Tag Archives: post frame design

Why it’s Critical to Understand Lumber Species Groups

Why it’s Critical to Understand Lumber Species Groups

Originally published in SBCA Magazine January 6, 2024

For consumers of structurally graded lumber the two key elements of the lumber’s grade stamp are the assigned grade and the species or species group. These two elements establish what published design values should be referenced for that piece of wood, particularly when used in a structural system like a truss, roof rafter, floor joist, or wall. While it may seem straightforward, there are important differences to be aware of when using lumber from species groups.

Douglas Fir-Larch (DF-L) encompasses trees grown in three separate geographic regions in North America. The three regions are indicated on the grade stamp using the designations DF-L, DF-L(N), and DF(S)*. Any consumer of lumber from one or more of these species groups should treat each as a separate and distinct raw material for design, manufacture, and installation purposes. To understand why, it’s important to look at how these lumber species groups are manufactured and graded.

Lumber species groups exist because it is often not practical, nor potentially desirable, to separate individual species of logs when the lumber manufacturer processes them. While there are several reasons, some of the most prevalent include: forest conditions make it impractical to separate species during harvesting; visually differentiating many species is difficult and inefficient at the mill, once processed, some lumber species can’t be differentiated without the use of a microscope; and, some species have similar mechanical properties.

The American Lumber Standards Committee (ALSC) and Canada’s National Lumber Grades Authority (NLGA) recognize the DF(S) species group as douglas fir and bigcone douglas fir and DF-L species group as including douglas fir, bigcone douglas fir, and western larch. However, these trees are harvested from three different growing regions:

DF-L: Washington, Oregon, Idaho, Montana, Wyoming, and California

DF-L(N): Canadian provinces

DF(S)*: Arizona, Colorado, Nevada, New Mexico, and Utah

In addition to Douglas Fir-Larch (DF-L), other common species groups used in North America for structural purposes include Southern Yellow Pine (SP) and Spruce-Pine-Fir (SPF). The SPF species group is a combination of Canadian spruces, pines, and firs that share similar mechanical properties and growing regions. SPF(S) is a similar species group of spruces, pines and firs that originates in the U.S. SPF(S) has different design values from SPF. SP is a combination of four different species of pine in the U.S. South: loblolly pine, long leaf pine, shortleaf pine, and slash pine.

These different growing regions have an impact on the published design values under ALSC’s PS 20 lumber standard. Below are the design values in the American Wood Council’s 2018 National Design Standard (NDS) Supplement that correspond to each of the assigned species group based on the lumber grade:

Sometimes, DF-L and DF-L(N) or DF-L and DF(S)* will be combined at a manufacturing mill or at a reload operation. Again, these different species groups have different published design values and should be treated as separate raw materials. However, if that isn’t possible from a practical or efficiency standpoint, under ALSC rules the lower of the two species’ published design values must be used.

Introduction to Post-Frame Buildings

Introduction to Post-Frame Buildings

Rather than me chewing up a portion of your life you will never get back, I am deferring to Chapter 1 of NFBA’s (National Frame Builders Association) Post Frame Design Manual. Here is my overview when it was first published: https://www.hansenpolebuildings.com/2015/03/post-frame-building-3/

Please take a few moments to read this first chapter, if you are considering building, as it will put you a leg up on most providers and builders, as they are unlikely to have read it and know this terminology. https://associationdatabase.com/aws/NFBA/asset_manager/get_file/371354

Hire a Local Engineer and Work With a Lumber Yard?

Should I Hire a Local Engineer and Work With a Lumber Yard?

Let’s hope not. Here is the email which triggered this article:


I am building a 50×60 pole building with 22′ eaves. I’m shopping right now to either hire a local PE to design the structure and work with my local lumber yard to supply the package or maybe buy a kit like the ones you sell. Do you do custom sizes? Would you be interested in quoting my project?

I live in Lake Stevens, Washington.




Thank you very much for your interest in a new Hansen Pole Building.

About Hansen BuildingsThe heart of our business is providing totally custom designed post frame buildings of any size, as such your contact information has been forwarded to one of our senior Building Designers who can assist you with the process.

Some advice – hiring a local engineer to do the structural design will result in one thing for certain, and probably a second. The certainty is you will spend probably 8 to 12% of the value of your building on the engineer. In our case, the engineering is included with your investment in a new post frame building kit package. Our engineers do thousands of buildings for us, so your engineering costs are minimal.

The second is – most engineers are not specialists in post frame building design. You might get a great deal on the engineering itself, only to later find out your spent thousands (or tens of thousands) of dollars more than was necessary due to your engineer not being familiar with the most current advances in post frame design, as well as the plethora of materials options which could be incorporated to make your building the most efficient structure it can possibly be.

Your local lumber yard is most probably like most – they are nice, friendly, hard working folks, who know a little bit about lots of things. However, they are not going to be post frame building experts. The outcome, again, is probably going to prove to be one of less than ideal results.

My encouragement, whether you eventually invest in one of our post frame buildings or not, is to deal with folks whom you know are truly experts. We’d like to believe somewhere approaching 20,000 successful buildings might be heading us in the right direction.

Mike the Pole Barn Guru

Need an Engineer in Utah?

I’ve never met or spoken with engineer Max Gregersen, engineer. I don’t even know for certain if he is an excellent engineer or not. What I DO know is he is not so egotistical as to believe he knows it all and he will reach out to others for assistance. This in itself speaks volumes to me.

Max recently wrote to me:


I have a client who has requested post and beam with light frame wood framing using preformed metal panels for roof (standing rib) and walls (ribbed panels) in 2015 IRC Seismic Design Category D1 without plywood or OSB sheathing under the metal panels for the roof or walls. 

This would require the metal panels to act as shearwalls and roof diaphragm with a light-framed wood supporting structure.

  • Is this something that you have done any past residential home projects?
  • Are there any ICC ES reports or shake table testing your technical engineering team is aware of that covers this?


Max A. Gregersen, P.E., S.E.
Principal Structural/Earthquake Engineer

1143 Two Moons Circle
Ivins, UT 84738 USA

385.232.1747 “

And my response:

Dear Max ~

Thank you very much for reaching out to us. Any standing seam panels will have to be installed over 5/8″ CDX plywood and minimum 30# felt per manufacturer’s recommendations. You can read more here: https://www.hansenpolebuildings.com/2015/08/standing-seam-steel/

There are published tables of the shear values of various configurations of ribbed panels in the NFBA Post-Frame Building Design Manual (https://www.hansenpolebuildings.com/2015/03/post-frame-building-3/).

In most jurisdictions you should not even be questioned as to the validity of these numbers, as they not only followed rigid testing standards but have also performed admirably over the test of time.

You may want to have your client consider post frame construction totally, as opposed to traditional light wood framing as it offers a great deal of flexibility in design, lower costs and quicker construction times.

In need of an engineered post frame building in any state (or just want the peace of mind which comes with one)? Call us at Hansen Pole Buildings (866)200-9657. Need a Structural/Earthquake engineer in Utah, you might try Max!


SIPs (Structural Insulated Panels)

I like cool stuff. I’m never right at the front of the line for new bright shiny things – but I am close enough to check out the first few and see if the bugs are out or not.

SIPs, in my humble opinion, are pretty cool stuff. I’ve never been asked specifically by a client to design a post frame (pole) building with SIPs for the roof and walls, but I can see it coming soon as SIPs appear to be gaining in popularity.

SIP PanelWhat are SIPs?

From www.sips.org: “Structural insulated panels (SIPs) are a high performance building system for residential and light commercial construction. The panels consist of an insulating foam core sandwiched between two structural facings, typically oriented strand board (OSB).  SIPs are manufactured under factory controlled conditions and can be fabricated to fit nearly any building design. The result is a building system that is extremely strong, energy efficient and cost effective. Building with SIPs will save you time, money and labor.”

Here, in the very near future, I will be discussing the applications with the director of www.SIPSchool.org.

I will share with my readers what I learn, pretty much as I learn it. Hopefully with some practical applications.

In my ideal dream world, a post frame (pole) building skeleton (columns and trusses) would be erected, then large SIP panels would be attached to them. For best economy length multiples of 12’ would be used, so 24 foot long panels could be placed lengthwise on the building.

The lowest wall panels could be fabricated from pressure preservative treated plywood and embedded into the ground, as needed, to meet heat loss requirements.

My “new bright shiny things” are rarely the least expensive solution, but I can’t say I’ve regretted them – especially not in my own personal buildings. I’ve done some work for myself which had to be remodeled later, as the buildings were repurposed and I hadn’t given enough thought to what future uses might be.

I am looking forward to being educated, and if SIPs turn out to be what I think they might be – the post frame/SIPs combination could become very, very popular.

Interesting Use for a Pole Barn

I have configured both Google and Yahoo for notifications every time “pole barn” or “pole building” comes up in a new or edited article on the Internet. One of the things I am looking for is new or innovative ways people use buildings. Some of them make for interesting potential blog posts.

From Van Buren County, Michigan, yesterday, comes a story of an unsuccessful use of a pole barn:

It seems an 18 year old had perhaps been drinking, and decided to go on a burglary spree.

After entering one home, and appropriating some items, he decided to try the same with the neighbors. The suspect was unsuccessful in entering the home of the last victims, and woke them up in the process. He then forced his way into their pole barn, where the shotgun wielding homeowner held him at bay until deputies arrived.

The suspect was later charged with three counts of larceny from a motor vehicle, unlawful driving away of a motor vehicle, and alcohol consumption by a minor.

In retrospect, I suppose the owner of the pole barn in question, might view this as a case of successful, but unintended use of his pole barn.

Now I doubt law enforcement agencies are going to start constructing pole buildings with the idea they will become “mouse traps” for burglars….but it is an interesting concept!

pole-barn-weddingDo you own a pole building which is being used for a unique purpose? If so, I’d like to hear about it, and why you chose a pole building as opposed to some other form of construction.

Take a look at this photo from one of our recent customers who recently got married in his new pole building!

Post Frame Construction: Knee Braces

Coming from a background in the prefabricated roof truss industry, knee braces have always bothered me.

What is a knee brace?  I’m not talking about the type you wear for a dislocated or arthritic knee joint.

A knee brace is an inclined diagonal lumber member connecting to and extending from the sidewall columns, usually several feet below the truss to column connection, across and attached to the face of the trusses. They are intended to supplement the lateral resistance of post frames when loaded by lateral wind forces.

The intent of knee bracing is noble – to supplement the resistance of post frames (columns along with aligned roof trusses create a post frame) under lateral (wind) loads. They can influence the unsupported length of the columns. As the unsupported length of the column is reduced, it is less prone to buckle.

Pole building frames, prior to installation of roofing and siding, tend to be very flexible. It is the sheathing which makes the building stiff. It would not be unheard of to stand on top of the center of a framed up only building and be able to rock the building six to eight inches! Adding knee braces at this point of construction will stiffen the frame and act as a temporary brace.

The effectiveness of a knee brace is highly dependent on the stiffness of the connections to the post and the truss. If the connections at the ends of the brace are flexible or not very stiff due to the use of a few nails, the roof diaphragm carries the bulk of the load and the brace is ineffective. If the brace connections are made very stiff (by installing many nails or bolts) the brace could effectively resist the wind loading, but overload the truss.

Knee braces induce bending moments in truss chords. If used in a post-frame design, load sharing among the truss, post, knee brace, connections and roof diaphragm must be included in the structural analysis.

Johnston and Curtis, in 1984, performed actual testing on post frame buildings with and without knee braces. They concluded, “As loads were increased, the effect of the knee bracing became insignificant.” The study found knee bracing in post frame buildings provides very little support for horizontal loads. Two years later, as a result of their studies, Gebremedian and Woeste concluded, “Knee braces added little stiffness to the post-frame building analyzed.

In a presentation to the International Conference of Timber Engineering in 1988, Jerry Barbera (at the time chief engineer for the Pacific Northwest office of the International Conference of Building Officials) stated, “When the knee brace is placed on the truss at random the truss will experience considerable stress.”. Further, he said, “Thus the truss designer has to know what the extraneous forces are in order to design for their effects. Both designers have to communicate with each other”.

Walker and Woeste’s 1992 book Post Frame Design states, “Knee braces appear to be a “no-win” solution.”

In all likelihood, pole buildings being proposed as utilizing knee braces are a result of lack of knowledge upon the part of those who are providing the building. The knee braces add no benefit to the overall strength of the structure, while potentially adding loads into the roof trusses, which they were not designed to carry. In the right combination of circumstances, this could result in a catastrophic failure of the building.