Replacing lumber with equiv strength steel/aluminum. Sizing?

In summary, a building made of lumber would not be suitable for a greenhouse because the humidity would rapidly decay the wood. Steel and aluminum tubes can be used in place of lumber, and posts should be replaced with galvanized steel or aluminum tubing.
  • #1
Eciton
2
0
Hello, I'm in the design phase of a greenhouse building and am tossing around the idea of not using lumber. I have put up many stick built structures but am afraid the humidity will rapidly decay a conventional pine/fir. And I want to avoid pressure treated if possible

Based on a roofing rafter span table the 8-9' span of the glazed south wall is easily supported by 2x6 lumber on a 24" center. 2x8 would do it with plenty of room to spare, Can anyone point me to a comparable strength steel tube or aluminum tube? Locally I can get 2x2 galvanized steel tube with 1/8" wall thickness and 2x4" aluminum tube with 1/8" wall.

Also as a ridge beam I could easily use doubled up 2x12s. Locally I can get 4"x4" galv sq tube with 1/4" walls. Posts would normally be 6x6s. I would think the 4x4 galv steel should replace that with plenty to spare.

So structural members I want to replace...

Rafters 2x6 - 8' long span
Posts 6x6 - 8' heigh (3, one per 8' of width)
Ridge beam 2, 2x12s - 24' wide

As much as I have tried to find any equivalent chart comparing lumber to steel and aluminum tube I have fallen short

Thank you
 
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  • #2
Eciton said:
Hello, I'm in the design phase of a greenhouse building and am tossing around the idea of not using lumber. I have put up many stick built structures but am afraid the humidity will rapidly decay a conventional pine/fir. And I want to avoid pressure treated if possible

Based on a roofing rafter span table the 8-9' span of the glazed south wall is easily supported by 2x6 lumber on a 24" center. 2x8 would do it with plenty of room to spare, Can anyone point me to a comparable strength steel tube or aluminum tube? Locally I can get 2x2 galvanized steel tube with 1/8" wall thickness and 2x4" aluminum tube with 1/8" wall.

Also as a ridge beam I could easily use doubled up 2x12s. Locally I can get 4"x4" galv sq tube with 1/4" walls. Posts would normally be 6x6s. I would think the 4x4 galv steel should replace that with plenty to spare.

So structural members I want to replace...

Rafters 2x6 - 8' long span
Posts 6x6 - 8' heigh (3, one per 8' of width)
Ridge beam 2, 2x12s - 24' wide

As much as I have tried to find any equivalent chart comparing lumber to steel and aluminum tube I have fallen short

Thank you
So structures in the US need to be signed off by your local code enforcement folks (city or county). Have you asked them these questions? They are the ones who have to approve it.
 
  • #3
Not all structures do. This type in my area falls under agricultural use and has exemption. I did ask the county and the response was consult an engineer.

I wanted to design something with a decent degree of certainty that it would work before paying an engineers hourly rate to review

Thanks

berkeman said:
So structures in the US need to be signed off by your local code enforcement folks (city or county). Have you asked them these questions? They are the ones who have to approve it.
 
Last edited by a moderator:
  • #4
Eciton said:
I did ask the county and the response was consult an engineer.
We will give you the same advice. Thread is closed.
 

1. What are the benefits of replacing lumber with equivalent strength steel or aluminum?

Replacing lumber with equivalent strength steel or aluminum can bring several benefits, such as reducing the weight of the structure, increasing its durability and resistance to weather and pests, and allowing for more flexibility in design. It can also lead to cost savings in the long term due to reduced maintenance and replacement costs.

2. How do you determine the appropriate size of steel or aluminum to replace lumber in a structure?

The size of the steel or aluminum needed to replace lumber will depend on several factors, including the load-bearing requirements of the structure, the type of steel or aluminum being used, and the design of the structure. Structural engineers typically use mathematical calculations and computer simulations to determine the appropriate size for the steel or aluminum members.

3. Is it more expensive to replace lumber with equivalent strength steel or aluminum?

The initial cost of using steel or aluminum may be higher than using lumber. However, as mentioned before, the long-term cost savings in terms of reduced maintenance and replacement costs can outweigh the initial cost. Additionally, using steel or aluminum can lead to a more efficient and durable structure, which can save money in the long run.

4. Are there any limitations to replacing lumber with equivalent strength steel or aluminum?

While steel and aluminum have many advantages over lumber, there are some limitations to consider. For example, steel and aluminum can corrode if not properly coated or maintained, and they may require more specialized tools and techniques for construction. Additionally, the availability and cost of steel and aluminum may vary depending on location.

5. What are some common applications for replacing lumber with equivalent strength steel or aluminum?

Structures that require high strength and durability, such as bridges, high-rise buildings, and industrial facilities, often use steel or aluminum instead of lumber. Additionally, steel and aluminum are commonly used in building construction for elements such as beams, columns, and trusses. They can also be used in residential construction for roofing, siding, and framing.

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