ud83dudcda Wood Deck DIY Guide u2014 5 of 11
u2190 No.6: Floor Material u2014 Why SPF? u00b7 Series Index u00b7 No.7: Choosing Structural Members u2192
- Introduction
- Why People Tend to Get Structural Member Selection Wrong
- What to Decide Before Choosing Materials
- The Reality of an All-Lumber Design
- Steel Pipe as an Option
- Why Not Use Steel Pipe for Everything?
- The Optimal Answer: Division of Roles
- Structural Calculations as “Validation of the Choice”
- What Matters Most in Structural Member Selection
- Conclusion: In DIY, “Can You Use It with Confidence?” Is Everything
- Next Article
Introduction
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For most people building a wood deck, the biggest source of confusion is material selection.
- Which lumber species should I use?
- How thick does it need to be?
- Is steel pipe actually a valid option?
- Do I really need to do structural calculations?
This article organizes u2014 based on 6+ years of real use u2014 what structural members to realistically choose for a DIY deck, including:
- Why the decision is so confusing
- What criteria were used to judge
- What happened after actually using it
Why People Tend to Get Structural Member Selection Wrong
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Most mistakes fall into one of these patterns:
- The assumption that “bigger means safer”
- Prioritizing looks and treating structure as an afterthought
- Copying professional specs directly without adaptation
- Avoiding structural questions because they seem too complicated
In DIY especially, anxiety tends to push people toward “make it thicker” u2014 but that often leads to:
- Higher cost
- More difficult cutting and shaping
- Reduced installation precision
What to Decide Before Choosing Materials
Before settling on materials, there are essential questions to answer:
- Where will the load be applied?
- Is the load dynamic (moving) or static?
- How will conditions change over the long term?
For this deck, the anticipated loads included:
- Adults walking across it
- Children running on it
- A dog jumping around on it
- Snow accumulating on the roof
This is a combination of dynamic and long-term loads.
The Reality of an All-Lumber Design
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First, consider using only lumber for the structure.
Pros:
- Easy to work with
- Natural appearance
- Extensive DIY information available
Cons:
- Rots
- Warps
- Cracks
- Strength degrades over time
The problem areas are especially parts close to the ground and those used as primary structural members. Short-term, they may be fine u2014 but the risk factors multiply quickly at the 5- and 10-year marks.
Steel Pipe as an Option
This is how single-pipe scaffolding (Super Light 700) came up as a candidate. Honestly, at first the reaction was “steel pipe for a wood deck?” u2014 it felt wrong. But once the properties were laid out systematically:
- Excellent in compression and bending
- Consistent, predictable performance
- Does not rot
- Good availability
- Predictable cost
It became clear that it satisfies a remarkable number of DIY-relevant criteria.
Why Not Use Steel Pipe for Everything?
A common question at this point is: “Then why not use steel pipe for everything?”
The answer is: no. The reasons:
- Feel underfoot when walking
- Freedom to cut and shape custom lengths and angles
- Appearance
- Ease of replacing individual sections
If the floor and finishing surfaces were also steel pipe:
- Cold to the touch
- Slippery
- An overwhelmingly industrial look
…the result is a deck that is genuinely unpleasant to use.
The Optimal Answer: Division of Roles
The conclusion for this deck:
- Structural skeleton: steel pipe
- Surfaces people contact directly: lumber (SPF)
Steel pipe handles: strength, stability, and long service life. Lumber handles: texture, appearance, and workability. Use only the strengths of each material u2014 that is the optimal approach for DIY.
Structural Calculations as “Validation of the Choice”
DIY Dad performed simplified structural calculations for all members: columns, joists, floor beams, and rafters. The goal was:
- Eliminate dangerous design choices
- Avoid making decisions purely on gut feeling
The purpose is not “I calculated it, therefore it is safe” u2014 rather, “I calculated it and avoided the bad designs.”
What Matters Most in Structural Member Selection
Ultimately, what matters most is:
- Not searching for a single “right answer”
- Choosing the solution that fits your specific conditions
In DIY, the optimal solution is one that satisfies these three conditions:
- You can build it yourself
- You can maintain it yourself
- It doesn’t feel unsafe
Conclusion: In DIY, “Can You Use It with Confidence?” Is Everything
More than 6 years after completion, this deck still has:
- No deflection
- No unusual sounds
- No sense of unease
That is because, at the material selection stage, choices were made that were neither excessive nor inadequate.
Next Article
NO.8 | Material Comparison: SPF Lumber vs. Super Light 700
- What the real-world differences turned out to be
- What each is suited to and not suited to
- How to use each in a DIY context
That’s all for today u2014 see you in the next article!
ud83dudcda Wood Deck DIY Guide u2014 5 of 11
u2190 No.6: Floor Material u2014 Why SPF? u00b7 Series Index u00b7 No.7: Choosing Structural Members 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
