Has anyone ever tried mounting stair stringers to a raw log support?

Working with round logs for structural framing is a nightmare if you aren't ready to spend hours with a chainsaw disc on a grinder and a good compass for scribing. The reality of those rustic log beam setups is that they often look great from ten feet away but are structural disasters up close beacuse the wood is constantly moving. If that log wasn't kiln-dried—and let’s be honest, almost none of them are—it is going to shrink and check as it seasons. That means every single connection point you carefully scribed is going to have a massive gap within two years.

When you're trying to attach stringers to a round surface, you basicly have to flat-spot the log wherever a structural member hits it. I usally snap a chalk line along the top center of the log and another one along the side to keep my orientation. Then you use a drawknife or a power planer to create a flat landing zone for the stringer to seat against. If you just bolt a flat stringer against a curved surface, you are creating a perfect little pocket for water to sit. That is how you end up with a rot-fest in under a decade. You are much better off using **galvanized spacers** or stand-offs to keep some airflow between the log and the stringer. The layout is the hardest part because you cannot trust the surface of the log for your rise and run measurements. I have seen guys try to measure off the bark and it is a total mess every time. You have to set up a string line or a laser level that represents your theoretical perfect beam and pull all your measurements from that datum. It is essentially timber framing logic rather than standard stick framing. You're building a square staircase inside a round hole.

If you see gaps or bolted-together scraps tucked up against a log like that, it is usually a sign someone prioritized the look over the engineering. Those massive logs hold a ton of moisture. If you trap that against a stringer with no room to breathe, the fasteners will eventually just pull right thru the softened wood. It looks cool, but it is a hell of alot of maintenance to keep it from becoming a total death trap.

The idea of a "theoretical perfect beam" inside a messy log is wild. I’m picturing myself trying to hold a string line and a tape measure while the log is rolling around. When you mentioned those galvanized spacers, are those just standard washers stacked up, or is there a specific bracket that works for a curved surface? I'm also wondering if you have to treat the wood where you've cut the flat spots, or if the airflow alone is enugh to stop the rot. It sounds like alot of precision for somethig that's supposed to look "natural."

If that log is truly unpeeled, you’re asking for trouble. Once that cambium layer dries and the bark starts sloughing off, every single one of your tight connections is going to be loose. I’ve seen guys try to bolt thru bark and it’s a disaster within two seasons. For spacers, I ussually skip stacking washers and go with thick HDPE blocks or even galvanized pipe nipples over a heavy-duty through-bolt. It gives you a solid stand-off so the stringer isn't soaking up moisture from the log's sapwood. Also, make sure your footers are way overkill. A green log that size weighs a ton and will settle unevenly if you're just sitting on a standard deck pad.

If you're keeping the bark on, you better be ready for a bug hotel. I worked on a porch once where the homeowner insisted on the "natural" bark look, and two years later we were pulling handfuls of frass out from behind the stringers. For the connections, I usally go with long GRK structural screws instead of thru-bolts. They let you pull the stringer tight against your flat-spot without needing a second person to hold a wrench on the back of a massive log. Just watch out for the tannins in fresh logs—they'll chew through cheap zinc fasteners fast if you aren't using somthing with a high-grade coating.