vs. screws in your pole barn building is a perfect example. Knowing when, where, and why each fastener should be used is yet another step towards helping you get the most bang for your buck.
The use of nails vs. screws typically comes down to one overriding issue: money. But that’s not necessarily the best approach to having a building your customer will be satisfied with for years to come.
Screws, without a doubt, provide a more secure connection. Nails, however, are generally less expensive to use. In actuality though, screws and nails both have their place. In this article, we’ll describe the best application for each.
Wood-to-Wood: Using Nails “Under” the Steel
Whether you’re applying nails or screws, the goal is to provide enough shear strength to support wind and snow loads.
Nails are best used in three specific areas of your post-frame building, all of which are essentially under the steel that will ultimately wrap around the structure. (We’ll get to that steel in the section on screws.)
Three Areas Well-Suited for Nails
1. Girts to Columns. Girts are horizontal lumber components that connect columns. Note that they’re placed on the outside of the columns. The exterior side-wall steel is eventually fastened to the girts. Girts should be attached with nails of the appropriate size and quantity.
2. Purlins to Trusses. Much like how the girts form the framework for the steel on the walls, purlins do the same on the trusses, where the roof steel is attached. Same drill here as the girts: Use the correct size and right amount of nails to secure the purlins to the trusses.
3. Bracing. During construction, the bracing keeps the
building frame plumb and level prior to structural sheathing. Permanent bracing stiffens the structure and helps the structure withstand wind and snow loads.
Bracing is actually used to connect all the components we’ve just mentioned—columns, girts, purlins, and trusses. Properly sized and placed nails can be used effectively for the bracing.
Bonus Tips on Using Nails
Ring-shank nails. A ring-shank nail will provide even more strength than typical nails. The circular pattern embedded in the nail locks into the wood fiber when it’s driven into place. Wick uses only ring-shank nails.
Galvanized nails. Much like builders can cut corners on the use of nails versus screws, another way to shave money is to skimp on the quality of the nails. But you don’t want to do that.
For example, in areas subject to corrosion, like buried columns, splash planks, and anywhere a nail is exposed to weather, galvanized nails should be used.
Using a less expensive nail shouldn’t be a financial decision. It should be based first and foremost on the requirements dictated by the engineers designing the building, who can specify the type of strength you need.
Steel-to-Wood: Securing Your Steel Structure with Screws
Always use screws to attach your exterior steel siding to a structure. Compared to nails, the standard screws that we use generate significant pull-out resistance: 122% compared to ring shank and 352% compared to smooth shank.
Just think of it this way: When fasteners begin pulling out, structural movement occurs. Why is this so critical on the steel that encases your building? Here are two big reasons:
1. It’s your frontline defense. The steel that wraps your post-frame structure is your outermost material. It’s the frontline against the elements. Over time, moisture, temperature, wind, and snow loads can cause your building to move. Screws help combat that movement.
2. It forms a strong shell. That steel not only provides a barrier to the elements; it also ties the structure together and gives it strength. When the entire shell is fastened with maximum resistance thanks to screws, your building will be stronger and have a longer lifespan.
Basic Guidelines on Screws
Greater resistance for longer screws. The longer the screw, the more likely it is to control contraction and expansion of steel. Due to the length of the panels, this is especially critical when attaching roof steel.
Wick uses 1½” screws to attach the steel panels to the roof. These screws provide an uplift load resistance 56.5% greater versus 1” screws. We’re always cautious of diminishing returns, but these numbers make our decisions easy.
Screwing in the flat versus the rib. Some builders will install screws on top and through the major rib of your steel siding, versus in the flat. They’ll use a 2” screw and install it on the top of the rib.
Unfortunately, the uplift resistance is lower, because only an inch of the screw goes into the wood (see visual below). This also makes the panel more susceptible to moving when wind and snow exert stresses on your building, and when the steel panel expands and contracts with heat and cold.
By screwing in the pan (the lower part of the steel), you gain 56% greater uplift resistance, as 1½” of the screw sinks into the wood. You also get less movement due to wind, snow and temperature stresses.
The argument against using the screw in the flat or pan, especially on the roofline, is that water runs through those channels, and has greater potential for leaking at the screw.
However, that’s a potential problem easily overcome by using the appropriate screw with an integral washer head design, which reduces overdriving and ensures a weathertight seal.
Use Data, Not Dollars, to Make Your Decision
As we’ve noted, both screws and nails have their place. Just don’t forget that this really should be an engineering decision first, not an economic one.
A qualified engineer can use data to determine what’s best and ultimately make the nail vs. screw decision an easy choice.
The whole nails or screws topic is really just the tip of the iceberg when it comes to the decisions you’ll need to make when building a pole barn. It’s no small undertaking, and everyone has different capabilities, timelines, and budgets. Just know that you don’t have to go it alone. FBN
