The two most common drywall thicknesses for ceilings are 1/2-inch and 5/8-inch. For most standard residential applications, 1/2-inch drywall is sufficient and widely used. It provides adequate support and is lighter and easier to handle during installation compared to thicker sheets. However, 5/8-inch drywall is often used for specific cases where additional benefits are needed. It is heavier but provides superior sound dampening and fire resistance. You should consider using 5/8-inch drywall for ceilings in commercial buildings, between a garage and a living space, or above a finished basement to meet building codes or for enhanced soundproofing.

Yes, you can install drywall over plaster, but there are important factors to consider. While it can create a smooth, flat surface, it is often not the best approach. Installing drywall over plaster will increase the wall's thickness, which can cause issues with existing window and door frames that may no longer fit. You might also need to adjust power outlets to keep them accessible. A better, though more expensive, option is to remove the old plaster and lath entirely before installing new drywall. Drywalling directly over plaster seals in the old material, and if any problems arise later, you will need to remove both layers down to the structural beams for repairs. Given the potential complications, this job is best handled by professionals.

There are several things you should not do when installing drywall. Common mistakes include: adding too many screws, over-sanding, not adding backing support, and installing drywall unevenly. You also should avoid screwing into the same place twice, installing Sheetrock with tapered edges on the outside, and making too many joints.

A common cause of separation between a wall and the ceiling is truss lift—this can happen to the ceiling of rooms directly under the attic when the seasons change and wood building materials dry out, shrink, and shift. Roof trusses often dry out at different speeds, and if the bottom pieces dry out faster than the top pieces, they can shrink and pull the attached drywall away from ceilings and walls, causing cracks. Fortunately, truss lift is only a cosmetic problem, not a structural problem, and you can fix it by separating the ceiling drywall from the roof trusses, and patching the cracks.