Truss Weight

Pole Barn Guru Blog

I have been asked this question more than a few times, by potential do-it-yourselfers, who are considering constructing their own buildings. Jeff, one of the Building Designers at Hansen Pole Buildings, got asked this very same question again yesterday.

I am certain most people ask this question, as they are considering how to go about lifting the trusses into place on their new buildings – by hand. My advice is – please use equipment. Lifting by hand is just an accident looking for a place to happen. Neither a broken truss, nor an injured person is worth the risk.

So, back to the question at hand….

Several factors are going to influence truss weight – how far does the truss span (the width of the building), what loads are carried by the truss, and what part of the country is the building in? To a lesser extent the slope of the truss will influence the weight as well.

The slope? Yes! In most cases a 4/12 roof slope is going to be the most efficient combination of load carrying ability and economics. Slopes flatter than 4/12, especially with wider spans or heavier roof loads, are going to need to be “beefed up” in order to carry the same loads as a steeper slope. As slopes get progressively steeper, the length of the top chord increases, as does the length of the internal members (the “webs”).

Where does span fit into the mix? In engineering calculations, the span of a beam (a truss is a beam) is squared. This means a 30 foot span is 50% wider than a 20 foot span, but must have 225% of the load carrying capacity! The load carrying capacity is handled by larger or higher graded material being used for the truss top and bottom chords, as well as the webs. Roof truss plates, the pressed in steel connectors, also get larger.

What loads are being piled on? Besides any snow loads, the trusses also must be able to carry dead, or permanent loads. Besides the weight of the truss itself, these would include roofing materials (steel roofing over purlins being relatively light, shingles over oriented strand board – osb, being eight to even 10 times as heavy).

Why would the part of the country make a difference? In most of the west, trusses are built from Western Hemlock (Hem-Fir), Spruce-Pine-Fir (SPF) or Douglas Fir (DFir or DFL). In the east and south, most often the lumber is Southern Yellow Pine (SYP). The weight of lumber is based upon specific gravity (G). For Southern Pine it is 0.55, Douglas Fir 0.50, Hem-Fir 0.43, SPF 0.42. This makes Southern Pine over 30% heavier than SPF!

With all of this said, the best I can provide is nothing short of PFA (Plucked From the Air).

My truss weight table per single truss:

24’ truss, 120-150#,

30’ 160-200#,

36’ 220-300#,

40’ 270-350#,

50’ 375-500#,

60’ 450-600#,

70’ 600-800#,

80’ 800-1000#.

Regardless of truss span or truss weight, use common sense when lifting the trusses into place.  Be careful and your roof system will perform admirably for generations.

9 thoughts on “Truss Weight

  1. Andy Borough

    Hello,
    I was wondering if you could send me a quotes of some trusses. I have included the specs below.

    –40′ Span, 8/12 Pitch, Length 60′, 24″ O.C.
    –35′ Span, 9/12 Pitch, Length 124′, 24″ O.C.

    Thank you,
    Andy Borough

    Reply
    1. polebarnguru Post author

      Andy ~

      You may want to consider roof slopes which would give an overall truss height of 12′ or less, including any overhangs.

      With that said, we would need to know where the trusses will be delivered to – city, county, state.
      What will the buildings be used for?
      What is the plate line height?
      What type of roofing material will be used? If steel, will it be over purlins or sheathing?
      Will the buildings be heated?
      Is the building site open to the wind or protected from the wind?

      Reply
  2. Russ

    I’ve got a 30′ by 40′ cinder block shop/garage on some property I’ve purchased outside of Nashville, TN. The current roof is an industrial flat roof and is completely rotted and falling in. I’d like to replace it with a 4/12 pitch truss roof. I’m not going to store anything in the rafters and the walls are in great shape. The question I have is, can I truss this as a “one-man” show? Perhaps that’s a stupid question but I don’t have much help in the area due to being a new Northern transplant. I was going to have Lowe’s deliver the trusses. Any thoughts, suggestions, warning, help, forums, youtube videos would be appreciated. I’ve never put trusses up before, however I’ve done just about everything else over the years.

    Reply
  3. Charles harris

    I have a nightclub and I want to know if the roof trusses will accommodate the weight of a new soffit. The soffit weight approx. 4000.00 pounds with 1/4 ” drywall. The studs are metal. The truss are 36″ in height. The truss extends from one end to the other….approx.50′ long. My soffit is 14′ × 19′. Supported with (14) 3/8 × 6′ threaded galvanize rods. 3/8 beam claps at top of truss……will these trusses hold the weight?

    Reply
    1. admin Post author

      I would be absolutely amazed if the trusses you have on your building will support your new soffit without some significant structural modifications to the trusses. Your best bet – hire a local Registered Professional Engineer who can visit your nightclub personally, review the pertinent information and provide and engineered solution to your challenge.

      Reply
  4. Steve

    Hello, I live in Oklahoma and will be having a pole barn built soon. The size I had in mind was 50x60x14. The builder recommended 40′ trusses rather than 50′ due to the possibility of sagging later on. Should I be concerned that this would happen with 50′ trusses and go with his advice using 40′?

    Reply
    1. admin Post author

      Find a different builder (or better yet, buy an engineer design complete post frame kit package and do it yourself). Your proposed builder’s comment leads me to believe he has little or no structural knowledge.

      I have either installed, fabricated or specified prefabricated roof trusses for my entire adult life (over four decades) – for thousands upon thousands of buildings. It is not uncommon for 80, 90 and even 100 foot clearspan trusses to be successfully utilized in post frame construction with the possibilities of “sagging later on” being close to nil. A building is far more likely to show signs of roofline sagging from inadequate column footings, than from any truss issue.

      Reply
      1. admin Post author

        If you are asking about the wind loading – design wind speed and exposure would depend upon where you are along the coast, as well as distance from the ocean and whether your site is protected or not. Your local Building Department can provide specifics for your particular site.

        Reply

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