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Barn Screws Rotting Wood

Barn Screws Rotting Wood

Reader (and Contractor) JOHN in BIG RAPIDS writes:

“In a pole building constructed with trusses 2′ o.c 1/2″ OSB synthetic underlayment. We are finding out that the screw is riding the OSB around the screw. I have seen the same problem in standard pole barn construction with 2 x 4. Purlins. The screw will rot the wood and come loose. It is a problem with cold storage areas and condition space. We screw standing seam metal to 1/2″ OSB and nail shingles down with a straight shank nail. What is the issue with a barn screw rotting wood?”

You have a couple of different issues happening here.

First – screws will not hold in OSB, either with through screwed or standing seam panels. With standing seam, manufacturers typically recommend plywood substrates of at least 5/8-inch thickness.

Second – screws do not rot wood. It is a function of one or more of three things – screws improperly seated (screws into high ribs rather than flats; over or under driven; or not driven perpendicular to panels). Or, screws with neoprene gaskets (most are), instead of EPDM. Neoprene is not UV resistant, so quickly becomes brittle and cracks. Standard screws are #9 or #10 diameter and these narrow shanks will cause slotting of steel panels, over time, due to cyclic wind loads. Shanks are acting like knives! We found this when we did full scale diaphragm testing of steel panels over three decades ago. This was solved by our engineer, who did our testing, designing what is now known as “Diaphragm Screws”. Produced by Leland Industries in Canada, Hansen Pole Buildings provides them exclusively for through screwed steel panels. 1-1/2″ long, they are a #12 shank, except right below head (where screw passes through panels) it is a #14 diameter. These screws also have EPDM gaskets, have a JS1000 plating (read more here: https://www.hansenpolebuildings.com/2024/01/what-does-js-1000-screw-plating-mean-to-you/) and are powder coated, rather than wet painted.

Any of these conditions will allow water to seep around screw shanks and eventually decaying surrounding wood fibers.

On an unrelated note – we have clients in search of qualified building erectors in many markets. We connect you directly with client to quote your labor, no fees to us, no markup – strictly a service. You are also welcome to quote/provide any other services direct to client (site prep, flatwork, etc., even turnkey). This will be an ongoing relationship, not necessarily a ‘we have a client for you today’, and we will be promoting your business long term at no charge. We provide America’s strongest, fully engineered post frame building including full multi-page 24” x 36” structural blueprints detailing the location and attachment of every piece. All 3000f glulam columns, highest quality lumber (most 2400f msr, no standard or stud grade), framing connected with provided Simpson structural screws, delivered onsite. If interested please click this link: https://www.hansenpolebuildings.com/builder-application/

This entry was posted in Powder Coated Screws, Barndominium, Lumber, Pole Barn Questions, Pole Barn Design, Roofing Materials, Constructing a Pole Building, Pole Barn Planning and tagged diaphragm screws, EPDM gasket, screw patterns, post frame screws, rotten wood on January 16, 2025 by Rick Ochs.

Will I Have Issues With Post Frame Closed Cell Spray Foam Insulation?

Will I Have Issues With Post Frame Closed Cell Spray Foam Insulation?

Reader HEATH in NACOGDOCHES writes:

“I am building a pole barn that I do not plan to heat or cool initially, but would like to insulate due to condensation issues and our hot humid climate. Have there been issues with closed cell spf in post frame buildings. My main concern would be if there ever was a screw to back out and cause a leak. Probably overthinking it, but just trying to make a decision on what makes most sense. I am also open to soffit vents and installing a ceiling and blowing in insulation.”

Screws do not “back out”. Watch a screw being driven in – it pulls the wood fibers up. Wood has an inherent “memory” and as those disturbed fibers return to their natural state, they want to pull screws in (creating even a tighter seal).

Screw leaks are caused by either poor installation, wrong placement (on high ribs rather than flats), or entirely wrong parts. Poor installation will show up right away – either in a good rain storm, or by checking weather tightness by running a water hose on roof. I would recommend second of these prior to any interior finishes.

Most of our industry uses #9 or #10 diameter screws and often only an inch long. We found, under even a small load, one inch screws will pull out of lumber – so use 1-1/2″ screws. Next issue is one of time. Eventually slots will form around shanks of #9 or #10 screws, due to cyclic loading from wind. One these slots get long enough, they extend past screw’s washers and you have a leak. We use on larger diameter screw shank diaphragm screws to eliminate this as a challenge. Many are also using screws with neoprene rubber gaskets. These are not UV resistant and will break down due to sunlight. When this occurs, you again have leaks. There is an easy solution – EPDM gaskets. Yes, they cost a bit more, however damage from a single leak outweighs any up-front costs.

If you opt for closed cell spray foam, you want to have it applied directly to inside of steel panels, with no other barrier between insulation and siding or roofing. You will need to mechanically dehumidify, as your building envelope will be air tight. Given your climate, this would be my personal choice.

An alternative would be to blow in insulation over a ceiling. You should then order raised heel trusses to attain full insulation depth from wall-to-wall. Vent eaves and ridge in correct proportions and order roof steel with an Integral Condensation Control factory applied, to avoid having drips in your dead attic space.

This entry was posted in Pole Barn Heating, Insulation, Barndominium, Pole Barn Questions, Constructing a Pole Building, Pole Barn Planning, Ventilation, Powder Coated Screws and tagged spray foam insulation, post frame screws, condensation, post frame insulation, Ventilation on May 23, 2024 by Rick Ochs.

Thru Screwed Steel Screws – Pull-Over and Pull-Out

Thru Screwed Steel Screws – Pull-Over and Pull-Out

Hi, my name is Mike, and I am addicted to watching engineering disaster videos.

No, there is not yet a 12 step program for this addiction.

I have learned a few things from my addiction. When it comes to construction failures, most of them come down to connections. Connections (at least when wood is involved) take fasteners – screws, bolts, nails, wooden dowels, etc.

Now if one is getting parts manufactured say in China (as an example), there is a high probability they are going to fail under load – due to manufacturing process shortcuts. Biggest shortcut (and impossible to detect by eye) is under strength material.

When it comes to post-frame construction, most buildings are clad with roll formed steel roofing and siding. It is extremely durable, very cost effective and easily installed by use of thru screws.

At Hansen Pole Buildings, we provide only Diaphragm screws manufactured in Canada using North America components. These screws are a #12 diameter and 1-1/2 inches in length.

Now why would an assembly with a thru screw structurally fail (assuming product is manufactured of proper strength steel)?

Screws could pull out of wood. This would be a problem.

Over three decades ago, at an Alumax testing facility east of Los Angeles (Perris Valley), we constructed a full scale roof to test shear strength of steel panels. Our testing resulted in some surprises. Initially we felt our weak link would be framing under roof steel. We were totally in error and surprised at our results. Our assembly was done to match industry standards and included fastening steel to roof purlins using #10 x 1” screws every nine inches. As we placed horizontal loads into this roof, before ripples even appeared in steel roofing, screws started to pull out of framing. This pull out problem was solved by using 1-1/2” long screws.

Our next problem was roof steel began to slot beneath screw grommets. Solution here was to use larger diameter screws in high stress areas (at eave and ridge) and to place screws in this area on each side of each high rib, rather than along one side only. Only after all of these screw issues were solved, were we finally able to test our steel to failure. These results showed some fairly significant values. This test’s results are published in NFBA’s Post Frame Building Design Manual https://bse.wisc.edu/bohnhoff/Publications/Copyrighted/NFBA_Design_Manual.pdf See Table 6.1 (assemblies 13 and 14).

After our test was completed, Alumax’s design engineer, Merle Townsend, designed a screw specifically to solve weaknesses demonstrated by our test. Labeled as a “diaphragm” screw (https://lelandindustries.com/productpdfs/page%2001.pdf) this 1-1/2” part features a larger diameter shank than standard screws. A side benefit of this screw is this larger diameter helps prevent screw heads from twisting off during installation.

I did some looking at what published pull out values are for those #9 x 1” industry standard screws – only value I could find was 542# and it did not specify species of wood being driven into. Our diaphragm screw has minimum pull out values of 910# (Canadian SPF) and 1060# (Douglas Fir). in some instances – nearly double industry standard!

Besides pull out, another source of structural failure is pull-over. This is where screw remains in wood and steel roofing flies away. Besides washer/grommet configuration of screw, this is also going to be a function of steel panel thickness. Graph on Leland’s website displays a 26 gauge pull-over value of roughly 500#. Converting by dividing by 26 gauge minimum thickness (0.0187) and multiplying by 29 gauge minimum thickness (0.0142) provides a pull over value of about 380#. T

herefor pull-over is going to dictate before pull-out.

(Author’s note – having searched extensively, I have yet to be able to find a published pull-over value for #9 screws.)

For steel panels, screws in field (not ends of panels) are placed every nine inches. With screws into every purlin, spaced 24 inches on center, each screw is carrying 1.5 square feet of load. Our pull-over value of 380# divided by area gives a resistance per square foot of 253#.

Highest wind load areas are at perimeters of roof (Zone 3). At 200 mph (miles per hour) and a wind exposure C (fully open to wind in one or more directions), load on components and cladding in Zone 3 is 163.65 psf (pounds per square foot), based upon mean roof height of 15 feet. Even in wind exposure D (fully exposed to winds coming over large bodies of water) and making mean roof height 20 feet, load would be 208 psf.

Hansen Pole Buildings, having now provided well in excess of 25,000,000 diaphragm screws, has yet to have had a single screw fail in pull-out or pull-over.

Yes, these screws are more expensive, however we enjoy sleeping well at night knowing our clients’ steel cladding is not going to fail due to any screw issue.