Lumber, explained.

Lumber is one of the most widely used building materials in the world, yet it is often misunderstood. From how it is made to how it is graded, sized, and used, there is more to lumber than what you see on the shelf.

This page explains what lumber is, how it is produced, and how to understand the basics so you can make informed decisions, whether you are buying wood, building something, or simply learning.

Lumber is wood that has been processed from trees into standardized sizes and shapes for use in construction, manufacturing, and everyday projects. Most lumber begins as a log and is then sawn, dried, and finished so it can be safely and reliably used.

Lumber is commonly used for:

• Building homes and structures 
• Framing walls, floors, and roofs
• Interior finishes and trim
• Furniture and woodworking projects
   

Because lumber is a natural material, no two pieces are exactly the same. Grading and standards help make lumber consistent and predictable.

Lumber goes through several key steps before it reaches a lumberyard.

First, trees are harvested and transported to a sawmill. At the mill, logs are sawn into boards, timbers, or dimensional lumber. After sawing, lumber may be dried, either naturally (air-dried) or in a kiln, to reduce moisture content. Finally, it is planed smooth and cut to standardized sizes.

Each step affects how the lumber performs, how stable it is, and how it can be used.

When you see lumber labeled as a 2x4 or 2x6, you are seeing the nominal size, not the actual finished size.

Nominal size refers to the approximate size of the lumber before it is dried and planed. After processing, the finished size is smaller. For example, a standard 2x4 actually measures 1½ inches by 3½ inches.

These standardized sizes are used across Canada and North America so builders and designers can rely on consistency.

Lumber is graded to indicate its strength and suitability for structural use. Grading takes into account natural characteristics such as knots, grain direction, and overall quality.

Common grades you may see include:

• No. 2
• No. 2 and Better
• Stud grade
   

Higher grades generally allow fewer imperfections and provide higher strength values. Most residential construction uses No. 2 grade lumber because it provides reliable performance at a practical cost.

Structural lumber typically includes a grade stamp printed on the surface of the board. This stamp provides important information such as:

• The lumber grade
• Species or species group
• Moisture condition
• The accredited grading agency
   

The grade stamp confirms that the lumber has been inspected and meets recognized standards for structural use. In Atlantic Canada, this oversight is supported by organizations like the Maritime Lumber Bureau, which ensures lumber grading is carried out properly and consistently.

Lumber can be sold as green or dry, depending on how much moisture it contains.

Green lumber has not been dried and contains higher moisture levels. Dry lumber has been dried to a moisture content of 19 percent or less. Dry lumber is generally more stable, lighter, and less likely to shrink or warp after installation.

The moisture condition is usually indicated on the grade stamp using markings such as S-GRN, S-DRY, or KD (kiln-dried).

Lumber can be produced from many different tree species. In Canada, similar species are often grouped together for grading purposes.

One common example is SPF, which stands for Spruce-Pine-Fir. These species share similar strength properties and are widely used for framing and structural applications.

Understanding species and species groups helps ensure lumber is used appropriately and performs as expected.

Because wood is a natural material, it responds to changes in moisture and environment. As lumber gains or loses moisture, it can expand, shrink, twist, or crack.

Proper drying, storage, and installation all help reduce unwanted movement. Understanding how and why lumber changes helps users work with wood more successfully rather than against it.

Choosing the right lumber depends on how it will be used. Structural applications require properly graded lumber, while appearance-based projects may prioritize visual quality.

Things to consider include:

• Grade and strength requirements
• Moisture condition
• Species or species group
• Intended use and environment
   

Learning these basics helps prevent mistakes and improves long-term performance.