Tying into a cinderblock foundation
Hello
I’m on a quest to design my own house addition, so much to learn… 🙂
One of the things I’m struggling with is how to tie the addition’s foundation into the existing foundation. I found some articles on Fine Homebuilding about drilling holes into the existing foundation and putting rebar into them. Possibly with epoxy.
That sounds good, but as far as I can tell – all those articles were referring to slab foundations. I have cinderblock.
I don’t know this for a fact (is there a way to find out for sure?) but I think the existing cinderblock in my foundation is hollow on the inside. Would it still be effective for me to drill holes in it for rebar? Would epoxy be of any use in this case?
Also, is there a trick for finding how thick the existing foundation is without drilling a hole in it?
Are there other means of tying in a foundation wall?
Thanks in advance.
Replies
The footing is under the block wall, and what sits between the regular surface hollow block and the less regular (but undisturbed or compacted) earth. Should be poured concrete.
This footing what you might want to drill into and epoxy some rebar into to help hold the new and old structure at the same elevation relative to each other.
If you are someplace you need to consider earthquakes or floods, the best plan is to have an engineer weigh in.
Oh, cool, thanks!
So I don't need to tie in most of the foundation, just the footing? It seems weird to me that there will end up a long vertical crack where the two foundation walls join. Doesn't that have the same problem as a block wall where the blocks do not overlap from layer to layer?
Thankfully there are no earthquake or flood worries here.
Depends on how high the wall is. And what kind of soils you have. (and how water behaves in the soil structure you have)
And if you will have one side open while the other side is buried. (Is this going to be a crawl space or a full basement?)
You can drill a small hole in the mortar and use a wire to check the inside depth, then patch the mortar. (or use foam or caulk to fill the hole)
You can also use a tape measure and some math to get an idea how thick the wall is. measure from a window to the inside and outside edge of a corner of the foundation. (or some other reference, like the edge of a specific block you can locate from inside or outside)
You can tie the wall together a couple ways. your local codes folks can inform you on the requirements, but you can always go over.
It is likely yours is hollow block.
The most solid will mean you have to break into the existing wall and fill one or two cores, and tie to the new wall with rebar and cement mix or grout. (you can put holes into every third course, more or less, use some bent rebar and fill a few courses at a time of the new and old wall together as the new wall goes up)
Less secure would be drilling holes in the mortar and using rebar or ladder mesh to tie to the new wall.
It will be as, if not more, important to seal the joint so that water does not enter (and then freeze, which would push things apart).
Also a good idea to make sure you have perimeter drains, waterproofing and fill that control the flow of water away from the wall, tied in with your existing basement.
Thanks Mike!