drywallstuds
My stud finder seems to have trouble when I'm in the corner of two sheets of plaster/drywall. Can I just assume there will be studs behind each wall in the corner?
And what about where the wall meets the roof, is it safe to assume there will be a top plate behind the highest part of the wall plaster/drywall?
Yes, in most US residential construction they are 16" center to center. Most of your standard tape measures have every 16th inch noted in red or some other way. Some internal walls may also be spaced 24" on center.
However, there may be exceptions where a door window or odd length wall is used so be sure to verify with a stud finder or a knock on the wall to check.
As Legion600 suggested, you probably have steel studs as furring strips. You need to be sure you are not hitting protection plates installed on wood studs.
These protect electrical or plumbing lines close to the stud face, and you must never attempt to drill through these. Usually, if you drill several inches above or below such plates, you will hit wood. If you are hitting metal along the entire stud length, it is not a protection plate, but a metal stud. Metal studs in this application should be fairly light gauge and easy to drill through. Protection plates are about 16 GA and are not easy to drill through.
You may anchor objects to metal studs. They are sturdy enough when finish sheathing is attached along their length. Do not use toggles, the hole required is too large. It's best to use a number of self-drilling screws that are barely long enough to engage the stud face material after passing through the mount and wall finish. This avoids damaging any lines routed through the center holes of the stud. You can also use self tapping screws into pre-drilled holes, but drill very carefully so as not to damage any underlying lines when the drill breaks through the face material, and again, use appropriate length screws.
Best Answer
Those are all reasonable assumptions. But, you never know for certain whether anything was built by someone who knew what they were doing. Or whether it was inspected.
I'd guess those assumptions are accurate 90% of the time?
Safe? Well, that depends on what you are doing in those areas. I wouldn't hang anything heavy that could fall and hurt someone if the assumption were not true (without 1st verifying the assumption).