ud83dudcda Wood Deck Build Log u2014 25 of 45
u2190 Detail #9: Beam Strength Calc u00b7 Series Index u00b7 Detail #11: Purlin Strength Calc u2192
2026 Update from DIY Dad: Long Planning Period and Final Design Lock-Down
ud83duded2 RECOMMENDED PRODUCTS
Pressure-Treated Deck Lumber
Pressure-treated lumber is the baseline u2014 skip it and you’ll be rebuilding in 5 years.
The wood deck planning phase stretched over a long time. Actual construction didn’t start until about a year after the initial plan. During that time I revisited the design repeatedly, ending up with a much better result. ^ ^
Why Planning Took So Long
- Estimating material costs and adjusting the budget (hardwood is expensive)
- Design changes u2014 the roof shape changed from the original concept
- Difficulty carving out time while balancing work and childcare
- Additional decisions u2014 fence shape, stair placement
Taking time on the plan paid off in fewer construction mistakes. “Rush it and regret it” vs. “plan it thoroughly and build it right” u2014 that’s the DIY Dad style. m(_ _)m
How to Draw Plans
I drew my plans on graph paper with a pencil u2014 no CAD or specialist software. Drawing to accurate scale lets you catch clashes between members and joinery issues before they happen.
What to include in your drawings:
- Plan view (footing positions, decking direction)
- Elevation views (heights, railing, roof shape)
- Detail drawings (joint joinery)
- Materials list (member name, dimensions, quantity, species)
Using Excel or Google Sheets for the materials list makes quantity and cost calculations much easier. ^ ^
Rafter (u5782u6728) Strength Calculation
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. ^ ^
Today: rafter strength. The rafter calculation is a bit out of order here u2014 because the purlins (u6bcdu5c4b) sit on top of the rafters. I’m planning to use 1u00d74 lumber for the purlins to maximize the rafter span, which means the purlin will reach its strength limit before the rafter does. (Probably.) But first I’ll work out the span at which the rafter hits its limit.
Load conditions are the same as for the beam. Snow load: 2,569 N.
At minimum 4 rafters are needed, so each carries 1/3 of the total load.
u2191 Rafter layout
Treating as uniformly distributed load:
u03c9 = 2,569 / (3 u00d7 2,000) = 0.428 N/mm
Clear span L = 2,000 mm
M = u03c9Lu00b2 / 8 = 0.428 u00d7 2,000u00b2 / 8 = 214,000 Nu00b7mm
u03c3 = M / Z = 214,000 / 2,990 = 71.6 N/mmu00b2 < 157 N/mmu00b2 u2192 OK
u03b4 = 5u03c9Lu2074 / (384EI) = 5 u00d7 0.428 u00d7 2,000u2074 / (384 u00d7 2.05u00d710u2075 u00d7 72,600) = 6.6 mm < 6.7 mm (L/300) u2192 OK
Both stress and deflection are within allowable limits. ^ ^
Next up: the purlins.
That’s all for today! (^^)/~~~
ud83dudcda Wood Deck Build Log u2014 25 of 45
u2190 Detail #9: Beam Strength Calc u00b7 Series Index u00b7 Detail #11: Purlin Strength 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
