Decking Calculator

Decking is the flat, load-bearing surface of an outdoor platform, porch, or rooftop patio: the finished walking surface of wood, composite, or PVC boards fastened to the joists and beams beneath it.

The 3/4/5 rule is a geometric layout method based on the Pythagorean theorem (3² + 4² = 5²) used to ensure deck corners and ledger connections form perfect 90-degree right angles. Measure 3 feet along one framing side, 4 feet along the perpendicular side, and adjust the angle until the diagonal span between points measures exactly 5 feet (or 6/8/10 ft for larger decks).

The main types of decking are: (1) Pressure-Treated Softwood (economical pine/fir treated against rot), (2) Natural Hardwoods (dense exotic woods like Ipe, Cumaru, and Tigerwood), (3) Natural Softwoods (Cedar and Redwood), (4) Wood-Plastic Composite (Trex, Fiberon, TimberTech made from recycled polymers and wood fiber), (5) Capped Cellular PVC (100% synthetic, moisture-proof boards like Azek), and (6) Aluminum Decking.

The purpose of decking is to create a level, safe, elevated or ground-level outdoor living space for relaxation, dining, and entertaining that bridges indoor and outdoor environments. Decking is also ideal for uneven slopes, second-story access, and poolside areas where pouring concrete slabs is impractical or costly.

Standard slatted decking is water-resistant rather than waterproof, because rainwater freely drains through the 1/8 to 1/4 inch gaps between boards. While composite and PVC boards do not absorb water, the substructure beneath remains wet unless an under-deck drainage trough system (such as Trex RainEscape) is installed.

Decking is also called deck boards, deck planks, outdoor flooring, patio decking, or deck surfacing.

For natural wood decking, the best waterproofing is a high-grade penetrating oil-based exterior stain and sealer with UV inhibitors and mildewcides. For structural substructures, self-adhering butyl joist tape applied over joist tops is the best moisture barrier. For creating dry usable space underneath elevated decks, an under-joist membrane drainage system is the gold standard.

The best alternatives to decking are: (1) Concrete or Stone Paver Patios (virtually zero maintenance, rot-proof, 50+ year lifespan), (2) Stamped or Poured Concrete Patios (durable and budget-friendly), (3) Porcelain Outdoor Tiles (scratch-proof, stain-proof, modern), (4) Crushed Stone or Pea Gravel Patios (inexpensive, permeable drainage), and (5) Natural Flagstone terraces.

Composite decking is an engineered building material made from a combination of recycled wood fibers (sawdust) and recycled plastic polymers (polyethylene or polypropylene), blended with bonding agents and color pigments. Most modern composite boards are "capped" with a tough polymer shell that resists stains, fading, scratches, rot, and insect damage without staining or painting.

Cut composite decking using a standard circular saw, miter saw, or table saw equipped with a sharp carbide-tipped blade (preferably 60-tooth to 80-tooth on 10" or 12" miter saws, or dedicated composite blades). Cut smoothly and steadily to avoid melting the plastic core, support both ends of the board to prevent tear-out, and wear safety glasses and a dust mask.

You can paint older, uncapped first-generation composite decking using high-adhesion exterior acrylic latex deck paint after thorough cleaning and applying a specialty primer. However, painting modern capped composite decking (such as Trex Transcend) is not recommended because the protective polymer cap resists paint adhesion, leading to peeling, flaking, and voiding the manufacturer warranty.

Composite decking boards generally cost between $4 to $12 per linear foot ($8 to $22 per square foot for decking materials alone). A complete composite deck installed by a contractor (including footings, framing, railings, and hardware) typically ranges from $30 to $60+ per square foot ($12,000 to $25,000+ for a standard 400 sq ft deck), compared to $15 to $35/sq ft for pressure-treated wood.

To install composite decking: (1) Space joists at maximum 16" on-center (12" o.c. for diagonal patterns) and apply butyl joist tape; (2) Fasten starter clips along the perimeter; (3) Push the first grooved board into the starter clips; (4) Insert hidden fastener clips into the board groove at every joist intersection; (5) Slide the next board into the clips; (6) Maintain 3/16" to 1/4" side gaps and required end gaps for thermal movement; (7) Fasten edge and breaker boards with color-matched composite screws and plugs.

To install Trex decking: (1) Ensure joists are level and spaced 16" o.c. max (12" o.c. for 45° layouts); (2) Apply Trex Protect joist tape; (3) Fasten Trex Universal Starter Clips along the outside rim joist; (4) Slide the first grooved Trex board into the starter clips; (5) Insert Trex Hideaway Universal Fasteners into the inner groove at every joist; (6) Drive the fastener screws down snugly; (7) Slide subsequent boards into the clips and repeat across the deck; (8) Fasten the final board with color-matched face screws.

Clean Trex decking at least twice a year using warm soapy water (mild dish soap) and a soft-bristle nylon brush. Scrub along the grain of the boards to dislodge dirt, pollen, and debris, then rinse thoroughly with a garden hose. For grease, food, or oil spills, wash immediately with soap and water or a composite deck cleaner. Avoid harsh chlorine bleach or acetone.

No, you should not paint modern capped Trex decking. Trex boards feature a non-porous protective shell that repels moisture and stains, which also prevents paint from adhering properly. Painting Trex will cause flaking, blistering, constant maintenance, and will void your Trex 25-to-50-year fade and stain warranty.

Trex composite decking typically lasts 25 to 50 years or longer. Trex backs its products with extensive manufacturer residential warranties: 25 years for Trex Enhance, 35 years for Trex Select, and 50 years for premium Trex Transcend and Lineage collections against rotting, splintering, splitting, fading, and staining.

Trex decking boards range from: (1) Trex Enhance Basics: ~$2.50 to $4.00 per linear foot ($5–$8/sq ft), (2) Trex Select: ~$4.50 to $6.50 per linear foot ($9–$13/sq ft), and (3) Trex Transcend / Lineage: ~$7.50 to $11.00 per linear foot ($15–$22/sq ft for boards). A complete professionally installed Trex deck averages $35 to $65+ per square foot total.

Yes, you can pressure wash Trex decking safely if you follow manufacturer rules: use a pressure washer rated at 3,100 psi or lower, attach a wide 40-degree or 25-degree fan nozzle, keep the spray tip at least 8 to 12 inches away from the board surface, and spray in the direction of the grain. Never use a narrow pinpoint (0°) nozzle, as concentrated pressure will damage the composite cap.