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The one thing people skip that bites them later is verifying which walls are actually load-bearing before you touch anything. You can't just guess based on how a wall looks or where it sits. Run a straight line up through the structure - does it sit directly over a bearing point below (another wall, a beam, a post)? If the wall above doesn't align with support underneath, it's probably not load-bearing, and forcing headers in unnecessarily wastes money and creates problems during renovation. Get a structural engineer to confirm if you're unsure; it costs less than fixing a mistake.
Once you know you're dealing with a true load-bearing wall, the previous answers nailed the key pieces - doubled top plates, properly sized headers, solid rim board - but the detail that changes everything is how you connect that header to the king studs and trimmer studs. A lot of DIY installs nail things together and hope, but you need enough fasteners in the right spots to transfer the load safely. The connection between header and supporting studs is where walls fail, not usually the header itself if it's sized right.
The foundation check matters too, but even before you go down there, make sure the wall itself is plumb and the plates aren't sitting on rotten sill stock. If the base is compromised, no amount of proper framing at the top fixes it. Build from the ground up, confirm your support path at every level, and don't assume anything about old construction.
Load-bearing walls need doubled-up top plates and headers over openings sized for the span and load they're carrying - are you dealing with a specific opening size or wondering about the foundation side too? The studs themselves should be 2x4 or 2x6 depending on height and load, spaced 16 inches on center, and you'll want to make sure the wall sits directly on a properly supported beam or foundation below it. The tricky part is getting those headers right, since an undersized one can cause sagging down the line, so if this is for an actual build you might want to run the specs by someone who can see the whole structure.
maker1977 asker
Mostly dealing with header sizing for a 12-foot span on the first floor - the foundation's already solid. Got any quick rules of thumb for calculating header depth?
The foundation detail matters way more than people think - I ran into trouble once reinforcing an old wall upstairs without checking what was actually holding it up on the first floor, and it turned out the load wasn't even going straight down like I assumed. Get a structural engineer involved if you're not 100% sure about what's underneath, because guessing on doubled plates and header sizing when the load path is unclear is how you end up with settlement or worse. The doubled top plates and proper headers are definitely part of it, but they only work if you're actually transferring the weight to something solid below.
Make sure your header size matches the actual load path above it - don't just eyeball it or copy what worked on a different house. I once helped a friend demo a wall in his kitchen and we found a single 2x6 header spanning maybe 8 feet with what looked like a second-floor bedroom sitting right on top of it. Turns out the original framer had undersized it, and the drywall was cracked all over the place because of settlement. We had to sister in reinforcement and it was way messier than getting it right the first time would've been.
The key things most people nail down are the doubled top plates and the trimmer studs on both sides of the header, but the part that bites you later is the bearing point. Your header needs to sit fully on the trimmer studs, and those trimmers need to transfer the load straight down to the foundation or whatever's holding things up below. If there's a wall or beam underneath, great - but if you're directly above a rim joist or a span with nothing supporting it, you're asking for trouble. Run your vertical load straight down through the framing and don't assume the floor system can just hang it.
What's the opening size you're dealing with, and do you know what's under it? That'll tell you whether you need to go bigger or if standard framing lumber will handle it.
Opening's about 6 feet, kitchen to dining room. Full second floor above it with bedrooms. Nothing underneath but rim joist and floor joists.
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