# Dear Pole Barn Guru: How Much is Truss Weight??

New!  The Pole Barn Guru’s mailbox is overflowing with questions.  Due to high demand, he is answering questions on Saturdays as well as Mondays.

Email all questions to: PoleBarnGuru@HansenPoleBuildings.com

DEAR POLE BARN GURU: Hello, I’m an engineering student doing a research about sustainable buildings, can you tell me the approximate 20′ metal truss weight and 24′ wood truss weight?

DEAR CALCULATING: Nice to have engineering students reading this column!

Having been given no parameters for load carrying capacity, truss spacing or roof slope, leaves me just winging out an answer.

For wood trusses with a total load of around 180 pounds per lineal foot (30 pounds per square foot spaced one at six foot or two at 12 feet), a single 24 foot span 4/12 slope truss weight should be about 125 pounds.

I’ve never dealt with steel trusses, however I was able to find several formulas, as well as a table for calculating the steel truss weight, W being weight per horizontal square foot, S = span in feet, P = capacity of truss in pounds per horizontal square foot, and A the distance center to center of trusses in feet:

Charles Evan Fowler, P. E., for Fink trusses:

W = .06S + .6 for heavy loads; W= .04S + .4 for light loads.

H. G. Tyrrell, P. E.:

W = .05S+ distance center to center.

C. W. Bryan, P. E.:

W = .04S + 4.

M. S. Ketchum. P. E.:

+ For scissors trusses increase one-third.

Weight Per Square Foot Of Roof Surface For Steel Trusses

 6/12 Slope 4/12 Slope 3/12 Slope Up to 40 ft. 5.25 6.3 6.8 7.6 “ 50 ft. 5.75 6.6 7.2 8.0 “ 60 ft. 6.75 8.0 8.6 9.6 “ 70 ft. 7.25 8.5 9.2 10.2 “ 80 ft. 7.75 9.0 9.7 10.8 “ 100 ft. 8.5 10.0 10.8 12.0 “ 120 ft. 9.5 11.0 12.0 13.2 “ 140 ft. 10.0 11.6 12.6 14.0

As you can see – lots of opinions on the steel truss (as are probably huge variants in their configuration).

DEAR POLE BARN GURU:We’ve just had a 40’x60′ steel pole barn constructed (in the woods) for storing classic cars. We had the builder install and frame fiberglass insulation in. We’re installing OSB wall panels ourselves. Wondering if we should cover the fiberglass with ‘Visqueen’ for vapor barrier or would we be better served by installing foil faced OSB panels?

Thanks CONCERNED IN KOKOMO

DEAR CONCERNED: Most often fiberglass batt insulation which is used in walls has a paper (or “kraft”) facing on the inside, which when properly installed serves as the vapor barrier. If unfaced batts were used, then a clear plastic vapor barrier should be installed on the inside face. Foil faced OSB panels are designed to be placed below roofing to assist in keeping attics cooler in warm climates, it is not designed to be or replace vapor barriers in walls.

## 8 thoughts on “Dear Pole Barn Guru: How Much is Truss Weight??”

1. I want to build an 80′ wide by 100′ long riding arena attached to my existing barn. My existing barn is 24 foot from ground to the eaves and I want to attach the triangle shaped truss to the side of the barn to form a shed roof over the riding arena. The height of the chord needs to be at least 12 foot clearance. Is there problems with having an 80′ clear span with that type of truss, as far as engineering or components? Is the weight-bearing characteristics of the “shed roof” truss markedly different from the traditional peak-type truss?

1. Chris ~ Your “shed roof” or monoslope roof truss to span 80 feet can be done, but is probably not economically the best choice. The low end of an 80 span is going to be several feet thick, resulting in a very low slope roof – which due to the length of the panels will have to have one or more splices. All-in-all, it soudns to me like a recipe for undue costs and the potential to be less than happy with the end resultant.

2. Dear Pole Barn Guru,
Can I use two 100 foot trusses spaced five feet apart as a bridge if I connected them with four by fours for the planking of the bridge? What size material would need to be used in order to drive a small four wheel ATV across it? Could it be wood or would you have to have steel?

3. So I am building an indoor riding arena 70×200 and I am want it set on a concrete rim all around the outside edge. Do you know how deep the concrete has to be to support this weight?

1. At a minimum a concrete foundation wall will need to be at least below the frost line. This is a huge building and needs to be designed by a Registered Design Professional (architect or engineer), failure to do so could result in a catastrophic collapse.

As well, the trusses need some special attention:

This is an excerpt from Structure; August 2009, authored by Dr. Frank Woeste, P.E. and Dr. Donald Bender, P.E..

MPC is Metal-Plate-Connected; RDP is Registered Design Professional (architect or engineer).

Responsibilities where the Legal Requirements Mandate a Registered Design Professional for Buildings (Section 2.3 of ANSI/TPI 1)
“In preparation for specifying MPC wood trusses, every section of Chapter 2 and ANSI/TPI 1-2007 standard should be carefully studied by the RDP. In preparing this article, we assumed that the RDP will view a complete copy of Chapter 2 for a full understanding. Specific sections selected for discussion are cited by paragraph and subparagraph numbers.
Under Section 2.3.1 Requirements of the Owner, we note three sections that can help prevent truss erection accidents, and in some cases improve in-service truss performance. Over the past two decades, industry safety documents recommended that for truss spans over 60 feet, the Contractor should “See a registered professional engineer” for temporary bracing information. In many cases, Erection Contractors failed to follow the advice, and some accidents and performance problems stemmed from inadequate temporary and permanent bracing. The new ANSI/TPI 1 standard now requires action by the Owner and RDP as given in the following paragraphs:
2.3.1.6 Long Span Truss Requirements.
2.3.1.6.1 Restraint/Bracing Design.
In all cases where a Truss clear span is 60 feet (18m) or greater, the Owner shall contract with any Registered Design Professional for the design of the Temporary Installation Restraint/Bracing and the Permanent Individual Truss Member Restraint and Diagonal Bracing.
2.3.1.6.2 Special Inspection
In all cases where a Truss clear span is 60 feet (18m) or greater, the Owner shall contract with any Registered Design Professional to provide special inspections to assure that the Temporary Installation Restraint/Bracing and the Permanent Individual Truss Member Restraint and Diagonal Bracing are installed properly.”
The importance of these new paragraphs to truss safety and reliability cannot be overstated. When executed by the Owner and RDP, these provisions for long span trusses should be effective in preventing truss erection accidents and ensuring in-service truss performance. “

In summary – with trusses spanning 60’ or greater, the building owner has the legal obligation to contract with any registered design professional (RDP) for the design of temporary installation restraint/bracing and the permanent individual truss member restraint and diagonal bracing. And members added by your RDP beyond the original design, are outside of the scope of your purchase, and are at your expense to add. Further, your RDP is to make special inspections to assure the bracing they design, is properly installed.

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