Best way to implement a load bearing post

[RaceDiagnostics]

I'm replacing this 200mm by 130mm post that supports the roof of the garage.

I can either build it out of 4 lengths of say 45 x 145mm timber screwed together or one solid piece of Douglas fir that a local wood mill said they would cut for me. The new one will have a metal footing to prevent rot.

Any thoughts on which option is the best engineering solution.

 

[Bornfree]

I bet this ends up with someone suggesting a 356x406x551 universal column.

 

[brightspark]

steel square box clad with wood

 

[RaceDiagnostics]

I asked chat gpt.

The decision on whether to use 4 lengths of 45mm x 145mm timber screwed together or one solid piece of Douglas Fir for your 190mm x 135mm timber load-bearing post depends on several factors such as structural integrity, ease of construction, and material characteristics. Here’s a breakdown of both options:

1. 4 lengths of 45mm x 145mm timber screwed together:​

• Advantages:
  • Availability of Materials: It's easier to source standard sizes of timber (45mm x 145mm) and then combine them to create the desired cross-section.
  • Potential for Fewer Defects: If each piece is individually chosen for minimal defects (e.g., knots or twists), combining them could reduce the chance of one large piece of timber having significant defects.
  • Easier to Handle: Four smaller pieces may be easier to manage and transport, especially if you are working with large sections.
  • Flexibility: You can potentially replace individual pieces if they become damaged in the future.
• Disadvantages:
  • Complexity of Construction: Screwing the timbers together requires precision to ensure they align properly. Misalignment can cause weakness at the joints or in the post overall.
  • Joint Durability: The screws or bolts used to hold the pieces together may degrade over time due to moisture, and if not properly treated, the joints could weaken.
  • Potential for Movement: Even with screws, the pieces could expand or contract at different rates due to changes in moisture content, leading to possible shifting or movement in the post.

2. One solid piece of Douglas Fir:​

• Advantages:
  • Higher Structural Integrity: A solid piece of timber, especially one of high-quality Douglas Fir, provides superior strength and stability compared to assembled pieces. The lack of joints ensures a continuous grain, which helps to handle load-bearing stress more effectively.
  • Fewer Points of Failure: There are no joints to fail, which could be a risk with the screwed-together option.
  • Aesthetic Appeal: A single, solid piece of timber has a more uniform appearance and is typically more aesthetically pleasing, especially in visible structural elements.
  • Less Movement: Solid timber will generally expand and contract more uniformly, reducing the risk of structural movement over time.
• Disadvantages:
  • Availability and Cost: Sourcing a single piece of Douglas Fir that fits the required dimensions (190mm x 135mm) can be challenging, especially if you need the piece to be free from defects. This could also be more expensive.
  • Handling and Transportation: A large, solid piece of timber is more difficult to transport and handle, especially if it's quite heavy.
  • Defects: If the piece of timber has any natural defects, like knots or twists, they will impact the entire post, whereas defects in the individual pieces of a built-up post might be isolated.

Recommendation:​

For structural strength and stability, using one solid piece of Douglas Fir is generally the better choice for a load-bearing post. It will offer superior strength, fewer potential points of failure, and better long-term durability. However, you need to ensure that you can source a defect-free piece that is large enough, and be prepared for the challenges of handling and cost.


If sourcing a large solid piece of timber is difficult, and you're willing to take extra precautions with the joints, the 4 lengths of 45mm x 145mm timber could be a viable alternative. Ensure that you properly align the timbers, use high-quality screws or bolts, and treat the joints for moisture resistance to minimize potential weaknesses.

 

[RaceDiagnostics]

steel square box clad with wood

Too much effort for my limited woodworking skills.

 

[RichardM]

Steel box painted white to match the old upright.

 

[iNf]

I can either build it out of 4 lengths of say 45 x 145mm timber screwed together or one solid piece of Douglas fir

Or use a glulam beam/post if you can find one in a size that suits, would be a lot easier /stronger than screwing multiple lengths of timber together and less hassle now and down the line than a single piece of wood that is likely to move.

 

[roofman]

100mm X 100mm steel box plated top and bottom.

 

[RaceDiagnostics]

For all you "steel posters", how about just timber cladding one of the acrows.

 

[brightspark]

steel box and scaffie planks cut down are cheap enough and a good size

 

[Barking Mat]

I was thinking some kind of concrete - rebar thing myself.

 

[RaceDiagnostics]

Just looked up the price of 100mm by 5mm box section, would be more than £100 delivered.

 

[Barking Mat]

Why replace it ? Looks o.k. from here.

 

[RaceDiagnostics]

I was thinking some kind of concrete - rebar thing myself.

The old one is made out of rafters screwed together and has lasted 40 years plus. I'm looking for a quick and easy solution.

 

[RaceDiagnostics]

Why replace it ? Looks o.k. from here.

It's no longer attached to the ground.

 

[Barking Mat]

Steel, concrete or wood, your choice.

Or reinforced pasta cheese ?

 

[RaceDiagnostics]

Or use a glulam beam/post if you can find one in a size that suits, would be a lot easier /stronger than screwing multiple lengths of timber together and less hassle now and down the line than a single piece of wood that is likely to move.

No one supplying anything like that locally but looks good if you can get it.

 

[Barking Mat]

Cut off six or twelve inches, graft in a new bit with wedges ?

 

[RaceDiagnostics]

Cut off six or twelve inches, graft in a new bit with wedges ?

Thought about that too, but I'm no joiner and would end up bodging it. I'm thinking one new single piece will be easiest.

 

[Misterg]

I can either build it out of 4 lengths of say 45 x 145mm timber screwed together or one solid piece of Douglas fir that a local wood mill said they would cut for me. [...]

Any thoughts on which option is the best engineering solution.

Single piece - less chance of buckling.

If you made it of 4 pieces they would need to be fastened together at fairly close intervals (or glued) so that they act as one piece.