Wood as a Building Material

Wood as a Building Material

• A natural and renewable resource used in construction for centuries, wood is lightweight, strong, and workable.
• It is ideal for structural and finishing applications.

Wood Properties

Tree Growth and Structure

• Softwoods come from coniferous trees like pine, spruce, fir, and cedar, while hardwoods come from deciduous trees like oak, maple, cherry, and walnut.
• Wood consists of alternating bands of earlywood (spring growth) and latewood (summer growth), affecting density and strength.
• Heartwood is the inner, denser, durable portion, and sapwood is the outer, lighter layer that transports water.

Moisture Content and Dimensional Stability

• Wood is hygroscopic and absorbs/releases moisture based on environmental humidity.
• Equilibrium Moisture Content (EMC) is when wood is neither gaining nor losing moisture.
• Shrinkage and expansion are greatest across the tangential plane (parallel to growth rings) and least along the longitudinal axis (length of tree).
• Seasoning or drying of wood can be done via air-drying, which is slow but energy-efficient or kiln-drying, which is faster and controlled but requires energy.
• Green lumber has high moisture content, leading to greater shrinkage, while kiln-dried lumber is more stable.

Strength Properties of Wood

• Modulus of Elasticity (MOE) measures stiffness, and Modulus of Rupture (MOR) measures breaking strength.
• Compression strength is higher along the grain than across the grain.
• Tensile strength is excellent along the grain but weak perpendicular to it.

Wood Processing and Grading

Lumber Manufacturing

• Logs are cut into different grain orientations, including plain-sawn (most common, prone to warping), quarter-sawn (more stable but wasteful/expensive), and rift-sawn (extremely stable, used in fine woodworking).

Lumber Grading

• Structural grading determines load-bearing capacity (e.g., Select Structural, No. 1, No. 2), and appearance grading is used for finish lumber (e.g., Select A, B, C, D).
• A 2x4 is actually 1.5” x 3.5”.

Engineered Wood Products

• Plywood uses cross-laminated veneers for strength.
• Oriented Strand Board (OSB) is made of compressed wood strands.
• Glued Laminated Timber (Glulam) are large structural beams of glued wood layers.
• Laminated Veneer Lumber (LVL) is stronger and more uniform than standard lumber.
• Cross-Laminated Timber (CLT) is a mass timber alternative useful for large structures.

Wood Protection & Preservation

• Chemical treatments protect against decay and termites.
• Fire retardants reduce flammability.
• Weatherproofing coatings and sealants prevent moisture absorption.

Wood Light Frame Construction

History and Evolution

• Balloon framing was used in the 19th century but discontinued due to fire risk.
• Platform framing, where each floor is framed separately, is the modern standard.

Components of Light Frame Construction

Foundation System

• Concrete slab-on-grade or raised foundation with stem walls are typical.
• Sill plates are anchored with bolts to prevent movement.

Floor Framing

• Joists (2x10 or 2x12) span between beams and walls.
• Bridging improves stiffness and reduces bounce.
• Subflooring materials like plywood or OSB are nailed/glued to joists.

Wall Framing

• Studs are vertical members, usually 2x4 or 2x6.
• Top and bottom plates are horizontal members that secure studs.
• Sheathing such as OSB or plywood provides lateral stability.

Roof Framing

• Rafters are sloped structural members that support the roof.
• Ceiling joists support the ceiling.
• Trusses are pre-manufactured assemblies that replace rafters for efficiency.

Framing Connections

• Nails, screws, and bolts are used to fasten members.
• Metal connectors and brackets improve earthquake and hurricane resistance.

Fire and Moisture Protection

• Fireblocking prevents vertical fire spread.
• Flashing and weather barriers prevent water infiltration.

Sustainability in Light Frame Construction

• Advanced framing reduces wood waste and improves insulation efficiency.
• Prefabricated components increases speed and reduces material waste.

Stone and Concrete Masonry

Stone Masonry

Types of Stone

• Granite is hard and durable.
• Limestone is softer and easily shaped.
• Sandstone is common in historic buildings.
• Marble is used for decorative finishes.

Stone Masonry Techniques

• Ashlar masonry uses precisely cut stones.
• Rubble masonry uses randomly shaped stones.
• Coursed masonry is layered horizontally.

Concrete Masonry Units (CMUs)

• CMUs are manufactured from cement, sand, and aggregate, all mixed and steam-cured.
• The standard size is 8”x8”x16”.
• Hollow blocks allow for rebar placement.

Masonry Wall Construction

• Loadbearing walls carry structural loads.
• Cavity walls improve insulation and drainage.
• Reinforced masonry has steel bars embedded for strength.

Sustainability in Masonry

• Recycled content, such as fly ash, can be used in concrete.
• Masonry requires minimal maintenance, increasing its longevity.