Speaking from experience of the last few days, you will likely have lots of dirt and mud when you tear them down.
That's good to know. I wish I had known earlier about the bridge rules.The thing you read may have been about bridges. Sometimes when you demolish a bridge, you cannot build another one in the same space because for some reason houses and PWPs can be put near an existing bridge, but to build a new bridge, you need a lot of space around the bridge to be open. You don't have to worry about it for any other PWP though, just bridges.