ud83dudcda Wood Deck Build Log u2014 18 of 45
u2190 Detail #2: Structural Framing Sketches u00b7 Series Index u00b7 Detail #4: Main Beam First Calc u2192
2026 Update from DIY Dad: Detailed Planning and Construction Prep
ud83duded2 RECOMMENDED PRODUCTS
Pressure-Treated Deck Lumber
Pressure-treated lumber is the baseline u2014 skip it and you’ll be rebuilding in 5 years.
Once the overall structure was settled, the work shifted to joint details and the materials list. Thinking this through carefully before construction made the build go smoothly. m(_ _)m
Main Beam (u5927u5f15) Calculation Setup
ud83duded2 RECOMMENDED PRODUCTS
Deck Stains & Waterproof Sealers
Stain every 2u20133 years. It’s the single cheapest way to double deck lifespan.
Hi, I’m DIY Dad. ^ ^
Now let’s plan the sub-structure under the deck floor: posts (u675fu67f1), main beams (u5927u5f15), and floor joists (u6839u592a). Starting with the posts.
For this footprint, I think 4 posts will work as a starting point, even if the beams probably won’t meet strength requirements. Let me try the minimum-cost layout first.
u2191 Column layout u2014 4 posts
Blue lines = posts, red lines = main beams (u5927u5f15).
I’ll treat the beam as a simply supported beam with a concentrated load at mid-span.
u2191 Simply supported beam diagram
Load Assumption
Imagine DIY Dad standing on the deck while lifting his young child u2014 roughly 80 kg combined. Walking dynamically, that’s about 3u00d7 the static load, giving a 240 kg concentrated load.
Treated as a short-term load. Two beams share the load, so each carries 1/2. For safety I’m assuming the worst case: concentrated load at mid-span.
Clear span L = column-to-column distance = 3.7 m (3,700 mm).
u2191 Concentrated load diagram
Material Properties u2014 Super Light 700 Steel Tube
- Section modulus Z = 2,990 mmu00b3
- Second moment of area I = 72,600 mmu2074
- Modulus of elasticity E (SS400 mild steel) = 2.05 u00d7 10u2075 N/mmu00b2
- Long-term allowable stress = 157 N/mmu00b2
- Short-term allowable stress = 235 N/mmu00b2
- Allowable deflection = L / 300
All parameters are ready. ^ ^ Let’s calculate in the next article!
That’s all for today! (^^)/~~~
ud83dudcda Wood Deck Build Log u2014 18 of 45
u2190 Detail #2: Structural Framing Sketches u00b7 Series Index u00b7 Detail #4: Main Beam First Calc 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
