Tag Archives: double trusses

Torn Between Two Lovers

In reader JEREMY from GOSHEN’s case, he is torn between two methods of post frame construction, rather than one hit wonder Mary MacGregor’s 1976 tune “Torn Between Two Lovers”. 

JEREMY wrote, “I’m torn between trusses on 4′ centers and what you do the double trusses every 10 or 12”.

Mike the Pole Barn Guru says:

It can be a tremendous pressure to build ‘just like everyone else does’. Because if everyone else is doing it a certain way, then it must be right. Right?

I can assure you trusses placed every four feet is merely how most builders in your area choose to assemble their buildings. In much of post frame construction’s world, engineers, architects and builders happen to place double trusses every 10 to 14 feet, with 12 feet happening to be most common. From a structural aspect, I prefer this wider spacing and doubled trusses. Every pair of trusses rests securely into a notch cut into columns. This physically makes it impossible for a truss to slide down a pole. Trusses are physically connected to each other face-to-face. This reduces risks of one single truss having a weak point, failing and pulling the rest of the roof down with it. With trusses ganged in this fashion, need for lateral bracing of truss chords and webs is reduced.

All roof purlins are connected to truss sides with engineered steel hangers. Trusses on carriers (headers between columns) often have under designed connections – not enough fasteners from carrier to column and truss to carrier. Nailed connection between purlins flat across truss tops is also problematic and in most instances is inadequate to resist design wind uplift loads. (more about this subject here: https://www.hansenpolebuildings.com/2014/04/nationwide-2/) Most post frame buildings with columns every eight feet also have ‘barn’ style wall girts – placed wide face to wind on column faces. Other than in very low wind applications and sheltered sites are these adequate to meet minimal building code wind loads. To read why girts installed this way fail to meet Building Codes please read https://www.hansenpolebuildings.com/2012/03/girts/.

From an aspect of ease of construction – wider spacing means fewer holes to dig (worst part of any post frame building). It reduces the total number of pieces having to be handled by roughly 40%. It makes it possible to assemble entire bays of roof on the ground and lift or crank into place using winch boxes. Safety and speed are paramount to how I prefer to build, being able to do this much assembly on terra firma meets both of these requirements.

What Kind of Trusses Are Pictured?

What Kind of Trusses Are Pictured?

This question was posed by Hansen Pole Buildings’ Designer Doug. Photo isn’t of a Hansen Pole Building, probably raising questions in Doug’s mind as it looks rather foreign.

Only actual trusses in photo are in raised center portion of this monitor style building. Interior trusses were probably sold to building owner as being “double trusses”. In actuality this system has only a single truss placed upon each side of columns. These trusses, even though only inches apart, do not load share. They are only as strong as weakest individual truss. Between trusses, sticking up beyond top of top chords are paddle blocks (read about paddle blocks here: https://www.hansenpolebuildings.com/2012/05/paddle-blocks/) to attach roof purlins.

Monitor wings (or side sheds/lean-tos) have rafters placed each side of columns with paddle blocks as well. Second floor (aka loft) extends out into wing areas, although quickly loses functionality as headroom decreases close to eaves.

More headroom could have been garnered throughout entire second floor had trusses and rafters been positioned to allow roof purlins to joist hang into their sides. When placed as “top running” purlins, interior clear height decreases by purlin thickness. Positioning of roof trusses as lowered, below purlins causes builder to have to frame outriggers (or tails) above truss in order to support sidewall overhangs. Each paddle block makes for a purlin stagger and eliminates one’s ability to predrill roof steel panels. This adds to possibilities of roof leaks being created by each stagger point.

Other concerns exist in this photo. Where roof purlins overhang single end truss, attachment has been made with yet another set of paddle blocks. With an assumption overhangs will be enclosed, this allows for outside air to enter in spaces created between purlins. This decreases efficiency of dead attic space airflow from eaves to ridge.

Solid blocking should be placed between end overhanging purlins to provide continuity of a load path from roof diaphragm to ground. As being built, load path has been divided.

Perimeter beams in this photo show to be inset between the columns. My curiosity wonders how they adequately attach? Your guess is as good as mine.

 

Horse Barn Trusses, A Pole Barn Face lift, and Double Trusses

Today the Pole Barn Guru answers questions about custom trusses for a horse barn, a face lift for a pole barn and where to use double trusses.

DEAR POLE BARN GURU: Hi,  I am looking to build a horse barn next spring, and had a question on the trusses that you offer. The barn will be on a 12×14 grid with a 14 foot aisle and 10 bays, giving it a width of 42 feet and length of 62 feet (the bays on one end will be 14 wide instead of 12 to make the two stalls on the end 14×14). I would like to use scissor trusses to make it more open and space them 12 feet apart. Instead of 2×6 lumber for the trusses, I would like to use 4×6, or even 6×6, to give it more of a timber look. Can you guys engineer and build trusses like that? Thanks. THOMAS in LOUDON

 

DEAR THOMAS: I will make a recommendation here to allow your aesthetic needs to be met, as well as giving you a horse barn with better interior air flow. Go to a pole and raftered design (read more here: https://www.hansenpolebuildings.com/2012/08/stall-barn/).

 

DEAR POLE BARN GURU: I have a pole barn in need of face lift. Can a kit be designed for an existing pole barn? It is 58 by 25. JERRY in TROY

DEAR JERRY: Although outside of our core business, it could be possible – we’d need to have some direction as to how far you would like to take it.

Here would be our recommendations:

-Remove all roofing and siding as well as entry doors.


-Add 12″ enclosed overhangs (could be possible, depending upon current interior structure).


-New steel roofing and siding to include wainscot panels around lowest approximately 3′ of building.


-Install Weather Resistant Barrier between wall framing and siding.


-Replace entry doors with new insulated commercial steel doors with steel jambs.

It might be possible to leave steel roofing in place and overlay it to create overhangs, however more information would be needed before making this recommendation.

 

DEAR POLE BARN GURU: If I were to use the double truss system would the gable end need to be doubled too? Or just interior ones? RANDALL in WRIGHT CITY

DEAR RANDALL: Typically each gable endwall would have just a single end truss. Some possible exceptions would be if you were designing to be able to extend building length in future, or for airplane hangars where there exists added strength requirement in order to support weight of a door.

 

 

 

 

Connecting Trusses Not Dots

Connecting Trusses Not Dots

This feature is probably not overly mentioned, however as most structural failures involve connections, it probably should be.

FEATURE: Double trusses notched into sidewall columns and connected with Strong-Drive® SDWS TIMBER Screws

BENEFIT: Trusses placed in a notch cannot slide down columns and Strong-Drive® SDWS TIMBER Screws resist uplift forces without a need for boring holes through columns.

WHAT OTHERS DO: A myriad of design solutions exist.

For trusses mounted every two or four feet upon truss carriers (headers between sidewall columns) attachment can be by toe-nail or engineered steel hangers to carriers. In some instances paddle blocks are inserted between carriers and trusses are nailed to these blocks.

With single trusses aligned with sidewall columns, trusses are most often placed into a notch cut into one side of columns. With nail or glu-laminated columns an interior column ply can be cut short to create an integral notch. Truss to column connections may include nails and/or bolts.

In designs with two single trusses, most often a truss is placed on each side of sidewall columns on top of bearing blocks. Bearing blocks may be nailed, lagged or bolted to column sides. Trusses are attached in same fashion as bearing blocks. Trusses are spaced apart along their length by paddle blocking installed between chords. Under extreme loading conditions trusses and their bearing blocks have been seen driven down sides of columns to rest upon building contents or even, the ground.

A variant on this places trusses closer together so they may be notched into sides of each column. This allows for elimination of bearing blocks and their associated challenges.

At Hansen Pole Buildings, we have trusses physically face-to-face nailed providing for a true load sharing between trusses. A notch is cut into one side of columns for trusses to bear. Attachment of trusses to columns is most often done by use of Strong-Drive SDWS Timber screws.

WHAT WE DID IN 1980: Lucas Plywood & Lumber placed a single truss upon each side of columns, on top of a nailed on bearing block. Trusses were attached to columns by means of a ¾” diameter, non-galvanized through bolt – entailing having to drill through nearly nine inches of wood and hoping to avoid steel connector plates at each truss heel.

 

Dead Load, Sliding Barn Doors, and Truss Spacing

This weeks PBG discusses a bottom chord dead load, installing sliding barn doors, and truss spacing.

DEAR POLE BARN GURU: Ok, just to make sure I understand that 10lb psf dead load rating would cover the bottom chords supporting ducts either resting on or suspended from them inside the conditioned space? My thinking is if the vents are within the conditioned space I would need minimal insulation to prevent surface condensation. ROB in ANNAPOLIS

DEAR ROB: 10 psf dead load is primarily to cover weight of ceiling gypsum wallboard. Your relatively light duct could be placed anywhere within roof system without adverse effects. A down side to placing duct work within a conditioned attic – effectively insulating roof slope plane and endwall triangles. For practical purposes this can only be achieved with closed cell spray foam. While being highly effective as an insulator, about R-7 per inch of thickness, it comes with a price tag not for those who are faint of pocketbook – usually around a dollar per square foot per inch of thickness. If you go this route, you need to eliminate venting eaves and ridge.

DEAR POLE BARN GURU: Good morning,

Figure 27-5

I need to get some pricing on a (2) 6’-0” wide x 8’-0” high sliding barn style doors for an agricultural building in Ware county Ga.

 

I have never purchased, or installed a door like this, so I was hoping you could help me get started.

 

Thanks, DAVID in KENNESAW

DEAR DAVID: Thank you very much for your interest. Hansen Pole Buildings only provides doors along with an investment in a complete post frame building kit package, due to high incidence of damage when shipped independently. We do have installation instructions available online: https://www.hansenpolebuildings.com/2016/07/build-sliding-door/.

 

DEAR POLE BARN GURU: What would the truss spacing need to be in our area that has a 40lb snow load? RODNEY in REPUBLIC

joist hangersRODNEY: In most instances a true double truss (not two single trusses spaced apart by blocking) will be most cost effective, as well as adequate to carry applied loads (along with properly sized roof purlins). However, depending upon a myriad of other factors such as eave height, truss span, roof slope and building length some other spacing may result in cost savings.

This will be just one reason I recommend consulting with a post frame building kit supplier who has sophisticated design software able to do a near instantaneous analysis of multiple possibilities. This supplier should also be able to provide site specific plans for your building, sealed by a registered design professional.

 

 

Installing Joist Hangers

Installing Joist Hangers on Opposite Sides of a Double Truss

My friend and loyal reader LONNIE in COLORADO SPRINGS is one Hansen Pole Buildings’ client who truly puts thought into the assembly of his new post frame building.

Lonnie writes:

“I’ve been pondering and pondering this and I may have a solution that I want to run by you. I’m considering buying a Bostitch F21PL framing nailer to use on the project and mainly because it includes a metal connector tip that will allow it to drive the 3” nails through the hangers for the purlins. What I was thinking of doing is to frame each truss bay using 2@ 1 1/2” 10d nails (always making sure to use the same 2 holes for each hanger… i.e. upper left and lower right) to build each bay on the ground. After raising the truss bays, go back and attach the double trusses together and at the same time finish the hangers with two 3” 10d nails in the empty hanger holes. The only concern I had was that the 3” nails would be driven opposing the 1.5” nails on the opposite truss hanger. However, since the nails would be driven point to point I think the odds of the 3” driving the opposing 1.5” out would be very slim. 

Do you think that mix of 1.5” and 3” nails for the connectors would be sufficient or should I really consider just temporarily attach the hangers and replace the temporary attachment with the 3” nails? If that is the case, is there an issue driving 3” nails basically tip to tip through the hangers?

Mike the Pole Barn Guru writes:

Your mix of nails will be more than adequate, as the load carrying capacity of the hanger is greater than the ability of the roof purlin to carry a load. In simple terms – the hanger and its fasteners are not the weak link in the system. Also – if you take two hangers and place them back to back, you will notice the holes do not all line up – whether the variability is accidental or purposeful, I do not know, however it further reduces the probability of nails from opposite directions exactly hitting each other tip-to-tip.

A caution – situations involving a differentiation from what is shown on the actual engineer sealed plans should always be verified for structural adequacy prior to implementation.

 

It Is Exactly the Same Building: Part II

Well, maybe not exactly the same building.

Yesterday I ran a beginning list of comparison’s between a Hansen Building quote and a quote by one of our competitors espoused to be “exactly the same” by a client of ours.

The saga continues:

Powder coated diaphragm screws vs. #10 diameter painted screws . Those who are familiar with the properties of paint and powder coating know the first is far superior. Some more information on powder coated screws is available here: https://www.hansenpolebuildings.com/2012/08/lobular-powder-coated-screws/. There are structural challenges which occur when using industry standard small diameter screws, which we found out about only when we went to test a building roof: https://www.hansenpolebuildings.com/2012/08/this-is-a-test-steel-strength/.

 

Recessed purlins vs. stacked purlins. Stacked purlins go over the top of the interior roof trusses, which effectively lowers the truss by the thickness of the roof purlin, hence reducing interior clear height – you get less volume of usable space! Stacked purlins also attach to the trusses via “paddle” blocks, which are highly problematic: https://www.hansenpolebuildings.com/2012/05/paddle-blocks/.

Bookshelf girts vs. flat girts. Wall girts placed flat on the outside of columns rarely meet with the deflection criteria of the Building Code as can be found here: https://www.hansenpolebuildings.com/2012/03/girts/.

Inside closures at eave vs. no eave closures. Inside closures keep the flying critters out of your new post frame building. https://www.hansenpolebuildings.com/2015/12/the-lowly-inside-closure/.

True doubled trusses vs. Single trusses each side of columns. When two trusses are spaced apart by blocking, they no longer act as an integrated pair, each truss functions on its own. In the event of a critical roof load, if the weakest link is a flaw in one of the trusses, the entire roof could easily land on the ground. With true double trusses, they load share – and since the probability of two trusses having the exact same weak point is extraordinarily small, an overloaded roof is more likely to stay standing after the single truss roof has gone boom.

Engineered steel hangers to attach purlins and truss bracing vs. Nailed connection. There is a reason Building Officials like engineered steel connectors – they are a stronger connection! https://www.hansenpolebuildings.com/2013/08/simpson/

Ledgerlocks to attach trusses to columns (eliminates drilling huge through bolt holes) vs. Bolts. We are into providing buildings which are structurally sound as well as easily constructed by the average person who can and will read English. This truss to column connection is both!

Engineer sealed plans and calculations vs. not sealed plans. My long term readers have read my harping on engineered plans. Here is why: https://www.hansenpolebuildings.com/2016/10/engineer-stamped-pole-barn-plans/

500+ page Construction Guide. Let’s face it, it does not matter how good the design or materials are, if there are not explicit instructions on how to get everything together right. I’ve seen plenty of post frame building kit packages instructions in my nearly four decades in the industry. Absolutely nothing compares to what we provide.

Getting a better “deal” on a post frame building than what was quoted by Hansen Pole Buildings? And of course it is “exactly the same building” – let us review any competing quotes you are considering. The service is absolutely free of charge and if it is indeed an equal to or better building, and a better price, we will be the first ones to tell you so!

Dancing With the Posts

Reality television watchers have suffered through 384 episodes of the ABC networks, Dancing with the Stars hosted by Tom Bergeron since 2005. On occasion, it seems some of our clients (or much more often their builders) have done some posts (as opposed to pole) dancing when placing columns for their new building. A certain amount of randomization can be accommodated, as found in this real life scenario:

Our client contacted his Hansen Pole Buildings’ Designer Rick recently, with this information:

“(name withheld) has a question about what to do with the bottoms of his posts being off and how it will affect his roof purlins. 

He sent this diagram showing how his posts are off: 

pole layout

Red circle is 3 inches off 

Blue circle is 1 ½ inches off 

The question is, does he just set the tops of his columns where they are supposed to be, or does he add a 2×6 to the side of one post?”

From front to back on the left side of the building the now poured into concrete column spacing is: 120”, 144”, 144”, 144”, 119.5”. Other than the rear bay being ½” short, it is spot on.

Now, for the right side – 117”, 145.5”, 144”, 144”, 121.75”. Those of you who pulled out your calculators already know the right side is ¾” longer than the left, as well as the columns not aligning.

In the most typical (as it allows for least cost, fewest holes to be dug and more long term design flexibility) Hansen Pole Buildings construction, double trusses are notched into the sidewall columns and 2x purlins are joist hung on edge between them. For ease of construction and builder sanity, it is ideal for the purlins in each bay to be able to be cut to the same length.

There is a solution, which I passed along:

“Construction Tolerances Standard for Post-Frame Buildings” allows for columns to be 1% out of plumb, which on a 16′ eave would be 1.92″.

He certainly wants to have trusses placed on columns so as to be able to cut all of the purlins to the same length in each bay.

Working from bottom of page up –

First pair up page (diagram sent by client) – tip left column forward (down page) 1-1/2″, right rear (up page) 1-1/2″

Next three on left tip forward 1-1/2″

Rear – left corner tip outward (back) 1/2″ right corner tip forward 1/4″

The posts will easily flex this far, so it shouldn’t be a huge issue.

This is just one of many reasons why post frame building roofs should be framed (as well as sheathed) prior to any wall framing being done. In the event the walls would have been framed prior to this, solving the challenge would have proven to be difficult, at best.

Thankfully, we have a very astute client who contacted our Technical Support Department for assistance as soon as they were aware of something gone awry.

Nailing Trusses Together

A Truss Story…

I began my career in the prefabricated metal plate connected wood truss industry back in 1977 at what was then Spokane Truss, now it is a ProBuild truss plant. From there my next stop was their sister plant Coeur d’Alene Truss (now Coeur d’Alene Builders Supply).

nailing trussesIn my two plus years with them, in many different capacities, we never nailed multiple ply trusses together – we did not even have a nail gun at either facility! We couldn’t have nailed trusses together if we wanted to.

When the housing market down turned in August 1979, I began my search for better opportunities. At my first stop I found out why truss manufacturers don’t nail trusses together…..

The now defunct Tilton Truss in Woodinville, Washington was my first “port of call” in my search. As I was given the tour of their plant, I saw some truss manufacturing equipment I was unfamiliar with – the steel connector plates were being air nailed into place by the truss builders, and then pushed out of the building and through a roller press. I looked up at the ceiling. The ceiling was covered with literally thousands upon thousands of nails….I now knew what truss builders were doing with their spare time!

I ended up spending 23 years in the truss industry, most of those in an ownership position.
There are many reasons for a truss company to not be nailing trusses together – besides the obvious safety issues.

Most truss manufacturers are set up so the trusses travel through a set of “finish rollers” placed in the wall to do the final seating of the pressed in plates. Once the individual trusses are outside of the building, mechanical stackers tip each truss up onto either bunks or finished truss carts. In order to nail two trusses together, they would need to be individually manhandled onto a location which was clean, flat and has no traffic – nailed together, and then placed in yet another location for storage until shipping. Hugely labor intensive.

Truss builders are not carpenters. They are trained to build trusses. The expectation of them being able to perfectly align two trusses each and every time – and properly nail them together is fraught with the possibility of failure. They just don’t have the set-up, equipment and time to do it exactly right every single time.

The truss company needs to turn a profit to stay in business. They make money by building trusses. Fifteen years ago I figured the average truss builder would build at least $1000 of trusses every day. Somewhere between 50 and 60% of a truss cost is materials, the balance is labor and profit. In today’s world, a truss manufacturing operation manager would need to charge out at least $120 per person hour to nail those trusses together.

In the plant, if damage is to happen to a truss, it almost universally comes from handling with a forklift or forklifts. Trusses nailed together – one of them gets damaged and needs to be repaired, now we are talking some work as the trusses need to be pulled apart and all of the nails removed!

On the jobsite – it is far easier to maneuver trusses together as individual units, those two ply trusses would prove to be backbreakers.

When the joist hangers for the roof purlins are installed, the flange towards the double truss should be attached with 10d common nails. These three inch long nails will aptly connect the two trusses together at the location of every roof purlin, in most cases taking care of around one-half (if not more) of the required top chord nails.

In the end, we want to deliver the ultimate post frame (pole) building experience. For those who desire the trusses to be nailed together, in the plant, we will happily ask (upon your request) if it is something they will do and if so, what the charge would be. This allows each individual client to determine the most efficient and cost effect situation for their own individual project.

Dear Pole Barn Guru: Can I Use Spray Foam Insulation in My Pole Barn?

Welcome to Ask the Pole Barn Guru – where you can ask questions about building topics, with answers posted on Mondays.  With many questions to answer, please be patient to watch for yours to come up on a future Monday segment.  If you want a quick answer, please be sure to answer with a “reply-able” email address.

Email all questions to: PoleBarnGuru@HansenPoleBuildings.com

DEAR POLE BARN GURU: In northern Idaho, just east of Coeur d’Alene, I had a pole barn put up without insulation figuring I would build 2×6 walls between the posts and insulate with batts and then plywood the walls later for a work shop. Can spray foam be used instead? Could I frame 2×4 walls instead of 2×6? Can it be sprayed onto the metal siding and roof without any negative effects showing up later? I will have a heater in there, but probably not on full time. QUIRYING IN COEUR d’ALENE

DEAR QUIRYING: Can you use spray foam? The answer is yes, however it is probably the most costly choice, and the Building Code requires any spray foam to be covered with non-combustible material (e.g. gypsum wallboard).

For the walls, you could frame a non-structural 2×4 studwall, holding it flush to the inside of the columns, and place batt insulation between the studs. The studs do not have to be the same depth as the insulation, and in doing so, you will eliminate a thermal bridge.

Beware, less costly (per inch of thickness, not R value) open cell foams are permeable to moisture – so condensation could become an issue. To obtain an R-19 rating from spray foam, be prepared to spend around $3 to $4 per square foot of insulated area.

While spray foam is relatively light weight, always check with the manufacturer of the roof trusses and the Registered Design Professional (RDP – engineer or architect) who designed your building to verify the weight of the insulation being added will not compromise the structural integrity of the building.

DEAR POLE BARN GURU: I sent in three pole barns that i am looking to get a quote for. my families barn just recently burned down a few days ago due to undetermined causes. We lost our animals in the fire which was devastating. Our pigs and chickens were our livestock and our food. We need to get a barn up and built soon to get our farm running again. I have a few questions about this, first off if i go ahead and purchase this kit how does it get delivered to my house. Second, if this is purchased is the supplies all in one kit that you ship out or is it a list a what we need and i have to get it? please get back asap thank you. NEEDY IN NEW YORK

DEAR NEEDY: I am deeply sorry for your losses. Fire is so devastating.

When you order from us, the materials are delivered to you via truck.

You are purchasing from us the design, the complete 24″ x 36″ blueprints which are specific to your building and show where every board is placed. Not only to we provide all of the materials for construction, but we give you detailed instructions as to how to assemble everything.

DEAR POLE BARN GURU:  What is your standard design practice to accommodate a wider O/C truss?  Double the truss? Or increase the truss member sizes?

VASCILATING IN VERSAILLES

DEAR VASCILATING:  Our most common practice design in general is a system using doubled trusses spaced most commonly every 12′ (although spacings 10′-16′ are also very common). The doubled (or more technically “ganged”) truss system affords some safety not found in single truss systems – as multiple trusses physically connected to each other all for true load sharing. The probability of two or more connected trusses having the exact same weak point is phenomenally low – reducing the risk of a catastrophic failure in an extreme loading situation. Ganged trusses also require less bracing than single trusses, adding to ease of installation, as well as lower costs and a “cleaner” finished appearance.  It also may mean no cumbersome (and expensive) truss carriers.  Lastly, if you put overheads in a sidewall, having the double trusses mean you could put as wide a door as 12’, and have plenty of room to put in a hoist system to lift a vehicle between the sets of trusses.

Vascilating then responded:

Thanks for the quick response. I assume, then, the practice is to utilize 12′ 2×6 purlins placed on edge on top of those trusses?

Is the spacing of 12′ the same for an attic truss? I recently got a quote from Hansen for a gambrel building with which I intend to have attic trusses. Is it common practice to finish a room using the knee walls of those trusses?

Dear Vacilating:

Every client gets my individual and undivided attention for as long as they need to get their questions answered.

The snow load will dictate purlin size, but they will be 2×6 or larger, joist hung between the trusses. Attic trusses will be the same, however may be more than just a 2 ply truss depending upon the span and load. Most typically people will finish those spaces with a knee wall.

Unless you are absolutely married to the gambrel look, the most efficient and cost effective design for multi-story space, is to just design a multi-story building. For about the same cost, you can get full room height from sidewall to sidewall

 

 

Single Truss System: Purlins Laid Flat

Before any of my readers drop their teeth due to me saying something I don’t exactly extol… is easy….read on!

I’ve spent the last few days in Michigan – where I am being told no Building Official would EVER approve of a pole building designed with double trusses spaced 10 or 12 feet on center and 2×6 or 2×8 purlins on edge. To the contrary, I’ve been involved in the design of about 15,000 buildings designed exactly this way. Throughout the Western United States, the typical post frame construction utilizes the concept of pressure preservative treated columns, spaced 10, 12 or even 14 feet on center, with two ply trusses, aligned with the sidewall columns. Literally hundreds of thousands of buildings have withstood snow loads to upwards of 200 pounds per square foot (psf) and wind speeds far over 100 miles per hours (mph).

The originally patented post frame (pole building) design concept utilized columns spaced every 12 feet. Even the unimpeachable source of all knowledge (Wikipedia) references columns spaced every 12 feet (https://en.wikipedia.org/wiki/Pole_buildings).

In post frame construction, roof purlins are the members running the lengthwise direction of the building, either placed on top of, or between the roof trusses (or rafters), to attach the roof steel or other roof sheathing to.

To the good folks in Michigan, the only way to construct a pole building, is to place the columns every eight feet. Truss carriers (basically headers) are then run from column to column. The trusses are installed on top of the carriers, every four feet.

This four foot truss spacing, allows for 2×4 roof purlins to be placed flat on top of the trusses. These purlins are attached by driving nails through the wide face of the purlin, into the tops of the trusses. It does make for a fairly easy purlin install (other than dimensional lumber typical runs about ¾ of an inch over length, so every purlin must be trimmed), and it gives a big wide surface (3-1/2 inches) to run screws through the steel roofing, into the purlins.

Like any system, there are some downsides – and my opinion is this method has some significant ones, which outweigh the positives.

In comparing to my idea choice of construction, this method requires 50% more holes to be dug. It takes half again more trusses and involves handling about double the number of framing members. Granted, often the framing members are smaller, but handling is still handling.

Structurally, there do exist some issues. The great majority of building failures are from connections – either inadequate, or improperly installed. The fewer connection locations, the less places for a potential error.

The trusses every four feet, columns every eight, results in purlins having to be connected to trusses, trusses to truss carriers, truss carriers to columns. Lost is the direct truss to column connection provided by them being aligned with each other.

In a single truss system, if one truss fails due to extreme loads, the balance of the roof is sucked down behind it. The face-to-face connected double truss system, creates a redundancy where no two adjacent trusses share the identical weak link. This load sharing prevents many would be failures.

With the single truss system, as each truss is only 1-1/2 inches wide, requires double the lateral bracing against buckling of a double truss (three inch wide system). Again, more pieces, more connections, more possible locations for failure.

And one more thing – I mentioned nailing the steel to the purlins on the 3-1/2” face as being an easy target to hit.  However – what about nailing the 2×4 purlins where they come together over a single truss?  You now have two purlins butting into each other, sharing that 1-1/2” space.  The chances of missing the truss beneath, or splitting either the end of the 2×4 and/or the ¾” space on the truss are….pretty high.  Another connection failure.

And back to the Building Official issue – our company has dozens of clients all across the state of Michigan who have been granted Building Permits and are enjoying their buildings with double trusses and wall columns spaced every 12 feet. Never be able to obtain a permit? Never is a big word, and it just is not the case.