I'm trying to find studs on an exterior wall of a recently (10 years?) renovated house that I'm renting. I've had issues before where the studs in a wall seem to be a bit wonky - irregularly space, sometimes studs that don't go all the way up to the ceiling, etc. I also have problems where my stud finder will think there's a stud, but when I screw in there, it turns out there is no stud.
Fast forward to today - I'm trying to hang some curtain rod holders over a double-door to the outside on an external door. I found one stud to the left of the glass door, but I'm struggling on the right. My magnet stud finder found one down low, but it doesn't seem to go all the way up. And my other-kind-of stud finder, gives me unreliable lights when I run it across the top of the wall looking for one. It has hinted at a couple of places that turned out to be empty behind the drywall.
And, oddly enough, there don't seem to be any above the door frame - though when knocking on it, that part of the wall sounds solid (as opposed to the hollow sound you get on most walls).
So my question is this - when contractors are doing renovation work, and may be adding extensions or things like that, are there any rules of thumb for how they build things out? Are there times when the studs above a door frame would be differently spaced than those below? And are there any other kinds of wall construction that would lead to me finding so many frustratingly non-standard walls in a recently renovated house?
For what it's worth, here are 3 pics of the inside wall (since a single photo is all washed out due to the light from the door), and one of the outside.