ud83dudcda Wood Deck Build Log u2014 15 of 45
u2190 Structural Design Pt.3: Corrugated Roof u00b7 Series Index u00b7 Detail #1: Installation Space Planning u2192
→ See the complete Wood Deck DIY Guide
2026 Note from DIY Dad: Structural Design Overview
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Pressure-Treated Deck Lumber
Pressure-treated lumber is the baseline u2014 skip it and you’ll be rebuilding in 5 years.
Once the materials were chosen, the next step is structural design — deciding what structure to build, how to detail the roof, what to do about the railing, working it all out by drawing plans.
Basic Structure of a Wood Deck
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Deck Stains & Waterproof Sealers
Stain every 2u20133 years. It’s the single cheapest way to double deck lifespan.
A wood deck is built in layers: footing (束石) → post (束柱) → beam (大引き) → floor joist (根太) → decking board.
- Footing (束石 tsuka-ishi): placed on the ground as a foundation — concrete block or pre-cast footing
- Post (束柱 tsuka-bashira): stands on the footing
- Beam (大引き ŏ-biki): laid across the posts along the long axis
- Floor joist (根太 neda): laid across the beams along the short axis, supporting the decking
- Decking board: surface material nailed onto the joists
How to Work Through the Structural Design
- Measure the installation space precisely (width, depth, floor height)
- Decide the deck surface height (align with the sash door threshold)
- Lay out footing positions (target span 900–1200 mm)
- Calculate beam and joist sizes and counts
- Calculate the number of decking boards and gaps (3–5 mm gaps)
- Create the materials list and get a cost estimate
If the span between supports is too wide the decking boards will deflect. Choose the right span based on board thickness and species.
Roof Detail Design
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Deck Screws & Fasteners
Use stainless screws only u2014 standard screws rust and stain the deck within one rainy season.
When adding a roof to a wood deck, the interface with the building is the biggest design challenge.
- Fix to building exterior wall — most common and robust
- Free-standing structure — no attachment to the building
- Extend existing eave or overhang
For a rental property, drilling into the exterior wall requires later patching. I chose a free-standing structure to allow full restoration.
Railing and Fence Design
When the deck is 30 cm or more above ground, consider installing a railing for safety. I planned a fence-style railing serving both as privacy screening and safety, using the same decking board material for a consistent look.
Originally published: 2017-05-30. It turned out that corrugated roofing and Super Light 700 are a poor match. Super Light 700 is too strong — to restore structural balance the roof substrate needed a weaker material. The conventional substrate for corrugated roofing is wood. SPF works well as a purlin (母屋) material while providing a softer substrate that accepts the corrugated roofing fasteners. The connection between polycarbonate corrugated roofing and SPF uses dedicated roofing nails — stainless steel screw nails:
↑ Stainless steel screw nails
These cost far less than the pipe bolt set option. A pack of 90 nails (9 rows × 10 strips) is ¥980. For the full roof area: 450/90 × 980 = ¥4,900. That works!
With this, all materials were finalized:
- Decking material: SPF
- Structural frame: Super Light 700 steel pipe
- Roofing: polycarbonate corrugated roofing
- Roof purlin (母屋): SPF
ud83dudcda Wood Deck Build Log u2014 15 of 45
u2190 Structural Design Pt.3: Corrugated Roof u00b7 Series Index u00b7 Detail #1: Installation Space Planning u2192
DIY Renovation Quote Review Manual
How to read, compare, and negotiate contractor quotes. This manual saved me u00a5800,000 on a single renovation project.
ud83cudfe0 More from DIY Father
15 years of landlord experience u00b7 3 apartment buildings u00b7 DIY renovations that saved millions of yen. Browse all articles at diytosan.com
