Dimensional lumber, also known as S4S lumber (suraced four sides), refers to wood that has been cut and planed to standardized width and depth measurements for use in construction. Having a good understanding of dimensional lumber sizes is essential for any building or remodeling project. This comprehensive guide covers everything you need to know about the dimensional lumber sizes used in residential and commercial construction.
An Overview of Dimensional Lumber
Dimensional lumber provides a consistent and reliable building material for construction projects. The lumber is cut from softwood trees, typically pine, fir, or spruce. After logging, the raw wood is sent to a sawmill where it is cut, planed, and surfaced to achieve smooth, straight boards with uniform dimensions.
This process removes imperfections in the wood and creates boards where the final width and thickness is slightly smaller than the nominal size. For example, a 2×4 stud is not actually 2″ thick by 4″ wide, but is cut to the standardized 1-1/2″ x 3-1/2″ finished size.
The advantages of using dimensional lumber include:
- Uniformity – Pieces have standardized sizing which makes construction easier.
- Reliability – Quality grading provides dependable load-bearing capacities.
- Availability – Mass production makes dimensional lumber widely available.
- Cost – Relative to other building materials, dimensional lumber is an economical choice.
Understanding the different dimensional lumber sizes and characteristics will help ensure you get the right materials for your building or remodeling project.
Nominal vs. Actual Dimensions
The key thing to understand about dimensional lumber is that the nominal size and the actual size are different.
Nominal dimensions refer to the size name of the lumber, such as 2×4, 2×6, etc. These provide an easy way to identify common lumber sizes.
Actual dimensions are the finished measurements after the lumber has been surfaced and planed smooth. Actual dimensions will be slightly less than nominal size.
For example:
- A 2×4 has actual dimensions of 1-1/2″ x 3-1/2″
- A 2×6 is actually 1-1/2″ x 5-1/2″
This difference occurs because the logging and milling process removes about 1/2″ of wood from each surface. Having standardized actual sizes makes it faster and easier to work with dimensional lumber for construction.
Common Dimensional Lumber Sizes
The most frequently used dimensional lumbers have nominal sizes of 2″ x 4″, 2″ x 6″, 2″ x 8″, 2″ x 10″, and 2″ x 12″. Here are the actual dimensions for these common lumber sizes:
| Nominal Size | Actual Thickness | Actual Width |
|-|-|-|
| 2×4 | 1-1/2″ | 3-1/2″ |
| 2×6 | 1-1/2″ | 5-1/2″ |
| 2×8 | 1-1/2″ | 7-1/4″ |
| 2×10 | 1-1/2″ | 9-1/4″ |
| 2×12 | 1-1/2″ | 11-1/4″ |
Lumber that is 4 inches or less in nominal thickness is referred to as dimensional lumber. Pieces with greater thickness are called timbers or beams.
These standardized dimensional lumbers are used for the majority of residential construction and remodeling applications, including:
- Framing walls, floors, roofs
- Headers and beams
- Fencing
- Blocking and bracing
- Subfloors and sheathing
Matching the proper lumber size to the needed application will result in a safer, stronger finished product.
Characteristics of Dimensional Lumber
When purchasing dimensional lumber, there are a few key characteristics to take into consideration:
Species – Softwoods like pine, fir, and spruce are most common. Each has slightly different properties. Hardwoods are also available.
Grade – The grade indicates the lumber’s structural capacity and appearance. Grades range from low-quality economy stud grade to high-quality select structural.
Moisture content – New lumber generally has a high moisture content. More dried lumber is more stable.
Preservative treatment – Treated lumber protects against rot, fungi, and insects. Treatment is required for many exterior uses.
Surfacing – Most dimensional lumber has been planed to uniform thickness and width (S4S). Rough-sawn lumber skips this step.
Lengths – Dimensional boards are typically available in 8′, 10′, 12′, 14′, 16′, 18′, 20′, and 24′ lengths.
Dimensional Lumber Grades
Lumber grades provide an indication of the structural properties and appearance of dimensional lumber. Grades reflect the size and frequency of knots, checks, wane, and other natural characteristics.
There are several major grading agencies that inspect and grade softwood lumber:
- NLGA – National Lumber Grades Authority
- WCLIB – West Coast Lumber Inspection Bureau
- SPIB – Southern Pine Inspection Bureau
Common dimensional lumber grades:
Select structural – Highest quality grade with very few knots or defects, reserved for structural uses where high strength is needed.
No. 1/No. 2 – Have a somewhat higher number of knots and imperfections than select structural but still are high quality lumber.
Construction / Standard – Middle grade lumber suitable for most framing uses. Contains more knots but is still dimensionally stable.
Utility – Economical grade with knots and other defects permitted but still structurally adequate for general construction.
Stud – Lowest grade for use in non-critical applications like wall studs in normal conditions.
Choosing the appropriate grade for each application will provide suitable performance while making the best use of lumber resources.
Using Dimensional Lumber for Framing
The majority of dimensional lumber goes into building the structural framework or framing of residential and commercial buildings. Choosing the correct lumber size and grade is critical to achieve a structure that is stable, durable, and able to withstand expected loads.
Here are some best practices for using dimensional lumber when framing a structure:
- Use the tallest stud height possible (8′, 10′) to maximize wall heights and reduce joints.
- Select No. 2 or better grade studs for all load-bearing walls to get higher quality lumber with fewer defects.
- Increase stud sizes to 2×6 or 2×8 for taller walls or when spacing studs more than 16″ on center.
- Use 2×6 or larger for plates to get more nailing surface. Align joints between top and bottom plates.
- Select the tallest available lengths to minimize joints for headers, beams, and joists.
- Check moisture content of lumber to avoid twisted, bowed studs. Get kiln-dried lumber with MC of 15% or less.
Following these guidelines will result in solid, sturdy framing that meets code requirements. Don’t cut corners on the structural framing lumber!
Treated Dimensional Lumber
For applications where the wood will be exposed to moisture and outdoor elements, building codes require the use of treated lumber. Treatment infuses chemicals into the wood to help protect against rot, fungal decay, and insect damage.
Common scenarios where treated lumber should be used:
- Deck framing
- Porch framing
- Railings and posts
- Fences
- Landscape structures
- Sill plates
Treated lumber has a greenish tint or may show evidence of the incising or stamping associated with the treatment process. It’s best to use treated lumber that is dried after treatment (KDAT) for maximum stability.
Make sure all cuts, notches, or borings are field treated with an end-cut preservative to maintain the integrity of the treatment chemicals. Use hot-dipped galvanized or other corrosion-resistant hardware in conjunction with treated lumber.
Sizing Lumber for Beams and Headers
Dimensional lumber can be used as horizontal beam and header members to provide structural support in framing. This includes:
- Headers above doors and windows
- Floor beams
- Deck and porch beams
- Lintels
Sizing these horizontal members properly is key. Several factors affect the required size:
- Span – The distance between supports. Longer spans need bigger members.
- Loading – Will the beam carry a floor, roof, or just a wall? More weight needs more capacity.
- Species – Some wood species are naturally stronger than others.
- Grade – Higher lumber grades have higher allowable stress values.
- Time – Gradual long-term wood creep can occur and must be accounted for.
Consult structural engineering tables to determine the proper dimensional lumber size and grade to use for each beam or header application. Alternatively, use multiple members together to provide sufficient capacity.
Dimensional Lumber for Blocking and Bracing
In additional to framing, dimensional lumber plays a key role in providing blocking and bracing:
Blocking – Short lumber pieces installed between studs or rafters to strengthen the framing, provide attachment points for finishes, and transfer lateral loads. Common blocking applications include:
- Between ceiling joists along exterior walls to attach roof sheathing
- Between rafters or trusses to anchor the roof to walls
- Between studs to support shelving, railings,grab bars, or cabinets.
Bracing – Installed diagonally to resist lateral movement from wind forces. Some examples are:
- Knee braces at corners in attic spaces
- Let-in bracing at mid-height on exterior walls
- Diagonal deck framing immediately under the floor
Use 2×6 or 2×8 lumber for these important but often overlooked structural components. Don’t forget to properly nail and secure blocking and bracing.
Dimensional Lumber for Subfloors and Wall Sheathing
Sturdy subflooring and wall sheathing are essential parts of a building structure. They stiffen the overall framework, provide a nailing base, and tie all the framing elements together.
Plywood and OSB panels have largely replaced dimensional lumber sheathing, but it is still used in some circumstances:
Subflooring – Dimensional boards make a sturdy subfloor when topped with underlayment and finished flooring. Use 1×6 or 2×6 boards.
Wall sheathing – Horizontal 1×4 lumber installed diagonally can serve as exterior wall sheathing. Provides an old-fashioned ship-lap look.
Patterned looks – Some designers use dimensional lumber creatively to achieve special decorative sheathing patterns.
When using dimensional lumber for sheathing:
- Check moisture content – boards should be dried to 12% MC or less to avoid shrinkage.
- Allow 1/8″ gaps between boards for expansion.
- Stagger end joints between rows and nail every 12″ along edges.
- Use joist tape or blocking at all board edges for maximum rigidity.
Using Dimensional Lumber for Stairs
Dimensional lumber’s uniformity and availability makes it a natural choice for building stair components:
Stringers – These support the stair treads and are subjected to tension and compression. 2x12s are typical, but the required size depends on the span, height, and loading.
Treads – These horizontal boards need to withstand foot traffic and remain rigid. Standard 2x lumber like 2×6, 2×8, 2×10 provides good options.
Risers – Vertical boards enclosing the space beneath the treads. 1×6 or 1×8 boards are commonly used.
Railings / balusters – 2×2 or 2×4 lumber provides traditional railing parts, though metal elements are also popular.
Proper assembly and rigorous attachment of all stair components is crucial for safety and longevity. Construction adhesive and supporting metal angles or wooden kneewalls help strengthen stair framing.
Unique Dimensional Lumber Applications
While framing represents the bulk of its use, dimensional lumber can serve other unique roles:
- Garden boxes – Simple enclosed boxes for raised garden beds are easy to build from 2x lumber. Use treated wood or a plastic liner.
- Compost bins – Create three or four sided bins for composting using 2×4 or 2×6 lumber. Include removable front planks for easy access.
- Outdoor planters – Decorate decks, patios, or porches with dimensional lumber planter boxes. Vary depths and finishing for custom appeal.
- Benches – From simple 2×4 shop benches to elegant 2×6 deck seating, dimensional boards make sturdy legs and supports for benches.
- Signs and displays – Frame trade show booths, point-of-purchase displays, or outdoor business signs using dimensional lumber.
With proper planning and protection, dimensional lumber provides a versatile material for all types of building and remodeling applications.
Dimensional Lumber for Interior Finishing
Besides framing, dimensional lumber has some specialized uses for interior finishing as well. Its uniformity makes it perfect for situations where consistency and straight edges are preferable.
Door/window casings – Dimensions of 1x4s, 1x6s, and 1x8s allow attractive window and door trim. Upgraded appearance from standard Colonial or ranch trim profiles.
Chair rails – Horizontal trim piece provides elegant transition between upper and lower wall finishes. 1x4s or 1x6s offer classical chair rail dimensions.
Wainscoting – Dimensional lumber applied vertically with joints creates the paneled look of formal wainscoting. V-groove joints or decorative molding provide enhanced details.
Fireplace mantels – Mantels made from 1×6, 1×8, or mixed size dimensional lumber creates sturdy, rustic shelf with clean lines well-suited for many room decors.
Ceiling beams – Exposed 1x8s, 1x10s, or 1x12s serve as decorative faux beams. Space boards 2″ to 6″ apart for open look. Provides visual interest without bulky dimensions of real beams.
With attention to detail in material selection, joints, and finishes, dimensional lumber brings authenticity and custom appeal to interior spaces.
Working With and Installing Dimensional Lumber
Proper handling, cutting, and fastening ensures dimensional lumber performs as expected:
- Carry multiple boards vertically to avoid excessive bending stress. Don’t lift boards in the middle.
- Use sharp blades and cut lumber on proper supports to avoid splintering. Make curved cuts before installation.
- Pre-drill holes slightly smaller than fastener size when nailing or screwing near edges or ends of boards.
- Use nail sizes of at least 2.5x lumber thickness for maximum holding power. Increase nail length for end grain nailing.
- Countersink all nails and fill holes for best appearance on exposed dimensional lumber. Consider using trim-head screws.
- Allow 1/8″ gap between adjoining lumber pieces to accommodate any shrinkage that occurs as wood dries further.
- Attach dimensional lumber securely with adequate numbers of fasteners to carry all expected structural loads.
Following basic carpentry best practices makes dimensional lumber easier to work with and provides superior finished results. Consult local codes for any specific fastening or installation requirements.
Common Questions About Dimensional Lumber
What size dimensional lumber should be used for deck joists?
For deck joists, it is recommended to use 2×8 or larger dimensional lumber set on-center spacing of 16″ or less. This provides adequate stiffness and helps minimize bounce. 2x10s or 2x12s may be needed for longer joist spans.
What dimensional lumber is required for an exterior load-bearing wall?
Load-bearing exterior walls framed with dimensional lumber generally require 2×6 studs at 16″ on-center or 2x4s at 12″ on-center. Use No. 2 grade or better lumbers for durability. Higher 2×6 or 2×8 studs help meet insulation needs.
Is it okay to use dimensional lumber that is slightly warped or crooked?
Significant warping, twisting, bowing or crowning indicates the lumber is too wet or dried improperly after treatment. Stick with dimensional lumber that is straight and true for the best structural integrity and appearance.
Can treated and untreated dimensional lumber be used together in a project?
It’s best practice to use either all treated or all untreated lumber in a given project. Combining these can cause uneven shrinkage. Only use treated lumber in approved chemical formulations for indoor uses.
What is the strongest type of dimensional lumber?
Southern yellow pine lumber has among the highest strength properties of common dimensional lumber species. Douglas fir also provides excellent strength. Choosing a higher grade select structural lumber maximizes strength capabilities.
Key Takeaways on Dimensional Lumber
- Dimensional lumber provides standardized sizing that makes construction faster and simpler. Actual sizes are slightly smaller than nominal sizes.
- Match the proper dimensional lumber size and grade to each structural application for optimal strength and performance.
- For critical structural uses, choose quality load-bearing grades over low-cost lumber with more defects. Don’t cut corners on framing lumber.
- Use treated lumber where required by code for all exterior uses and wet environments to prevent rot and insect damage.
- Allow dimensional lumber to acclimate to intended indoor moisture conditions before use to prevent shrinkage issues after installation.
- Follow good carpentry practices for handling, cutting, and fastening dimensional lumber for maximum endurance. Use adequate numbers of nails and screws.
- Dimensional lumber has many specialized uses beyond framing, from furniture to decor. Pick lumber sizes and grades suited for each purpose.
With its versatility, strength, and standardized sizing, quality dimensional lumber is a smart choice as a primary building and remodeling material for both structural and decorative applications. Carefully selecting and installing dimension lumber will lead to sturdy results that stand the test of time.