ud83dudcda Wood Deck Build Log u2014 22 of 45
u2190 Detail #6: Main Beam Redesign (Revised) u00b7 Series Index u00b7 Detail #8: Decking Board Strength u2192
2026 Update from DIY Dad: Long Planning Period and Final Design Lock-Down
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Floor Joist (u6839u592a) Strength Calculation
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Hi, I’m DIY Dad. ^ ^
After the main beams (u5927u5f15), next up is the floor joists (u6839u592a), which sit on top of the beams.
u2191 Floor joist layout
Calculation
Clear span = beam-to-beam distance = 1.79 m (1,790 mm).
Design load: same 240 kg as used for the beams. However, the floor joists receive load through the decking boards u2014 at least 4 joists share it, so each joist carries 1/4.
W = 240 u00d7 (1/4) u00d7 9.8 = 588 N
M = WL / 4 = 588 u00d7 1,790 / 4 = 263,130 Nu00b7mm
u03c3 = M / Z = 263,130 / 2,990 = 88.0 N/mmu00b2 < 157 N/mmu00b2 u2192 OK
u03b4 = WLu00b3 / (48EI) = 588 u00d7 1,790u00b3 / (48 u00d7 2.06u00d710u2075 u00d7 72,600) = 4.72 mm < 5.97 mm (L/300) u2192 OK
Both stress and deflection are within allowable limits. ^ ^
Next up: the decking boards.
That’s all for today! (^^)/~~~
ud83dudcda Wood Deck Build Log u2014 22 of 45
u2190 Detail #6: Main Beam Redesign (Revised) u00b7 Series Index u00b7 Detail #8: Decking Board Strength u2192
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15 years of landlord experience u00b7 3 apartment buildings u00b7 DIY renovations that saved millions of yen. Browse all articles at diytosan.com
