Foundation - Timber sill on CMU?

[Dave in MD]

I'm pondering the most cost effective foundation for our structure (a TF shed/greenhouse with overall dimensions 20' x 19'; see separate thread: https://forestryforum.com/board/index.php?topic=111973.0).

I had originally planned on poured concrete footers (16" x 8") at frost depth with an 8" thick poured wall coming up to the sill level. However, the first quote I received for the foundation work was way higher than anticipated.

I'm considering using CMUs (cinderblocks) to build the walls. I am fortunate to have access to a large volume of CMUs for free, and I could lay the block myself. The blocks would be filled with concrete and rebar, with anchor bolts every 4' OC. However, I'm somewhat concerned about the point loads from the posts. Would a timber sill (8 x 8 white oak) be sufficient to distribute the weight? Am I overthinking this?

Thanks!

[Don P]

Yes it will work. I'm currently building a full basement CMU wall under a 2 story house. We are replacing the existing termite eaten 8x8 sills with treated 8x8's. Do make sure to pour the cores solid under any post loads, the rest is really a curtain wall between those points. It doesn't look like you have a significant difference in level inside to out, what is called "unbalanced fill". With our basement there is up to 7'  of unbalanced fill so i consulted the tables in the code which specified block thickness, 12", and reinforcement, pour cores every 4' with 1/2" rebar. With that in hand we chose to anchor at the rebar locations. It is a good idea and often specified to use bond beam block at the top of the wall and run rebar in the block around the top of the wall but in any case at least pour a minimum 4" thick cap in the top of all cores and mud it in well, termites love it when they have a hidden path up.

[Dave in MD]

Thanks Don!