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Two story, midwestern suburban colonial built in 1947. Gable roof. Plaster walls and ceilings. House faces north, and ceiling joists run north-south direction. I am hearing rodents inside of interior bedroom walls and then running across my ceiling in a diagonal direction, i.e., northwest to southeast. I didn't think there would be any space between the ceiling and the joists that would allow free range movement like that. Am I misunderstanding how it's constructed, or is this a sign of a problem (other than rodents)?

  • There is a type of construction called “Balloon” framing I thought this style went out of style by the 20’s maybe slightly later the bottom plate is below the floor level and the top plate is above the ceiling level , if you have this kind of construction critters can use the walls as a passageways to the attic as fire blocking was not required back then. I am leaving as a comment as I have only worked on a couple of this style construction. Rare on the west coast, I thought the Chicago fire was part of the reason for its downfall but high quality vertical grain lumber may have been part also. – Ed Beal Apr 25 at 22:24
  • Thank you Ed...I believe I have that type of construction. I see top plates of my walls when I look between the joists and dig through the insulation. Might explain why I don't see any wiring leading to ceiling lights? Seems like my bedrooms are a series of boxes built within the box of the entire upper floor. – Mike Apr 27 at 12:21
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No there is no space between your plaster/wall and the joist. However, old house walls were sometimes constructed without a top plate or bottom plate so it would be no problem for a rodent in your wall to get to the attic and run around.

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  • Is there no insulation in the ceiling? If that's the case, you would not likely be able to distinguish that the rodent is moving diagonally OVER the joists. Even if there is insulation, they may have, over time, dug tunnels in it to move rapidly in that direction. – JRaef Apr 25 at 16:55
  • Ok, but how do I hear them run across the ceiling in a direction crossing the joists? I went up there since I first posted - the space between the joists is filled with that insulation that looks like shredded newspaper. They couldn't run along the joists either, so there must be space above the ceiling for them to run. Also, how is electrical wiring run to my ceiling lights? No wiring visible in my attic, so is the wiring running in the space that I think the mice/rats/squirrels are in? Sorry for being so dumb. – Mike Apr 25 at 19:06
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    Okay this is very unlikely the case but I suppose it's possible that if this house was remodeled and the ceiling was really unlevel at the time the contractor might have run 3/4" thick by 2" wide lumber in the opposite direction of your joists shimming where necessary to make the ceiling level then drywalling thus creating a gap. However you say it's lath and plaster ceiling so this wouldn't be the case. Your electrical wiring likely runs through small holes drilled through the joist, not big enough for rodents, or at least certainly should not be. – PennyPincherWannaBeHandyMan Apr 26 at 5:18
  • Agreed that it's possible that furring strips were added to the bottom of the joists to level them out (leaving small rodent sized gaps) then new plaster & lath applied, but unlikely. By the time this kind of repair work would have been done to level the ceiling, drywall/plasterboard would have been a much more likely option instead of plaster & lath. It's possible that what you're seeing is plaster over a plasterboard-type substrate and that the critters are making their way between the joists and the plasterboard. – FreeMan May 27 at 13:41

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