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.