Calculate lumber, posts, beams, rafters, hardware, and concrete needed to build your pergola
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Quality hardware and accessories for your pergola project
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Pergola posts should be set in concrete footings that extend below the frost line, typically 24-48 inches deep depending on your climate zone. In warmer climates, 24 inches is often sufficient, while cold climates may require 36-48 inches. The footing diameter should be at least 3 times the post width - so 12 inches minimum for a 4x4 post and 18 inches for a 6x6 post. Use a post base or bracket to keep the bottom of the wood post above the concrete surface to prevent rot.
For pergolas up to 10 feet wide, 4x4 posts are typically adequate. For spans over 10 feet or pergolas over 10 feet tall, 6x6 posts provide better structural support and visual proportion. 6x6 posts are also recommended if you plan to hang heavy items like swings or if your area experiences high winds. From a purely aesthetic standpoint, 6x6 posts look more substantial and balanced with larger pergolas.
Pergola rafters are typically spaced 12-24 inches apart. Closer spacing (12 inches) provides more shade and a fuller look, while wider spacing (24 inches) creates a more open, airy feel. For 2x6 rafters spanning up to 10 feet, 16-inch spacing is a good balance between shade and openness. For longer spans, use 2x8 rafters or consider closer spacing for additional structural support.
Pressure-treated lumber is the most economical choice and lasts 15-20 years with proper maintenance. Cedar and redwood are naturally rot-resistant, beautiful, and last 20-25 years but cost 2-3x more than pressure-treated. For the longest lifespan (25+ years), consider tropical hardwoods like ipe or composite/vinyl materials. Always use exterior-rated stainless steel or hot-dipped galvanized hardware regardless of wood choice to prevent corrosion and staining.
Yes, attached pergolas (also called lean-to pergolas) connect to your house using a ledger board, similar to deck construction. The ledger must be properly flashed to prevent water intrusion and attached to wall framing or rim joist (not just siding) using lag bolts or through-bolts. This design requires only 2 posts instead of 4, reducing material costs. However, check local building codes as permits are often required for attached structures, and improper installation can cause water damage to your home.
Each pergola post footing typically requires 1-2 bags of concrete (60-80 lb bags) depending on the hole size and depth. For a standard 12-inch diameter hole that is 30 inches deep, you will need approximately 1.5 to 2 bags per post. Larger 6x6 posts with 18-inch diameter holes may require 3-4 bags per footing. Mix concrete to a thick, not soupy, consistency and slope the top away from the post to shed water.