While many think that saving an existing structure is more cost effective when doing a build like this there are a few things to bring up. As mentioned previously, we discovered the lack of rebar in much of the foundation. As wall were cut open we became more concerned with transfer of weight of the new structure on the old foundation. Due to these concerns the architect went outside of the existing curved walls with the new footprint. This would allow us to transfer the weight to a new footing that we constructed and allowed us the confidence of proper weight transfer to the perimeter area.
We were able to conserve the existing round walls of the original design in the basement but also raised new problems along the way.
While the old support walls were low and did not allow for the headroom of the final vision this will easily be compensated in the framing arena. New pony walls will be erected on top of the old walls that will raise the ceiling of the basement area. Imagine the effort of building 2’ support walls that are load bearing and not one of them being straight in 200 linear feet, time consuming but not the end of the world by any means.
A more difficult problem was encountered however when shaping the new full height ICF curved walls and realizing the difficulty involved with the forms. ICF walls are amazing things to build and erect, they can be fast and simple to install in new construction and anyone who has seen followed one is simply amazed at the speed of stacking them verses standard form framed concrete walls. To add the benefit, amazing insulation factor can be gained and all with the strength of standard concrete and rebar, what is not to love?

Did I mention the fact that ICF blocks are modular designs? That being said, most block manufacturers make blocks in standard size increments. These systems are made to be easily installed on level foundations and footers where modern attachment have been engineered into the first pour. Proper rebar schedules are required to work with the blocks so that the webbings are aligned properly in the foundation. While one can be modified here or there, imagine the extra time required to modify a wall when it is off layout. How about curved? You can order your ICF foundations with pre curved radiuses but they only come in a few flavors and sizes, after that you are required to cut each and every block, protect the internal webbing which will later become the attachment point for the bearing ledger and then re-glue them back with expanding foam and make them strong enough to not cause deflection or blow outs during the pour or while vibrating the walls. Opt to but hem pre done, you can expect to shell out twice what the original cost would be.

Our specialty subcontractor for this job has had more experience with these systems than anyone I have ever met. He has traveled all over the US and worked for numerous ICF manufacturers as a trainer for their systems. In his words, “this was the most difficult job I have done to date.”
One entire wall had to have each and every starter block taper cut to conform to the existing wall and then still align perfectly 8 vertical feel later over a grade beam where each block has a ½” by ½” alternating tooth pattern that holds the forms together. Layout becomes critical for these and where the walls were not the perfect length for the ICF, they were required to be cut, modified and then reinforced to support the pour.
Once again if this were a fresh build, these things could be easily overcome. Our blocks need another 2” in wall length to properly lock together. Fine just extend the foundation 2” and no problems arise.

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Greg Christianson

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