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I am replacing a wooden deck with wrought iron posts and railings. The current beams are 4x8x8, but the wrought iron rails are welded in too close to the beam top for me to remove the beams without cutting them. (The wrought iron was added after the deck was built. I can cut the beams to remove them, no problem, but I won't have room to be able to angle in a replacement 4x8 beam.

  1. Would it be OK to instead use two 4x4 beams, one on top of the other? It looks like I have enough clearance to slide those into the beam hangers under the iron rails.
  2. If it is OK to use the two 4x4s, what you you recommend for how I connect the two beams to each other?
  3. Would I need to handle putting joist hangers onto the stacked beams in a particular way?

Thank you in advance.

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    A pair of vertically stacked 4x4s does not give you the same strength as a single vertically oriented 4x8. Horizontal would probably come close, but not vertical.
    – brhans
    Dec 7, 2021 at 19:38
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    A photo showing the problem areas would help here. Please edit the post and insert a photo, or upload the photo to an image-sharing site and post the link to it and someone will edit it inline for you.
    – Fredric Shope
    Dec 7, 2021 at 22:06
  • Can you provide a photo to show the problem with the wrought iron railing? Is that you want to keep it in place while replacing the beam?
    – r13
    Dec 7, 2021 at 23:38
  • Since iron welds nicely, you might consider making neat cuts into the wrought iron to remove it, rebuild the deck with the proper materials, then have someone weld the wrought iron back together for you. I'd consult with your welder on where to cut the metal to minimize the appearance of the seams when it's reassembled, and to ensure (s)he can do the welding in place when you're done.
    – FreeMan
    Dec 8, 2021 at 15:44
  • Thanks all for your comments and insights. Looks like I should get an iron worker to cut and reweld the rails and stay with 4x8 replacement beams. Thanks again!
    – D Gunther
    Dec 9, 2021 at 6:58

1 Answer 1

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No.

The dimensions and load capacity of lumber makes substitutions like this difficult.

A 4x8 is not equivalent to two 4x4s or two 2x8s. A 4x8 is actually closer to 3.5"x7.5". Stacked 4x4s would be 3.5"x7". Doubled 2x8s would be 3"x7.5".

Those dimensions matter for fittings like joist hangers, beam hangers or notches, and other things, but they also affect the strength and load capacity.

Disclaimer: It is possible to make substitutions in certain cases, but you must check and recheck all brackets, hangers and spaces to make sure they still fit with altered dimensions and check and recheck the load ratings of the substitute lumber. You can't count on near-dimension to have similar capacity and that means the original calculations have to be updated and approved. Some jurisdictions would require a permit for such an alteration, or at least a plan showing it still meets minimum requirements after substitution of lumber.

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