Tag Archives: column spacing

Is the Double Truss System Stable for the Midwest?

Is a Double Truss System Stable for the Midwest?

Reader SHARON in NORTH DAKOTA writes:

“Dear Pole Barn Guru,

I have attached some pictures of a 62×96 pole barn with 12ft sidewalls. I am rather ignorant about truss systems, but this one looks atypical to others I have seen. What type of truss system is this, and is it stable for the midwest? How are your truss systems different? 

Thank you for your time and knowledge.”

Mike the Pole Barn Guru responds:

What you are looking at is a “double truss” system, where two roof trusses are physically joined side-by-side with the use of mechanical connectors (most often nails). It is absolutely stable for anywhere in the world. The most common Hansen Pole Building design utilizes the double truss system, typically with sidewall columns spaced at 10, 12 or even wider column spacing depending upon applied wind and snow loads as well as door locations. In the case of the photos you have sent, the roof purlins were placed over the tops of the trusses and staggered every other bay, this precludes the ability to pre-drill the roof steel, which would have minimized (or eliminated) the possibility of a roof leak caused by a misplaced screw. The Hansen Pole Buildings’ double truss system utilizes engineered steel connectors to attach the roof purlins to the sides of the roof truss top chords, as opposed to merely attempting to adequately nail through purlins to the tops of the trusses. The superior holding power of this connection resists wind uplift forces which could otherwise tear a roof off and send it swirling off like Dorothy’s home in The Wizard of Oz.

The most popular article I have written is on truss spacing – you can read it here: https://www.hansenpolebuildings.com/2011/06/pole-barn-truss-spacing/.

A caution – in the photos you have supplied, the trusses have knee braces, which could lead to a collapse if not engineered and accounted for within the truss design. More on knee braces here: https://www.hansenpolebuildings.com/2012/01/post-frame-construction-knee-braces/

The benefits of double truss systems vs. single truss systems include:

1- Fewer holes to dig for truss bearings – with columns every 12 feet, it reduces holes by 1/3rd.

2- Fewer columns to have to set.

3- Reduces total number of boards and trusses having to be handled and installed by as much as 50%.

4- Eliminates possibility of the one single weakest truss failing and pulling the balance of the roof down behind it.

5- Reduces the need for lateral bracing – a properly connected together double truss is twice as stiff in resisting buckling in the weak direction.


What Size Post Spacing?

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: Building a 32’x 50′ barn that’s 32′ high. Trying to determine the extension out from the ridge for the widow’s peak/ hay hood. Didn’t know if there’s a correct mathematical equation for this? PHILIP IN NEW KNOXVILLE

DEAR PHILIP: There is some mathematics involved, but it comes from a structural standpoint, rather than aesthetics.

A widow’s peak is an extended pointed overhang placed in the center end of a barn roof. Historically, they were used as a pulley support to raise hay bales into hay lofts. In modern post frame construction, very few widow’s peaks are actually used functionally, other than as shelter to protect a loft door. More often than not, they are strictly for aesthetics.

The width of the widow’s peak is usually 1/3rd to ¼ of the width of the gabled end of the building. The distance extended beyond the building endwall, or other endwall overhang is up to the eyes of the beholder, but is most typically three feet.

Now for the math…..the roof surface of the widow’s peak must be accounted for in the design of the endwall truss, as well as the supporting roof purlins. The truss manufacturer needs to be aware of the dimensions of any overhangs beyond the end of the building. The supporting roof purlins can be capably designed by the RDP (Registered Design Professional – architect or engineer) who has done the building design. The nicest looking widow’s peak at time of construction, can end up being far less than pretty if it sags over time.

Mike the Pole Barn Guru

DEAR POLE BARN GURU: What is your typical post spacing and what is the maximum spacing the poles can be spread out? RICK IN WATERLOO

DEAR RICK: The most efficient post spacing is going to depend upon the wind and snow load conditions at any particular given pole building site. As a general rule, the best “bang for your buck” is most typically spaced every 12 feet, although 10 foot and 14 foot spacings are often a close second.

On fully enclosed buildings, the wall girts normally become the dictate on how far apart columns can be placed – they usually will fail at 16 foot pole spacing (again, depending upon wind loads).

For buildings where one or more sidewalls are partially enclosed, 24 foot spacings between columns can be fairly easily accomplished. On endwalls, with a clearspan truss, it is possible to have posts only at the building corners.

Mike the Pole Barn Guru

DEAR POLE BARN GURU: Does Macomb Township allow pole barn construction for a garage? Do you work in Macomb Township, MI? PETE IN MACOMB

DEAR PETE: Pole barn (more technically “post frame”) construction is a 100% code conforming construction system. I’ve found jurisdictions which have tried to prevent “pole barn” construction within their jurisdictions, and we have successfully won the battle every time. Jurisdictions can legislate what a building looks like, however it would be improper to attempt to limit a conforming structural system.

Should you (or any other reader) find a jurisdiction which has contrary ideas, please let me know – as I will have a friendly (and persuasive) discussion with the jurisdiction’s legal counsel.

Macomb Township does have an unusual requirement for any type of building – “rat walls”. You can read more about them here: https://www.hansenpolebuildings.com/2012/06/rat-wall/

As to where we do work, Hansen Pole Buildings provides complete custom designed pole building kit packages anywhere in the United States – including Macomb Township.

Mike the Pole Barn Guru

DEAR POLE BARN GURU: I want to add a lean-to on my 42 x 48 pole building. Should I attach 2×10’s to the poles and put purlins on top of them as if continuation of the building, or should I put a ledger across the side and build accordingly. Thanks DION IN RUHKAMP

DEAR DION: Your cart may be slightly ahead of your horse. Before looking at the rafters and purlins, it might be a good idea to read: https://www.hansenpolebuildings.com/2015/07/shed/

Back to your original question – I personally prefer to attach the rafters directly to the columns with roof purlins on edge in between the rafters. As to 2×10’s – depending upon the width of the shed and your snow load, it is not likely they are adequate. With more information, I can give you a more definitive answer.

Mike the Pole Barn Guru