How to attach a top plate to a plaster and lath ceiling for a closet?

Question

I'm looking to add a closet to a room in my house. I took down the walls (and have since had drywall put back up) so I know where the studs are in the walls, but I don't know where the ceiling joists are. I don't have access to them from above since there are hardwood floors upstairs.

I'm not sure how I should go about attaching the top plates for the closet. Can I just screw them into the lath? Will this crush the plaster and cause everything to come crashing down? Should I (and how would I?) remove the plaster above the closet so I can see the joists? What if the closet walls line up with the wall studs, but the ceiling joists don't?

Answer 1

It should be fairly easy to determine the direction the joists run. In older homes they almost always run across the short dimension of the home's footprint. Once you know that, and you have your walls laid out, just start drilling holes with a small bit through the plaster and lath until you find a joist. They should be on 16 inch centers from there. Simply run 3 inch construction screws through your plate, through the lath, and into the joist. You will not crush the plaster, but watch for signs of cracking as you tighten things up.

If you find that you have a wall running parallel to the joists and between them, you'll probably want to just glue the top plate in place. There shouldn't be very much sideways force on it anyway. I would use heavy duty construction adhesive and run a few screws into the lath to hold it in place while the adhesive sets. Plaster and lath is actually very strong and it's unlikely you'll do any damage this way if your wall framing fits snugly. Connect the ends of such walls securely into other walls or joists as you can and don't worry about it from there.

The right technique would have been to install blocking between joists while you had the plaster and lath out. Obviously it's too late for that now but it's not a big deal.

Answer 2

Stud finders work well through plaster. They are accurate, inexpensive and ubiquitous. Since your closet wall is not load bearing but a simple partition wall, attaching the top plate over plaster is best done with construction adhesive and screws. Pre-drill pilot holes with a masonry bit through the plaster to limit cracking. Renovation projects using kiln dried lumber is typically screwed. Nails are generally used for new framing when green lumber is used.

Answer 3

Using a sandwich of sheetrock (or drywall) between the top plate of the wall and a ceiling joist is a risky proposition. For example, should the sheetrock become wet from a roof leak or some other means of degradation, there is no true mechanical connection between the primary load points. A better option is using a Sawzall to cut slots 3-1/2" wide ( the width of a 2x4) x 4-6" long in the sheetrock at every other ceiling joist. Then tack-nail strips of 3/4" plywood or pine board into the slot openings. Install the top plate and drive fasteners through the strips into the ceiling joists with 3-/12" screws or nails. With this method, the sheetrock is disconnected from the wall. Also, it prevents the sheetrock from cracking since it remains intact on each side of slots. This particularly helpful if there is concern the sheetrock has dropped over the years. By the way, should the wall be running parallel to the ceiling joists, cut the same slots in the sheetrock every 32-48". Go into the attic and nail 2x6 blocking across the joists at each slot. Continue the process as mentioned above. It sounds like a lot of work. But the first construction of a wall will convince you of the method's simplicity and strength for a lasting result.