Problem is that its zoned single family so if anything happens to it, you can't rebuild it.

This investment would make more sense for someone who wants to rebuild and do a complete tear down in my opinion.

After getting a settlement from his insurance company, he is looking to sell rather than rebuilding as he doesn't have the time or patience. - A couple is moving to Hawaii and they put the house, which needs a good amount of work, on the market.  

I had the structure raised and removed and don't plan on re-building.  

Easy to fix if the foundation for the pier is solid - put a temporary support next to it and rebuild the column, or go to a permanent steel (or 6x6 pressure treated wood, if you prefer) support.

I prefer replacement value because it covers the cost to rebuild.

Just have to run the numbers to see how it affects the basis. it will definitely improve the layout of the home and solve a problem I already was facing with a wall rebuild. 

The 4th unit will take longer as we need to demo the living room, bathroom and bedrooms completely and rebuild it all.

Obviously not a perfect solution, but it would save you lots of demo, rebuilding and probably some vacancy too.

Not sure what we are gonna do with it yet but if it's a tear down rezoning it to commercial and reselling it could be better than rebuilding a home.