How Does Timber Species Affect Structural Performance?

Understanding Strength, Availability, and Design Impacts

When designing a heavy timber structure, one of the most important decisions happens before engineering calculations or joinery details: choosing the right timber species. While aesthetics, cost, and regional availability all play a role, the structural behavior of a species has a significant impact on member sizing, connection design, movement during drying, and overall project budget.

At Vermont Timber Works, we frequently work with Douglas fir, Eastern white pine, Eastern hemlock, Southern yellow pine, White oak, and glulam members. Each brings unique strengths and limitations to the table. Below is a detailed look at how these materials influence timber frame engineering.

Douglas Fir: Strong, Versatile, and Often the Best Species for Larger Frames

Douglas fir (DFir) is often the most expensive species per board foot, but paradoxically, it frequently becomes the most economical species once the engineering is complete.

Why? Strength-to-Weight Efficiency

Douglas fir offers one of the best strength-to-weight ratios of any commonly available North American softwood. Its high bending strength, compression strength, and stiffness allow for:

• Smaller cross-sections
• Smaller connections and joinery
• Better deflection performance
• More efficient handling and shipping

For long-span trusses, heavily loaded beams, and hybrid steel–timber structures, Douglas fir remains one of the most reliable and predictable materials.

Other Advantages

• Excellent availability in long lengths
• Consistent structural grading
• Predictable drying and movement

Douglas fir is often our default recommendation for architecturally exposed and structurally demanding frames.

Eastern White Pine: Lightweight, Easy to Work, Structurally Limited

Eastern white pine (EWP) is a traditional New England staple—lightweight, easy to cut, and visually soft and bright. Structurally, however, it has notable limitations.

Annual Growth Pattern = Knot Rows = Reduced Strength

EWP forms new branches at the top of the tree each year, creating a circular pattern of knots that remain embedded in the trunk. This results in:

• Poor bending capacity
• Reduced tensile strength
• More brittle bending behavior

Knots are unable to take tension in timber, which severely limits the structural capacity. Combined with its low density, EWP is not ideal for long spans or major structural elements.

Where It Works Best

• Decorative or non-structural timberwork
• Small buildings with modest loading

Eastern white pine is a beautiful and historic species—but not a high-performance structural option.

Eastern Hemlock: A Middle-Ground Option with Specific Limitations

Eastern hemlock sits between EWP and DFir on the East Coast—stronger than pine, but less predictable than fir.

Strength & Structural Performance

Hemlock performs well for:

• Short- to medium-span beams
• Rustic Rough-Sawn Frames
• Moderate truss designs

However, it lacks the strength and stiffness required for long spans or highly loaded systems.

Key Limitations

1. Limited availability in long lengths
   Sourcing hemlock above 20’—especially in large dimensions—is challenging due to heavy harvests and limited old-growth stock.
2. Shake in large timbers
   Hemlock is prone to shake (separation along growth rings), which can reduce:

• Shear strength
• Connection capacity
• Visual quality on exposed surfaces

For high-reliability structural designs, hemlock may not always be ideal.

Southern Yellow Pine: High Strength, High Density, Challenging Aesthetics

Southern yellow pine (SYP) is one of the most common timber species in the U.S., known known for impressive density and strength, rivaling or exceeding Douglas fir depending on the grade.

Structural Advantages

• High bending strength
• Excellent stiffness, compression, and shear capacity

This makes SYP an excellent option for heavily loaded members—when the right sizes are available.

Practical Challenges

• Limited availability in large timber dimensions compared to DFir
• More checking and surface cracking
• High resin content, meaning harder on tools
• Yellow color makes it a challenging species aesthetically for some frames.

For the right project, SYP is a great choice—but it’s not always easy to source in the sizes required for large timber frames and could be aesthetically challenging.

White Oak: Dense, Durable, Traditional — with Unique Structural Considerations

White oak is one of the most historic and well-known species in the U.S. Its density, color, and grain give it a character that no softwood can match. It is also one of the most durable domestic hardwoods, but is less structurally efficient than most think.

Dense Material = Superior Bearing Strength

White oak excels in compression perpendicular to grain, making it ideal for:

• Heavily loaded post bottoms or sill plates
• Beam-to-post bearing joints
• Wood-to-wood load transfer in traditional joinery (e.g., splines).

However, Density Brings Trade-Offs

White oak is:

• Extremely heavy to lift, move, and ship
• More difficult to cut, mortise, and drill
• Tough on tooling and machinery
• Harder to dry without moving and checking significantly

Large white oak members are labor-intensive and require careful handling.

Bending Capacity & Movement

Despite its strength in bearing, white oak is not as strong in bending as Douglas fir. This means:

• Long beams must be sized larger
• Truss members often become heavier

White oak also moves significantly as it dries:

• Checks deeply
• Twists or cups
• Shrinks more than softwoods

These characteristics are natural and expected—but must be accommodated in design and fabrication.

Glulam: Engineered Strength, Superior Consistency, and Exceptional Performance

Glued-laminated timber (glulam) is not a species but a material type—yet it deserves equal consideration when discussing structural timber options. Glulam timbers are usually comprised of either SYP or DFir lumber.

Although glulam is generally the most expensive option per board foot, it delivers significant engineering advantages that often justify the investment.

Younger-Growth, Regenerative Material

Glulam is made by laminating smaller boards—usually from younger-growth timber—into a single structural member. This approach allows for:

• More efficient forestry management
• Less reliance on old-growth trees
• Better use of smaller-diameter logs

This makes glulam one of the more environmentally regenerative timber options.

Reduced Defects and Superior Structural Predictability

Because glulam is composed of multiple laminations (lams), natural defects like knots or slope-of-grain deviations in a single lam have limited effect on the overall member. The result is a remarkably consistent structural material—far more predictable than solid timber.

Strength Advantages: Often 2–3× Stronger Than Solid Sawn

Glulam can be engineered for specific strength grades, resulting in:

• Much higher bending capacity
• High tension performance
• Increased stiffness
• Reduced deflection in long spans

For structural applications, glulam outperforms every solid-sawn species available.

Glulam beams and trusses excel in:

• Long-span roofs
• High snow-load regions
• Large commercial projects
• Curved architectural elements

Aesthetic Considerations

Some clients prefer the organic, continuous grain of solid timber and dislike the visible laminations in glulam. However, many architects and engineers appreciate:

• The clean, uniform appearance
• Reduced checking and movement
• Reliable long-term stability

For engineering-driven applications, glulam is often the favorite choice.

Comparison of Timber Species (and Glulam) for Structural Applications

Choosing the Right Species or Material for Your Structural Needs

Selecting the right timber is as much a structural decision as an aesthetic one. At Vermont Timber Works, we consider:

• Required spans
• Loading conditions
• Architectural style and visual goals
• Availability of long or large members
• Project budget
• Joinery style (traditional vs. steel-reinforced)
• Movement, checking, and shrinkage
• Need for engineered or high-strength materials

Douglas fir often delivers the best combination of strength, availability, appearance and cost efficiency. Southern yellow pine is excellent when open to appearance. Hemlock and white pine remain regionally appropriate choices for smaller traditional frames. White oak offers unmatched presence and durability for historic or “traditional” appearance frames.

And when long spans, high loads, or engineered performance are priorities, glulam stands in a category of its own as one of the strongest, most reliable, and most dimensionally stable timber options available.

If you’re designing a timber frame and want to explore species and engineered material options, we’re always happy to help evaluate what will work best for your project—structurally and visually.

📧 Email: [email protected]
📞 Call: 802-886-1917

About the Author