Timber Frame Basement

Good Afternoon,
I'm new here so please forgive me as I learn to use the site (yes tips and help are greatly appreciated).
I inherited the family cabin in the mountains of Northwestern South Carolina. Currently, the cabin sits on black locust logs that have been holding up the house for going on 50 years and there is no sign of rot or insect damage at all. Time has settled the foundation to a point where the house needs to be jacked up and releveled. Since the cabin is going to be jacked up I have been thinking about digging out from underneath to build and close in a basement/ understory.
So here is my question, what does anyone think of my idea of building a (for lack of a better way of saying it) post and beam frame underneath from Black Locust? I know when dried it can be tough to work with or so I have been told.
1) The cabin sits on the side of a mountain of hard packed red clay.
2) I intend to install concrete footers that will exceed current local code.
3) My original thought was steel but the more I think about it naaa.
4) Back wall and partial side wall (subterranean) will be concrete block  w/ local stone veneer (eventually)
5) remaining 2 & 3/4  walls will either be Appalachian dovetail notched logs or conventional framed board and batten rough cut lumber of some species maybe locust or cypress?
I have been planning this out in my head for years and now is the time to do while I am still able to. I look forward to any helpful comments and questions. Thanks in Advance!
P.S. I have 2 acres of dense forest with Red and White Oak, Southern Yellow and White Pine, Poplar and probably a few other species to take down so if anybody is a sawyer with a portable mill or has recommendations in the 29664 zip code USA area let me know.

Hi Wallace, welcome to permies.

My thoughts on your basement project is to check the shrink/swell of the soil that your basement walls will be holding back. Soils shrink and swell based on how dry or saturated with water they are. The soils expand and contract each year. Some soils, when saturated, can become flowable- think mudslides. The USDA has a web soil survey site that contains tons of data on nearly all the soil in the united states. Among that, they have some data regarding suitability for excavating and building basements based on the kind of soil at your cabin site. While it won't offer engineering guidelines on what kind of basement walls are necessary to hold back the earth, I think it's a good start. Their website is:

https://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm

no timber in moist zones!!!

Thanks James for the link. I am planning to put in a french drain to combat saturation.

If the locust posts have stayed upright for 50 years on a hillside, I would say the soil is pretty stable for basement building.

It sounds like you are talking about raising the cabin enough that the new basement would be above grade on at least one side. As long as the underground portions are masonry of whatever sort, I think locust timber framing or log walls would be fine for the rest. Locust reaching below grade might be fine for your lifetime, but would eventually decay and cause the cabin to be destroyed. It's your choice whether to focus on your use or the very long-term existence of the building.

If the locust posts have stayed upright for 50 years on a hillside, I would say the soil is pretty stable for basement building.

Glenn, Thanks for your reply. Yes and kinda yes. The posts are indeed upright. The problem is, since my father died in 1988, nobody has kept up tweaking the level of the floor. My dad would occasionally go to a post, usually a corner and jack it up and either add a stone or a shim and lower it back down to level. I have attached a couple of pictures. One is the underside showing a post and the other is a stone. All that post is sitting on is one or in some cases two stones (thick) which make up the footer, if you will. Also the rim joist you can see behind the water tank the house actually sits about 6" ( to about) 24'+/- above grade on that side. To the left of the of the blue tank is the low side and there is already a cement block water diversion wall on the east corner to keep rain from rolling under the house and it does a great job. to the right and behind the camera point of view to the left (uphill) corner clearance is 3-4' and behind me to my right clearance is about 14-15'.
My plan:
1) Is to dig out the low corner (forward left) and build up the behind right to a finished ceiling height of 10'. If I pour a slab floor I will install radiant floor heat powered by a fireplace (so if anyone has plans already for how to do that I would love to know this too).
2) Since I am going to add a covered porch on the uphill side I will be even better able to divert water away from the foundation.
3) I have been researching ICF construction or just a poured wall for the uphill side which presents a challenge in itself. Since I am retrofitting to an existing building and just getting concrete to the job site much less a pumper to do a pour. I read something here from another thread that talked about doing a stacked stone foundation wall like the cabins and barns of 100 years ago. The issue of hydrodynamic forces against that wall is not really a large concern.
4)Since it might take me some time to get the wall completed And since I want to build a new master suite down there, what advice might you have on a species of wood to build the posts and beams out of if not black locust or is it not even very viable to do so?
I am more architecturally savvy that construction savvy I will take whatever free advice you're willing to share!

How steep is the hillside above the cabin? You really want the ground to slope away from the foundation for at least 5', 10' is better, on all sides. If you raise the cabin enough to do that on the uphill side, that will help with the amount you need to dig down.

If you want to support the cabin on timber before finishing the new foundation wall, I would place the posts a foot or so inside the foundation line (enough that you can build the foundation unimpeded by the posts). Then you can remove the posts when they are no longer needed. This would eliminate the need for special longevity in your framing.

A fireplace would not be able to effectively heat water for hydronic underfloor heating. A wood stove might be able to do the job needed, but I would recommend a rocket mass heater positioned relatively centrally (doesn't have to be in the middle of the floor). This would give the gentle radiant warmth you want with no dealing with water piping. It would also be possible to build a water tank into the thermal mass of the RMH which could heat the water for an active hydronic system. There are a few threads here with successful examples of doing that. Finally, since you will be building all new, you could route the heat exchange ducting of the RMH under the floor, making the whole floor the storage mass.

A thought about masonry - if you decide to go with concrete, a viable alternative to poured concrete is to dry-stack concrete block, with rebar every 2' or so vertically and horizontally, and fill the cores with concrete. I built my foundation that way (only with half as much rebar in the first section), and it has been perfectly sound for 30 years so far with no sign of deterioration. It actually withstood a pickup-sized dump truck full of gravel sliding down a slope and hitting it without visible damage - at the freestanding end of a 15' wing wall, the wall deflected 4" or so at the top, and sprang back to plumb when we winched the truck away.

Black locust has been used for fence posts for many years.  It is very rot resistant in contact with the ground. Probably the only better one I can think of would be American Chestnut, but it is, sadly, no longer an option.  I've seen Chestnut fence posts that have been in the ground since the early thirties that are still as good as the day they were put in the ground.  I've also seen Locust posts that are at least 60 years old that are still good.

If you are indeed serious about having lumber cut from your own timber then I would suggest following this link to the Woodmizer sawmill site and seeing if there is a local to you sawyer that will come out and mill for you.  https://woodmizer.com/us/Services/Find-a-Local-Sawyer  You would most likely be responsible for all the logging work, and staging the logs for sawing and providing some help to the sawyer, but the sawyer will cut your logs into lumber much more reasonably than what you can buy the same lumber for at the local lumber yard.  especially oak etc.

ETA:  That center post under the floor is helping to keep you floor from sagging.  The floor joists look, at least to me from that picture, to be spaced too far apart.  I would suggest an addition of floor joists and a beam under the center instead of that post.  It would be much more stable and may negate the need for that center support post depending on the span.

Glenn thanks for your insight. I have thought about just laying concrete block because I can work on it as I have time. mixing up mortar as I go. It will take me longer but I can do it myself.
As for in-floor radiant heat... 1) since I will be building a new master suite downstairs I really don't want cold floors in the winter and 2) luckily the number of really cold days and nights in low. And since I will be putting in a new septic system to increase the number of bathrooms I might go with a geothermal system. Just exploring options right now.

Walt Chase wrote:Black locust has been used for fence posts for many years.  It is very rot resistant in contact with the ground. Probably the only better one I can think of would be American Chestnut, but it is, sadly, no longer an option.  I've seen Chestnut fence posts that have been in the ground since the early thirties that are still as good as the day they were put in the ground.  I've also seen Locust posts that are at least 60 years old that are still good.

If you are indeed serious about having lumber cut from your own timber then I would suggest following this link to the Woodmizer sawmill site and seeing if there is a local to you sawyer that will come out and mill for you.  https://woodmizer.com/us/Services/Find-a-Local-Sawyer  You would most likely be responsible for all the logging work and staging the logs for sawing and providing some help to the sawyer, but the sawyer will cut your logs into lumber much more reasonably than what you can buy the same lumber for at the local lumber yard.  especially oak etc.

ETA:  That center post under the floor is helping to keep your floor from sagging.  The floor joists look, at least to me from that picture, to be spaced too far apart.  I would suggest an addition of floor joists and a beam under the center instead of that post.  It would be much more stable and may negate the need for that center support post depending on the span.

Walt thanks for your insight! Since I want to remove a lot of trees to expand the size of the house some, I figure I might as well get some lumber out of it. I will be taking an inventory of what I want to take out and will have a good idea tomorrow a rough guesstimate on board feet. I have a neighbor who is a forester and will fell them for me at a reasonable cost. The bucking and staging is a different story $$$. Might be better served to sell the timber. A friend has told me about a husband/wife team that has a portable mill and loves to barter so I'm looking into that too.
The beams to which you are referring a rough cut double thick 2x 10 yellow pine beams I think. I will measure them but they span 12 feet. There is lay the original question. I am thinking about "beefing them up" with a timber frame under it all. The house is 24' wide and without cutting them from my own timber, 24-foot beams would probably be prohibitive not to mention unmovable without a crane. Getting a crane up the mountain to the sight is all but impossible too. I should probably have an engineer work out the sizing but my guess is 8"x 8" post holding 8x10 beams should do the trick.

Unless you have a lot of timber it may be hard to sell.  I have a woodmizer sawmill of my own and do all my own logging as well.  It is a hobby, not a business etc.  I only cut for myself.  I use my tractor to drag logs from the woods to my mill site.  I've been cutting spruce that has been beetle killed lately and need to cut some more birch.  The spruce is being cut into dimensional lumber (2X6's etc) for a future shop and the birch I have been cutting into full size 1X4's that will be processed further for flooring in our next home or into live edge slabs for rustic furniture.  Please keep updating as you progress.  Many interesting threads get abandoned before the final product/project is revealed.  I will help with questions as best I can within my abilities.  How close to GA or NC is your cabin?  I used to live about 25 miles from Clayton GA before moving to AK.

Unless you have a lot of timber it may be hard to sell.  I have a woodmizer sawmill of my own and do all my own logging as well.  It is a hobby, not a business etc.  I only cut for myself.  I use my tractor to drag logs from the woods to my mill site.  I've been cutting spruce that has been beetle killed lately and need to cut some more birch.  The spruce is being cut into dimensional lumber (2X6's etc) for a future shop and the birch I have been cutting into full size 1X4's that will be processed further for flooring in our next home or into live edge slabs for rustic furniture.  Please keep updating as you progress.  Many interesting threads get abandoned before the final product/project is revealed.  I will help with questions as best I can within my abilities.

Walt Chase wrote: How close to GA or NC is your cabin?  I used to live about 25 miles from Clayton GA before moving to AKA

Walt Chase wrote:

Walt as the crow flies ... Clayton, Ga is 14 miles west and Highlands NC 11 miles north. I am on the SC side of the Chattooga River about mile and a half from Ga line and roughly 2 miles from the town (that is being generous) of Mountain Rest.

We would've almost been neighbors then.  Grew up in Helen, Ga.  Spent a lot of time in and around Clayton and surrounding areas.