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I am looking at finishing my basement under a modular home. The basement doesn't have traditional wooden floor joists that are easily accessible. The house sits on steel beams which are exposed in the basement. What is the best way to attach the wall frame to the foundation or the steel beams? Ideally I'd like to avoid drilling into the beams but can if necessary. Is there an alternate way to attach the wall frame to the foundation or are the beams the only way? I'm planning on putting in a drop ceiling. Thanks.

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    What is the height of the beams? I'm tempted to say you don't attach any of the framing to the existing home, simply to the walls and floor.
    – KMJ
    Commented Dec 12, 2023 at 16:13
  • KMJ, the bottom of the lowest beam is 7'4". Would you just put a ledger board to attach the wall frame to the concrete wall? Or would an L bracket suffice since it isn't load bearing. Isherwood - I edited my original post. I am planning on putting in a drop ceiling. Appreciate the help.
    – kel072931
    Commented Dec 12, 2023 at 16:23
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    Don't drill the beams without engineering approval. Putting holes in beams changes their strength and that could be bad. They do make clamps that screw on to an I-beam flange for attaching things. If you need to attach to the beams, that's probably the way to go.
    – FreeMan
    Commented Dec 12, 2023 at 16:38

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Because of the this-and-that structure you have to work with there's probably no simple, straight-forward solution. Here's how I'd tackle it.

  1. Determine your highest possible wall height. This will be the lowest point in the steel framing or something above that if you intend to have several ceiling heights.

  2. Frame your walls to that height and put them up. Use double top plates so you can properly lap them to tie intersections together1, and so you have more fastening for your suspended ceiling. The bottom plates should be fastened well to the concrete. Bracing depends on them being secure.

  3. Add bracing. This will be situation-dependent. Here are some ideas:

    • Place horizontal diagonals across the tops of the plates at wall intersections. You can use multiple of varying lengths where space allows, with attachments every 4 feet or so.
    • Run to the steel framing where you can attach in line with the member's orientation (or nearly so)--you don't want to tie in at right angles since that could stress those members in ways they weren't intended to handle. Nail to the wall plates and use clamps or approved fasteners at the other end.
    • Tie into the foundation. Expandable anchors and brackets or lumber would give you solid support for intersecting braces. You could avoid any attachment to the steel framing by installing continuous runs in a sensible grid across the top of your walls between opposing foundation walls.
    • Let one-by diagonal bracing into the studs2 where other options fail or use steel strapping in an X3.

All that said, drywall is heavy and you really don't need to go nuts here. Keeping the walls from moving laterally away from stabilizing intersections is the overall goal. Drywall offers a lot of diagonal stability itself, so doorways and very short walls are where most bracing is needed. Give your walls the bump-and-heave test and add bracing where movement is excessive.

The beauty of your plan is that you can easily add bracing later if you find a deficiency down the road.


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