What should the layers of brick walls look like?

We must replace walls in our brick home. When we tore the walls in the bedroom down, we found drywall, then wall studs, then felt paper, then wood slats. When you knock on the wood slats, it sounds hollow, like there is space behind that instead of brick. We haven't torn that yet-not sure what is behind it or if we should tear it out. Don't know where to put insulation. Trying to find out if that is typical. House was built in 1928. References to websites with diagrams would be very helpful! We don't want to tear out any support walls, but would like to put insulation in. We do need to take out any insulation that might be behind the wall due to water leakage.