Tag Archives: osb under steel

AdvanTech®

AdvanTech®

Christina reached out to me on social networking and asked:

“Hello, always look forward to your advice and I ran across something I didn’t find on the Hansen website. AdvanTech flooring as an alternative to OSB or plywood. Thoughts?”

While I have successfully utilized AdvanTech subflooring myself, rather than reinventing a wheel, today’s expert opinion comes from Matt Risinger (you may recognize him from www.buildshownetwork.com).

Matt writes:

When I started out in construction, I was working for a production builder. For many years, like most builders of that era, we used OSB (oriented strand board) subfloor — typically a 3/4-inch tongue and groove panel. There was no real choice in OSB then. It was whatever was available from the lumber supplier and we didn’t think a whole lot about it. We used a conventional construction adhesive and nailed off the floor, as that was the fastest method. But we had all kinds of squeaks on the houses we built. I thought that making the transition to screwing down the subfloor would be the answer to my squeak problems, but this didn’t help all that much. We still had frequent callbacks for squeaks. We also had a fair amount of edge swelling — an inevitable result of rain during the framing stage before we got the house dried in. That was a pain, too, because the swelling resulted in a wavy, bumpy floor that contributed to the squeak problems. Floor squeaks are the result of wood movement. Either a nail comes loose, or a screw shears off and you have up-and-down movement, or the edges swell and cause gaps beneath the underlayment that allow for creaks. Frequent callbacks did not do a lot for either the builder’s reputation or for the bottom line.

When I was working for a production builder, I didn’t really have much say in the purchase of materials, so I wasn’t able to change to a different subflooring product. Honestly, at that time, I did not really know there were other options. But when I started building custom homes about 12 years ago, one of the first changes I made was the switch to plywood. It was 1-1/8-inch plywood we should have glued to framing but just nailed it. This provided a nice stiff floor and eliminated my squeak issues. However, on one of my very first houses using plywood, we had a giant downpour during construction when the frame was open. This resulted in a ton of edge swell. Being a custom-built house, I had to fix it by sanding the edges and flattening the floor. The whole time the job was on pause for this to happen, all I could think was “OK, I love that I have eliminated squeaks. I love that I have a stronger, stiffer floor. But, man, this edge swell is a pain.” (And I hadn’t budgeted for the sanding either.)

I was looking for something better, but I thought “OSB? I’ve used that before and had problems. I’m not going back to that!” It was around that time, maybe 10 years ago that someone suggested I try AdvanTech subflooring.

I was soon to learn that there’s a big difference between AdvanTech panels and other subflooring options. Commodity OSB uses glues and a process that permits the panel to soak up moisture. Most subfloor-grade plywood uses similar glues between the laminators. While plywood gives you a more consistent panel, it is still prone to wicking moisture.

Plywood and OSB manufacturers try to improve this by sealing the panel edges, but the sealant, whether it is a wax or a paint, tends to get scuffed off. Think about how often panels get dragged on their edges across a truck bed or across the floor deck in the process of installing them.

Two things really distinguish how AdvanTech panels are made that contribute to their high performance over commodity OSB: resin technology and manufacturing precision. AdvanTech panels use an advanced liquid resin that coats flakes during the manufacturing process to make sure the panel is thoroughly protected. A lot of engineering and quality control goes into how the strands in AdvanTech panels are oriented and sized within the multiple layers to create a woven matrix of fibers that achieves the right balance of stiffness and dimensional stability. Commodity OSB is also set up in layers but can have larger variations in strand size and orientation within the layers and may use a different kind of resin that does not necessarily have the same moisture resistance. The AdvanTech subflooring manufacturing process also has a high level of precision to make sure the wood strands are the optimal thickness and dimension for a more stable panel. During manufacturing at AdvanTech panel mills, there are extensive quality control checks along the whole panel production process so that only the very best final boards earn the AdvanTech brand mark.

Once I made the switch to AdvanTech subflooring, I had zero edge swell, even with heavy rains during construction.

I’ve not had a single squeak and never had to sand edges down. That has been a huge change for me. I opt for the 1-1/8-inch panel on most of my projects because I want zero bounce in the floor. Certainly, I spend a little more on this subfloor than I have in the past. However, the elimination of problems makes it totally worth it. As with most materials choices, it’s never just about initial cost. Think about it: Not having to pay the unexpected costs of sanding, which interrupts the flow of the project, is one thing. But if I had to fix a squeak after the owners have taken possession and are living in the home, that is a nightmare. My business is based on an expectation of quality. Having no callbacks — having a much stronger, squeak-free floor — has made all the difference in being able to build a solid reputation for high-performing homes.

Having now gained some insight into AdvanTech’s benefits, it does come with some added investment. As compared to OSB subflooring AdvanTech will add roughly 75 to 90 cents per square foot of surface area (comparing nominal ¾” thickness products at current market prices).

OSB Under Steel Roofing On Pole Buildings

Almost anything can be sold as a benefit…

Most post frame buildings are sold to the unsuspecting or ill-informed client based upon a set of features. These features may or may not have an actual benefit to the long term performance of the building. What is most unique is – the sales person often has no clue as to whether the feature has a benefit or not! They are just selling it as if it actually was beneficial.

Case in point – one of our recent clients in Colorado has hired a building contractor to erect his building. This particular contractor happens to admit to sheathing over 90 percent of all of the post frame buildings he has put up in 7/16” OSB (Oriented Strand Board) beneath the steel roofing and siding. While this may sound great and wonderful (not to mention expensive), does it truly offer a benefit to the client?

Think of roll formed steel roofing and siding as performing like a very strong, very thin plywood and you will have a better grasp of how it performs. The only reason to put OSB on a roof would be in the case of a very narrow, very long, very tall building with high wind loads – ones which would exceed the wind shear carrying capacity of the steel. This case is most certainly the exception to the general rule and happens in far less than 5% of all post frame buildings. Even in those cases, the OSB is only effective in the bays closest to the endwalls, where shear forces are greatest. As for the walls – on endwalls with a significant number of openings, it becomes necessary to reinforce the steel siding with OSB (generally at the corners). Outside of this, there would not be an economically practical reason to sheet the walls with OSB.

Let’s look at some numbers…

From the 2012 IBC (International Building Code) Table 2304.6.1 – over framing spaced 24 inches on center, 7/16” OSB fastened with 8d common nails six inches on center at the edges and in the field will support a maximum design wind speed (Vult) of 110 mph (miles per hour) in Exposure B or 90 mph in Exposure C. Table 2304.7(3) gives the 7/16” OSB the ability to carry a roof live load of 40 psf (pounds per square foot) when spanning the same 24 inches.

The 2009 IBC in Table 2306.2.1(1) gives the shear value for 7/16” OSB with 8d nails six inches on center as 230 pounds per foot for a Case 1 layup (long side of the panel towards the load, and joints staggered by four feet) in Douglas Fir, with an 18% reduction for use with SPF (Spruce-Pine-Fir) or Hem-Fir.

Compare this to 29 gauge steel. From information provided by Fabral (https://www.fabral.com/grandrib-3-load-tables/), spanning 24 inches the wind load is good for 213 psf. Converting psf to wind speed (P = .00256 x mph^2), would equate to 288 mph! For roof loads (gravity) 112 psf.

For shear loads – we actually tested 30 gauge steel (nearly 12% thinner than 29 gauge), over spans of 28 inches (nearly 17% greater than 24) and using SPF lumber. We were looking for a worst case scenario for roof applications. Without the use of sidelap stitch screws we obtained a tested value of 110 pounds per foot and with stitch screws 160 pounds per foot. These values are published in the NFBA Post Frame Building Design Manual.

Doing a little fuzzy math 160 X 1.17 (spacing adjustment) X 1.12 (thickness adjustment) X 1.18 (species adjustment) = 247 or roughly comparable to the OSB value!

 

So why would we even add OSB? Because in conjunction with the steel, the strength vales of the two products in withstanding wind shear can be added, up to twice the value of the lesser strength product.

Moral of the story – OSB has its place structurally in limited circumstances on post frame buildings, but to try to sell it in overall use as a benefit, just doesn’t hold true.