Logic behind Updating apps and Free Space

[MarqueeK]

I've got a 16GB 3rd gen iPad that's pretty much full up to the brim.
When I try to update some sizable apps it tells me that there's not enough space left.
Is this because the new version is installed before removing the old version, meaning that there's needs to be enough space for two of the same app to exist momentarily?
This seems evident from the fact that when I delete another app (that is of comparable size to the one I'm trying to update) to free up some space to let the update happen, and then try to reinstall the app I deleted to make space, it installs fine.
This is more of a curiosity for me more than anything else.

Of course, I wouldn't have to deal with this crap if I buy a bigger iPad but it was gift from my wife, so can't complain.

 

[Daveoc64]

Is this because the new version is installed before removing the old version, meaning that there's needs to be enough space for two of the same app to exist momentarily?

Yes.

iOS Apps are effectively a collection of folders.

Each App has its own set of folders, where it (and you) can store data as well as the App itself.

When an App is updated, your device (or iTunes) downloads a fresh copy of the App and then your data (i.e. the App's "Documents" folder) is moved over to the new copy of the App.

To do that, your device needs to have enough space for the App to be installed "again".