Roof Trusses

Scissor Trusses   Attic Trusses   Spread Web Storage Trusses   Ag Trusses   Roof Truss Loading   Broken Truss?    Lateral Braces

 

Downloadable Roof Truss Terminology pdf

As building inspections and building codes become more stringent and engineer reliant, more and more builders choose roof trusses over stick framing. The advantages are clear:

  • Each component is engineered for its specific location
  • Design liability is placed where it belongs: on a structural engineer
  • Less time spent in framing
  • Less time with the floor and walls exposed to the weather
  • Complex roof lines are much easier to build with trusses
And it goes without saying that trusses allow for larger clear spans than stick framing.

We take pride in building the highest quality trusses in the business. From design to installation, we will be available to answer any questions you may have.

Scissor Trusses

Scissor Trusses can add a luxurious and spacious feeling to any room.

Scissor trusses, also known as cathedral trusses, have a sloped bottom chord

Normally, a scissor truss can be engineered with half as much slope on the bottom chord as the top chord. Of course that’s not a given. Low pitch roofs, such as 4/12 or less, may not allow for half the slope of the top chord. Conversely, steeper roofs may allow for more than half the top chord pitch, as in the truss shown above, where the top chord pitch is 10/12 and the bottom chord pitch is 6/12.

When quoting scissor trusses it’s important that we know the width of the wall on which they will sit, so that we make the seat cut the correct width.

The seat cut is the area where the truss sits on the wall. It must be the correct width for the wall on which the truss will be placed.

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Room-in-Attic Trusses

Attic trusses are a relatively cheap way to add either storage or living space.

Attic trusses that will be used as living area must be designed to a higher per square foot load, usually 40 psf live load, and may fall under local code requirements for room height. It’s important to know what those local requirements are when requesting a truss quote, so that we can maximize the available space in the truss.

Storage attic trusses are typically designed to carry 25 psf live load.  While trusses in a garage may not be tall enough to create a full size room, many of our customers have utilized that extra space by going with attic trusses. The one time cost of upgraded trusses may be well worth it in the long run.

Spread-Web design

Another option to add storage area without the full cost of an attic room is to use a Spread Web design.

Spread Web designs add triangular storage space

While a Spread-Web design is not quite as clean and open as an attic truss, it can be a very economical way to add storage space. And there’s no need to worry that the truss will not be loaded for the storage area. Simpson Strong-Tie’s engineering software automatically adds storage loads Spread-Web locations.

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Ag Trusses

Ag trusses are typically used for agricultural buildings such as hay sheds, machine sheds, or livestock shelter.

Ag trusses, like this 60 footer, are heavy and hard to handle.

While there are as many variations in ag trusses as in other trusses, ag trusses have one thing in common; they are always spaced further than 24″ O.C.

On Center Spacing on ag trusses can be anything over 2′ O.C. to 10′ O.C. We do not recommend greater than 10′ O.C. spacing. Typically an ag building has a tin roof. They seldom have a ceiling built in. If you do intend to have a ceiling in your ag building, it’s important to specify that the building will have a ceiling load when requesting a truss quote.  The roof is typically framed with purlins of either 2X4 or 2X6, placed flat across the trusses or vertically between the trusses.  It’s especially important with ag trusses to be sure that appropriate temporary and permanent bracing is installed .

As a small family owned shop, ag trusses are not our specialty. Although we can and do build them, our assembly process is quite manual, which makes them more difficult for us to handle.

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Roof Truss Loading:

Our roof trusses are currently designed under the following criteria:

  • Building Code: IRC 2012/TP 1-2007
  • Load Provisions: ASCE7-10
  • Roof Truss Standard Loads: TC Live – 20 psf; TC Dead – 10 psf; BC Live – 0 psf; BC Dead – 10 psf
  • Snow Load: 30 psf
  • Deflection: L/360

While we do our best to ensure that the trusses we design meet all the design requirements of the job-site location, it is ultimately the customer’s responsibility to verify that all local codes and requirements are met. We will of course change the designed code or loading to meet any specific requirement upon request.
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When Roof Trusses Break

No one likes to see it, but sometimes trusses break. When they do, it is usually because of mishandling during delivery or while setting the trusses. We strongly encourage our customers to thoroughly read the Job-Site package provided on truss delivery before handling the trusses. Doing so will greatly minimize the chances of injury to yourself or the trusses during and after installation.

Broken truss? here’s what to do
That’s a broken web

So a truss has a broken piece, or plates that have pulled apart. Unfortunately, it happens. Here’s what to do:

Contact us immediately with as much information as you can. We will need the truss number, the broken piece ID (it is labeled on the sealed drawings), the exact location of the break, with measurements either from one end of the truss, or the nearest joint. If possible, send pictures to us so we can properly assess the damage before passing it on to the engineer.

If the damage is greater than we can repair in-house, we will write up a detailed report of the damage, and send it to our engineers so they can design a repair. It typically takes about 24 hours to get repairs returned.

Never repair a truss until you have an engineer stamped repair in hand. Truss repairs are costly and time consuming; jumping the gun can add to the problem. If the truss is installed before the damage is noted, you must be aware that a damaged truss cannot be relied upon to support a roof or anything on it, especially including people! Take no chances of injury. Damaged trusses should be stabilized and repaired as soon as possible.

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Lateral Bracing

Lateral bracing on a truss web is noted on the sealed drawings as shown above. This symbol indicates that the web on that particular truss needs a brace.

You may wonder why the web needs a brace. To understand that, we need to understand the two opposite forces that act on the webs in our trusses: Compression, and Tension.

In this example, the left web is more likely to require a brace.

Our engineering software calculates all the forces in each truss member. When compression forces on a web are too great, it could bow out and potentially break under full load. In that case, the software notes that a brace is required. Sometimes we can up the grade on the web material to avoid our customers having to add lateral braces in the field, but we can’t avoid all lateral braces.

This is a good time to reiterate that we never use less than 2X4 material in our trusses. While using 2X3’s may result in some cost savings in the initial truss package, they would certainly end up requiring more lateral bracing, which means more work on your part. The greater potential for webs breaking during delivery and installation is another reason we never use smaller than 2X4 material of #2 or greater in our trusses.

There are multiple methods of bracing webs, depending on whether or not they lines up with other webs. Below is a link to bracing guidelines published by the Structural Building Components Association.

Lateral Bracing on trusses with dissimilar webs

Our Tools and Resources page has several more links that have to do with web bracing. Check it out here.

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Color Coding System

You might notice when you get a set of roof trusses from us, that they have different colors of paint at the splices, like this:Color graded boardsSo why do we do that?

First off, you need to know a little bit about lumber grades. Not every 2X4 is created equal. We stock a minimum of three grades of 2X4. For example, #2, MSR1650, and MSR2100.  “#2” is a visual grade, while MSR stands for “Machine Strength Rated”. When we design trusses, our software chooses from our available lumber grades to use the most cost effective lumber that will still meet the strength requirement for each truss component.

When we cut out a job, we batch the pieces for the entire job into one large cut list. When it is time to cut bottom chords, for example, the sawyer might have fifty boards that are identical, except for grade. So he cuts fifty boards from a variety of different grades. When he’s done, they look exactly the same on the lumber cart, except for the tiny grade stamp that may or may not show because it is only on one side of the board. This is dangerous, because it makes it too easy for the guys on the assembly line to throw in the wrong grade board on a truss. That’s why we devised our color coding system.

The color coding system that we use ensures we put the correct grade of board in each truss. The way it works is this:

  • Black = #2
  • Red = MSR 1650
  • Blue = MSR 2100

Now when our sawyer cuts those identical boards, he takes the time to grab a can of paint and paint each stack according to the grade they are. When the guys on the assembly line grab a board from the cart, they know at a glance what grade it is, and there is far less chance of putting the wrong grade in the wrong spot.

Identical boards, except for grade.

Of course, not every board needs to be painted. In some cases, there may not be more than a few identical pieces, and they are individually marked. Or, there may be a lot, but they are all the same grade, and so there is no need to mark them. That’s why you won’t see paint on every board.

Does this system take a little more time and effort? Of course it does. But it’s just one example of an extra step we take to ensure that the trusses you get will be built correctly. We think it’s worth it

Sample Color Roof Truss Layout

Below is a layout of a job we built in 2018. Our layouts feature full color, which helps to differentiate between trusses, walls, roof and ceiling planes, coffered or cathedral areas, and more.

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Ready to contact us for a quote?  Go here to e-mail us.

Further information about bracing, etc, are available on our Tools and Resources page

Why use country truss?
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