I am putting an 8 foot basement under my existing cabin. It is currently on 3" tall wooden posts. I have jackhammered out the rock and gravel (misserable job!) and now have my cabin temperarily on house jacks. My foundation wall at the back and around part of the sides will be 7' tall but most of the wall will only be 4' tall above the footing (my lots slopes big time down to the ocean). My question is can I build the foundation wall only 4 feet tall around the whole basement and then add the extra 3 feet on the back part of the foundation on a later concrete pour? I would leave rebar sticking up from the lower section to help anchour the top part to the lower part. If I build the back 7" tall in one pour it will be very tight between the wall and the rock/gravel behind the wall and I don't think I could get in there to waterproof the wall. If I build it only 4' tall, I can put in my perimeter drains and drain rock in as well as apply the tar and waterproofing membrane from inside the basement . After the second pour I could then reach over and waterproof the top 3 feet and overlap the membrane. My concern is that the joint in the wall may not be strong enough. Sorry for the long story...I hope you can following it!

 

You could finish the wall height a couple of different ways. If you choose to pour the additional wall you should perhaps leave a key-way in addition to the 1/2" re-rod extension from initial poured wall section.

If you choose to extend wall height in another fashion, you might consider continuing wall height with concrete block masonry. If you choose this method, consideration should have been given to spacing of re-rod extending from poured section to accommodate block cavity spacing. Block cores with rod could then be chucked with concrete at which time foundation bolt or anchors could be installed.

Good luck with this project.

bs5