Roof Truss Spacing Explained for Ontario Builders
Roof truss spacing plays a critical role in the roof’s material efficiency, structural performance, and long-term durability. Key factors you must keep in mind when spacing roof trusses in Ontario include:
- Snow loads
- Roof pitch
- Span length
- Roofing materials
These factors will help you determine whether the spacing your roof requires fits into the standard range of 16 or 24 inches or if it needs adjustments.
When building roof trusses, the focus shifts to the style of trusses rather than the spacing between them.
But here's the truth: spacing matters almost as much as style, and defaulting to common layouts might not be the best solution for your project.
In fact, roof truss spacing in Ontario demands serious consideration as the province’s climatic conditions tend to present unique challenges that affect the longevity of most structures. Getting truss spacing wrong can adversely impact how loads are shared across the system. For example, wider spacing puts extra pressure on each member, while narrow spacing makes the entire structure stiff.
How the roof handles dead, live, and snow loads is also impacted. Incorrect spacing can lead to deflection – which is why following “rule of thumb” assumptions is a bad idea.
In today’s blog, Fonthill Lumber Inc., Ontario’s leading custom truss manufacturer, will show you how to space roof trusses correctly while keeping the province’s unique climate in mind.
Standard Roof Truss Spacing In Residential Construction
When it comes to residential roof trusses, the average spacing measures either 16 inches or 24 inches. Each of them can influence how your roof performs in the long run. Let’s break down both spacing conventions, along with a third one – 12 inches – to see how they stack up.
Note: This measurement is generally applied from the truss’s center to its ends.
16 inches on center
One of the most common spacing measurements, 16 inches on center, guarantees a higher load capacity while reducing the chances of deflection. You also get better performance when snow builds up on roofs. Most builders actually prefer this spacing – especially if they are using heavier roofing materials or building roofs with lower pitches.
24 inches on center
Using 24 inches of spacing is the best way to increase material efficiency. That said, this spacing is quite wide, which means it significantly increases the load demand placed on each truss. Ergo, it is best to custom-order these trusses. Professional truss manufacturers, such as Fonthill Lumber Inc. for example, will ensure the fabrication of stronger top chords. They will also verify snow load compliance to ensure your roof stays strong, no matter the season.
12 inches on center
A less common truss spacing size, this one is used for roofs with higher load demands. The reason for high load demands could range from the installation of heavy roofing systems to exceptional snow loads and structural redundancy. In any case, this is another option to consider if your project requires it.
When non-standard spacing is considered
If your project has certain design constraints, unusual spans or loads that exceed assumptions, you must consider non-standard spacing.
Factors you should take into account for residential roof truss spacing include:
- The roof’s span length
- Its pitch
- Weight of roofing materials
- Snow load requirements
- Truss load requirements
How Snow Load Impacts Roof Truss Spacing In Ontario
Snow load is one of the heaviest loads Ontario roofs face all year. The roofs you build should be able to withstand their weight without deflecting. That said, the impact of snow load is varied and requires careful consideration.
Understanding ground snow load values
Regional snow load maps play a major role in building design in Ontario. However, there is no fixed snow load value. It is critical that you factor in local building code requirements before determining appropriate roof truss spacing for your Ontario project.
Roof slope and snow accumulation
Based purely on mechanics, roofs with lower slopes tend to retain snow longer, which tremendously increases their live load requirements. On the other hand, steeper roofs tend to shed snow much faster. However, they bring their own share of different force vectors that need to be accounted for.
Heavy snow regions vs moderate zones
The northern parts of Ontario, along with its lake-effect zones, experience higher snow accumulation. If your project is located in this region, you need roof trusses that feature large members and closer spacing – something only custom systems can provide.
Engineering adjustments for winter conditions
With custom-engineered trusses, you get the flexibility to adjust individual elements to ensure they meet the unique demands of your project. For example, you can not only demand custom chord sizes and web configurations, but you can also get desired plate strength and spacing logic to build a truly enduring structure.
Evaluating Snow Load Influence
To determine the impact of snow load on your project, you must determine the following:
- The local snow load zone specific to your project
- The pitch of the roof you intend to build
- The weight of the roofing materials used
- Values specified in truss engineering data
- Validated spacing requirements against your project’s structural design
Roof Truss Spacing Vs Span Length
Roof truss spacing and span length are more closely connected than you think. One invariably influences the other, which makes it critical to understand the connection between them.
Relationship between span and spacing
First, let’s talk about their connection. As the span of a truss increases, the force placed on its individual members and chords increases exponentially, too. So if you have a truss with a longer span, it makes sense to have closer spacing.
Load-bearing walls and support points
This depends entirely on the layout of the home you’re building. Open-concept homes put extra pressure on the trusses due to the absence of support points. Meanwhile, layouts that allow for the installation of interior supports reduce span length and enable wider spacing.
Effects of attic storage or occupancy
If you are building a home that has an attic or a bedroom right under the roof, you have to factor in the increase in live loads. Such spaces tend to have greater structural demands, thus requiring reduced spacing.
Why longer spans often require closer spacing
Roofs with larger spans can increase the likelihood of bending, deflection, and joint stress. The only remedy to all of these issues is to implement tighter spacing.
Getting your roof truss basics right will further help you in truly grasping the concept of span and spacing and how they are interlinked.
Spacing Differences In Various Roof Truss Types
When it comes to residential roof trusses, each truss type brings its own unique spacing requirements, which you need to be mindful of when placing an order for your choice of a roofing system.
King Post Trusses
For king post trusses, the combination of shorter spans and closer spacing works best, especially because they have limited internal web support.
Fink Trusses
Fink trusses are probably the most efficient roof truss type out there. They can manage loads quite effectively, so you can implement wider spacing. However, we would recommend placing a custom roof truss order in that case.
Scissor Trusses
Scissor trusses can manage snow loads well. They also increase interior heights. However, they introduce horizontal thrust. That means reduced spacing is preferable.
Post-Frame Trusses
With post-frame systems, wider spacing is the norm. Their larger structural members and different load paths are best handled by wider spacing.
You can always speak to your truss designer to figure out the best spacing length for your truss type. They will guide you well.
Residential Vs. Post-Frame Truss Spacing
The requirements of residential truss spacing are bound to be different from post-frame truss spacing. Understanding how they differ can help you make the right choice for your construction project.
Standard residential framing spacing
All residential construction projects in Ontario typically stick to either 16-inch or 24-inch on-center truss spacing. That is because this is the most reliable and safest option. Both of these spacing sizes maintain the structural integrity of roofs without compromising their ability to bear snow loads. That said, if wider spacing is required, it must be verified by a certified engineer.
Wider spacing in post-frame construction
The spacing requirements of post-frame truss systems are wildly different. In fact, they can be as wide as 4 to 12 feet! The major reason behind such wide spacing can be attributed to either the presence of extremely large truss members or the use of different load transfer methods.
Load path differences
One of the major differences between residential systems and post-frame systems is how they handle loads. While the former relies on distributed loads, the latter is dependent on concentrated supports. Naturally, this influences their spacing requirements.
Engineering role in non-standard layouts
For non-standard roofing layouts, custom engineering is the only way to achieve the right spacing. This ensures the final spacing aligns with the structural capacity of the roof.
Residential Spacing Decision Factors
These factors will finally determine the roof spacing of your residential construction project:
- Construction type
- Intended building use
- Type of roof covering
- Local building code requirements
- Recommendations by the structural engineer
How Roofing Materials Affect Truss Spacing
So far we have discussed how snow impacts spacing. But did you know the materials used to build roofs also play a huge role in the final spacing size? Let’s explore:
Asphalt shingles
Using asphalt shingles to build roofs is a sure-fire way to increase their durability. These roofs tend to have moderate dead load requirements, which makes them the ideal candidate for spacing sizes 16 inches and 24 inches.
Metal roofing
Metal roofing is considerably lighter than asphalt roofs. However, wind uplift is a real factor when it comes to their construction and should factor in the ascertaining of their ideal spacing size.
Tile or heavier roofing systems
The increase in dead loads is significant when you use tiles or other heavy roofing materials. In such cases, it is best to resort to reduced spacing. Using engineered trusses might also help you manage their dead loads more efficiently.
Sheathing thickness and performance
Lastly, you must account for sheathing. Thicker sheathing might improve the stiffness of your overall roof system, but it does not eliminate the need for maintaining proper spacing. That is still critical to ensuring the structural integrity of the entire system.
When Builders Should Consider Engineered Truss Design
Fabricated or custom-built trusses can be the right choice for your project in several cases. Let’s explore a few major instances of the same:
Complex roof geometries
Lots of projects in Ontario require the installation of roofs with complex geometries. For example, valleys, hips, and intersecting rooflines can complicate load requirements, which only custom trusses can solve.
High snow or wind exposure
The climate conditions of Ontario are far from forgiving, and can greatly impact the long-term performance of a roof. If you want the roof you build to hold its own long-term, opt for engineered trusses.
Custom home builds
Custom home designs rarely ever sync with traditional spacing assumptions. So if you want to get their spacing right, you know what to do.
Mixed-use structures
Elements such as the construction of storage units, mechanical loads, or future occupancy demand require engineered verification and the construction of custom trusses.
In all of these scenarios, having custom-made residential roof trusses is a great way to achieve predictable performance and code alignment.
Choosing Roof Truss Spacing During Project Planning
All said and done, choosing roof trusses and determining their appropriate spacing is still a difficult task. However, it can be simplified if you employ these best practices.
Early coordination with suppliers
Make spacing decisions way before framing begins. Ideally, at the design stage of the truss itself. This requires coordinating with your truss engineers at the planning stage.
Integrate structural plans
To ensure you get the spacing right, make sure it aligns with the truss’ load paths, sheathing layouts, and mechanical runs.
Avoid costly spacing changes mid-build
Early planning and coordination, along with structural alignment is key to preventing expensive mid-project adjustments.
Conclusion – Getting Roof Truss Spacing Right The First Time
The aim should be to get roof trusses that already feature the right spacing. After all, proper spacing is key to preventing issues such as deflection and fatigue. The best way to ensure you get spacing right the first time is to match it with the climate-driven load requirements of Ontario.
That said, correct spacing should ideally be a design decision instead of a guessing game, and the right truss manufacturer can help you with that. Fonthill Lumber Inc. provides custom-made roof trusses tailored to Ontario climate and code requirements. Contact us to know how our properly spaced trusses can help your project.
FAQs
What are standard roof truss spacing sizes in Ontario?
Most residential roof trusses in Ontario feature either 16-inch or 24-inches on center spacing. This value is dependent on the project’s load requirements.
Is 16 or 24 inches better for roof trusses?
With 16 inches, you get a higher load capacity. With 24 inches, you get better material efficiency. The right choice depends on your project’s goals.
How does snow load affect roof truss spacing?
With higher snow loads, reduced spacing is recommended. The converse holds true when snow loads reduce.
Can roof truss spacing vary by roof type?
Yes. Factors such as roof geometry, span, and use influence spacing to a large extent.
When should builders consult a truss engineer?
You should consult a truss engineer any time your project’s spans, loads, and materials go beyond standard assumptions.
