Principles of Roof Truss Design: Calculate Truss Dimensions

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roof structure

When you walk into many modern buildings and houses, you’ll quickly notice trusses use to give the roof stability and strength. Wondering how much a design like that costs? What dimensions do you need? You could use a roof truss calculator to find these answers, but first, you need to understand the basic principles of roof truss construction.

This post will discuss some of the most important elements of roof trusses – and how dimensions are calculated. Keep reading to begin your journey to the perfect roof truss design.

What Are Roof Trusses?

Roof trusses use straight pieces of wood to form triangles, which then support heavy loads commonly. A roof truss bears the weight of the building’s roof. The parts of the triangles experience tension and compression, but they will not yield under the load.

Why are these so popular now?

Well, there are a few reasons. Most importantly, roof trusses are economical – they use construction materials efficiently and allow for easy transportation and assembly, especially compared to other roof structuring options.

Frame Construction Of A Truss Roof With Hurricane Tie Down

As you begin learning about roof trusses, you’ll find that the truss’s structural height must be larger than the height of similar structures that use solid beams – rather than triangles. This isn’t a disadvantage, but rather another advantage. The size of the beams, and their angles, allow for excellent roof drainage and water tightness.

The Different Shapes of Roof Trusses


You won’t be surprised to hear that flat trusses are used for buildings with flat roofs. They look very similar to floor trusses, but they still provide a great deal of support. However, they don’t give the roof any slope, which doesn’t help shed water and debris.


The “gable” category of trusses encompasses several different types, including:

  • King Post
  • Queen Post
  • Howe
  • Double Howe

These trusses are used on pitched or peaked roofs and are one of the most popular types. They offer great support, and they can be used on fairly large buildings (commercial or residential).


A single-pitched roof only has one surface, and its trusses are quite simple. The goal is to support terraces or homes with more modern roof designs economically.


A “hip” or “hipped” truss is used to give the roof slopes on all four sides, which then come to a point in the middle. This is a smart truss design for buildings in windy or snowy areas. They’re very stable but also architecturally pleasing.

These are just a few of the most popular truss types. To learn more, or to browse the other kinds of trusses out there, talk to our experts.

Now we come to the actual “calculation” part of the truss design process. Bear with us as we introduce some numbers and formulas.

How Truss Loads Can Be Combined?

Roof Truss Construction

Understanding the loads your trusses will endure is more complicated than it might seem. You’ll need to consider various factors, from maximum wind loads in the area to snow levels and precipitation expectations.

Let’s say you’re designing a roof truss set up for an area with plenty of wind and snow. You’ll end to examine snow as a significant impact and wind as the critical “life load.”

What’s a live load? In the simplest of terms, this is the amount of force (temporary or transient) acting on a building. In this example, it’s the wind.

You will then use the following formulas to calculate your roof truss load combinations:

Case (1): Total load S’1 = 1.0 G + 0.9 Qsnow + 0.7 Qwind
Case (2): Total load S’2 = 1.0 G + 0.9 Qwind + 0.7 Qsnow

Look complicated?

We don’t blame you for thinking so, but that’s what we’re here for with our roof truss calculator and knowledge. We’re experts at understanding the difference between dead loads and live loads, and we’ll ensure your truss design will weather whatever is thrown at it.

What Dimensions Do You Need?

This is where our expertise comes into play. The average roof truss project costs between $7,200 and $12,000 – and much of that price discrepancy comes from the number of materials used – and, therefore, the project’s dimensions.

Hitek Truss Roof Truss Calculator

To help you out, we’ve created a handy tool that calculates the rake length of your roof. In other words, this roof truss calculator uses the span, overhang, and pitch dimensions to calculate a rake length. Using this information, you can better estimate how much the roof truss design will cost and what materials you will need.

Ensuring Roof Truss Stability

Using roof trusses isn’t a surefire way to ensure lateral movement is prevented or that the structure is entirely stable. You need to understand what forces will be exerted on the truss and what kind of restraining or bracing system will be required.

A great deal goes into ensuring each roof truss design we work on is safe and sound. We don’t just help you understand roof trusses and calculate their dimensions – we make sure that you’re building a secure, stable roof structure.

If you’re feeling overwhelmed or unsure, reach out. No design is too complicated or labor-intensive for our team.

Request a Calculation or Quote Today

With more than 75 years of combined experience in truss manufacturing, we’re quick to provide thorough, reliable pricing estimates. We promise to hide no costs, cut no corners, and leave no stone unturned when it comes to meeting your needs. All of our quotes also consider critical environmental factors, client needs, and fast turnaround times.

At Hitek Truss Design, we provide calculations and estimates for:

  • Roof Trusses
  • Floor Trusses
  • Custom Truss Designs

To begin building your roof truss quote, call 352-797-0877 or request a bid online. We’re ready to start your journey to the perfect truss construction project in Hernando, citrus, Pasco, Sumter, Hillsborough, Polk, Marion, and Pinellas counties.

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Nik Prodonovich