Normally, the foundation pour for a small home like the one we’re working on at 1566 Sanchez could be done in a week.
Unfortunately, homes in San Francisco (and many other dense urban environs) are typically built as what are known as Zero Lot Line homes. That means that the homes are built right up to the property line on each side, leaving anywhere from no space at all (for attached townhomes, for example) to an inch or two between the homes.
With a zero lot line home, your foundation is immediately adjacent to that of your neighbor’s. When excavating down to add square footage and to build a new foundation, you’re most likely exposing your neighbor’s foundation where before it had been supported by your foundation or soil. To protect the structural integrity of the neighbor’s home, you can use various proven techniques from rock to temporary wood walls to shore up their foundation and provide support so that it remains stable while you set up the wooden forms and the reinforcing steel bars (rebar) to prepare to pour your own foundation.
Unfortunately, this means that you can also only remove small sections of the shoring at a time to provide them with maximum protection while you pour the foundation in sections.
For 1566 Sanchez, we’ve done at least a half dozen pours of sections rarely more than 8 feet long at a time. Unfortunately, you have to wait for the concrete to cure between pours, so the pours are a minimum of a week apart, but thanks to a super-duper-ultra-rainy winter, rain delays dragged that out further.
Nevertheless, we’re just about there! We’re completely done with all of the walls adjacent to the neighbors on both sides and there’s just one foundation section to go and we are done with all of the structural foundation walls!