Things You'll Need
No. 10 2 1/2-inch cabinet screws
Several 2-by-4 blocks
3/16-inch drill bit
Sagging cabinets are a sign that somethings has gone wrong. There are different reasons why cabinets sag. It is primarily due to improper installation, weak screws, or cabinet flaws. Whatever the reason, the fix is rather simple unless your cabinet is damaged. In most cases, removing the cabinets is not necessary, but you may have to partially detach the cabinets from each other.
Place a 2-by-4 on the counter to protect the counter top and cut blocks that will fit between the 2-by-4 on the counter and the cabinets. Slide wood shims in between the blocks and the cabinet to keep the blocks snug. If you have a granite top or another fragile type, place two 2-by-4s on the counter and only apply pressure where there is solid support underneath the top to keep the top from breaking. It is important to apply pressure only to the sides or back of the cabinets to prevent damage to the cabinets.
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Loosen the wall screws of the cabinet and then lift the cabinet and slide in the shims to raise the cabinet. It helps to have a helper to place the shims while you are lifting and to stabilize the cabinets. If the cabinets do not lift easily, place a shim on the bottom of the block so that the block is slightly angled and gently tap the block to lift the cabinet. Do this for the entire segment of cabinets that have sagged until they are tight with the ceiling.
Drill a 3/16-inch pilot hole in the existing holes or above or below the original holes if the original holes are too large already. Angle the holes slightly upward, which will help pull the cabinets upward and reduce the chances of the screws bending over time. Secure the cabinets to the wall with No. 10 2 1/2-inch cabinet screws. Cabinet screws have large, round, flat heads and a low profile.
If you have a soffit above your cabinets, drill 3/16-inch pilot holes angled toward the 2-by-2 frame of the soffit near the front of the cabinets and install 4-inch drywall screws.
No. 10 2 1/2-inch wood screws may also be used. A trim ring is added or the holes are counter-sunk so that the screws are flush with the back of the cabinets.
Be careful while loosening and removing screws so that the cabinets do not fall. Work on one section at a time and secure it firmly before moving on to the the next section. In extreme cases, you may have to work on one cabinet at a time instead of a line of cabinets.