When measured from the kitchen archway, which is in a non load-bearing wall, the wall thickness measures from 4-1/4" to 4-1/2".

The walls around the front and rear stairways, which are interior load-bearing walls, measure from 5-1/8" to 5-1/4".

Could my walls be plaster over double 3/8" rocklath?

The core of the drywall looks a lot like the fire blocking compound around the bricks which seal the wall cavities. Did fire codes specify double-thickness drywall back then? If so, it would probably mean that my ceilings are also double-thickness too, right?

As a side question, I'm trying to figure out if my house is platform framed or balloon framed. I cant see any interior partition walls from the basement. They are built on top of the sub-floor. That would mean the house is platform framed...

However, I can see the bottom of the wall cavities for the exterior walls and interior load-bearing walls (which all rest on from the basement, which would be balloon framing, right? I also noticed that I have fire blocking in each exterior wall cavity at each floor level.

Isn't 1948 kinda late for a balloon framed home? I thought builders had all moved to platform framing in the late 30's...

Some picture to help explain:

Two layers of drywall under staircase ceiling in basement.

Fire-blocking at base of interior load-bearing walls.

Fire-blocking at base of exterior walls.

Fire-blocking at exterior wall seen from third floor joist space.

The two parallel interior load-bearing walls are for the front and rear stairways. These two load bearing walls, which travel from the very front to the very back of the house, are carried by four solid beams and columns. All the floor joists are notched over the beam at one end, and the sill at the other. The beams have 2x4 ledgers nailed to their sides to support the bottom of the joists.

It disappeared as much as from fire risks in the large unblocked stud cavities (and someone may have blocked yours to mitigate the risk) as from a lack of long suitable framing lumber.

Platform framing allows the use of shorter studs, and bottom plates, top plates, and the platform all serve to block the stud cavities.

I'd lean more toward balloon framing, as I have all those exposed exterior wall cavities where the exterior studs sit on the sill plate. They are fire blocked at each floor level, so there's not much worry about a fire.

That means that my interior load bearing walls are balloon framed (the balloon studs rest on a solid wood girder, and the wall cavities are fireblocked.), but the non-loadbearing partition walls are platform framed (built off of the subfloor).