obviously not all, I shouldn't have said that. Naturally where you have windows and such it will be blocked. But if you go up into the attic or down to the basement and shine a light often you can see all the way up and down. a lot of times if there has been a substantial rehab of the building you will see blocking has been installed but a lot of times work on these old buildings a permit is never pulled and they don't do the work up to code.