Hello, I'm new to the forum and I have a question about post bases. I am building a timber frame barn that I am converting into our home and my posts will sit on my finished slab.
I would like to use hidden post connections so the posts will be flush on the concrete and do not have to be trimmed out.
I was thinking about drilling and epoxying all thread or rebar for the interior post connections and using a knife plate post base for the the posts on the exterior wall or some other concealed base if I can find them.
I haven't found any manufactured knife plate bases and was wondering if anyone had any ideas for a concealed post/column base?

Hi Ron. There are lots of ways to do this, but the two problems you are trying to solve are:

a) secure conection - you don't want the post to move side to side, of course, but also, you don't want it to lift up in high-wind conditions. The simplest solution is probably a simpson tie down strap such as model STHD14RJ. The hook end is embedded in the concrete. Make sure the hook is looped around the rebar. The top of the strap is nailed to the outside of the timber where it will be hidden by the perimeter wall. You'll probably be fine just pinning the non-perimeter posts, to solve the side-to-side issue, and ignore the uplift issue for those posts.

b) moisture barrier - avoid placing the end grain of the timber in direct contact with fresh concrete. The timber will wick up moisture and stain the timber (or worse). I usually use a barrier of pressure treated lumber which will be covered by baseboard trim. In your case, where you don't want any trim, I would try to embed a pressure treated lumber pad in the slab, flush with the top of the slab. Be aware that any subsequant spill on the floor has the pontential to run under the post bottom and wick up. Some type of additional moisture barrier might be in order, such as a square of roofing felt, which will get crushed into the post bottom.

I'm eager to see other proposals. I'm always learning new tricks on this forum. CB.

CB, Thanks for the help. That's good advise. I've heard of cutting a piece of roofing moisture membrane and placing under the post but I like the idea of the felt because it would get pushed into the fiber of the wood.

Derek, Thanks for the reply,yep that's what we did also with a lot of compacted screened rock. I think I'll make up some steel base plates also for the perimeter posts. I appreciate the input on the timbers wicking up moisture. Good luck with the pour.
RL

Do you guys have any pictures of what you are talking about. I'd like to understand but am having a little hard time picturing by the description. I am particularly interested because I plan on building my own timberframe withing the next couple years and am planning it now. I am not planning to have a basement so I am trying to figure out what type of foundation I need for my frame. Initially I was thinking on a slab, but then how do you route plumbing and electrical and heat/AC? I'm now thinking that a crawlspace is needed. Any opinions or pics? I think this relates to the mounting of the posts in that it raises the question of how the pluming, electrical and AC/Heat will be handled. thank you, Brad

I'm not sure if this is exactly what has been described above, but I have these pictures of something I've seen done at a guild raising.

Here is a shot of a base plate that has a center piece going up into the post:


Then the base is bolted through these side holes and then plugged over with pegs, I believe:



Then when the frame is raised the post sits on another steel plate in the concrete that has a j-bar or something similar to that in the concrete:



Then the two plates are welded to each other.

I was going to take a series of pictures of the jig/rig the timber framer used to cut the slot in the bottom of the post using a chain saw but my camera malfunctioned and they all came out very blurry....

Hope that helps...

Jim Rogers

Good pics, thank you. But I still don't understand how plumbing, electrical and HVAC are run with a slab system like that, especially the plumbing. Do they then build a flooring deck on top of the slab?

Jim, nice photos of the knife plate. That's a great way to conceal the base plates for that flush to floor post look.Thanks

Brad, I am doing a radiant heated slab as our finished floor that has a troweled 4'x4' stress joint grid which we will acid wash, grout the joints and seal for our finished floor.
I basically did a slab on grade in which I formed and poured 10"x24" footers around the footprint of the building. Then I formed an 18" tall stem wall on top of that using 2" foam Eco Block with rebar inside. For a one guy show that was easy.
I ran and stubbed my utilities and septic line under the footer and then up into the building. I filled and compacted gravel leaving 5" from the top of the foam for a slab/finished floor. All of the ground plumbing is then laid on the gravel at the appropriate slope for drainage with stub outs for the drains and vents that have to go upstairs in the exterior walls. We will use rigid foam in between the timber posts on the exterior walls for insulation so the drains will be in those walls. They don't hold water and they will be surrounded by foam so that is fine. The inside walls and our second story floor joists will be the chases for our water and electrical.
I also formed in the gravel 10 footers with rebar baskets for my interior posts. We poured the 10 footers first then the 18" stem wall and then the 5" slab all on the same day.
Hope that helps.
Ron

I have a question on anchoring my post to my basement.


I already have my floor joist and sub-flooring in place, I was going to have steel plate sitting of the floor with a steel rod (prob. 1"diaX18"length) going through my flooring down anchored to the foundation, and a steel plate attached to my post. Once in place, just weld the two plates together. Do you have any other suggestions or concerns?
I already have my anchor plates for the bottom of timbers.
I'm trying to make this as easy process as possible while the timbers are being set.

Thanks