Q. I live in a 40-year-old split-level home, and the main floor is showing signs of sagging (crack in ceiling, and kitchen counter flush to cabinet at one side is floating off cabinet by about 1/2 inch at the other end). This is the main floor and is about 25-by-25-feet over a 3-foot unfinished crawlspace. What is the proper way to shore up the floor, and is it something a DIYer can tackle?
A. Sagging floors in older homes are not uncommon. A lot of times, I will see extra supports that have been installed by a homeowner or contractor.
There are two different scenarios that can cause sagging. One would be that the main support beam is sagging. That would cause the ceiling to crack. The other scenario is sagging floor joists, which you would notice by a dip in the floors.
I would assume the beam is sagging because the kitchen wall has settled, causing the ceiling to crack. If you have a laser level, it is easy to check the beam for sags. If not, you can stretch a nylon string from one end of the beam to the other to check for low points along the length of the beam. Pull the string as tightly as possible and place a 3/4-inch block of wood at each end of the string so that the string is not touching the bottom of the beam. Then use another block of 3/4-inch wood to check at various locations along the beam.
There should be piers supporting the beam every 4 to 6 feet. Check to see whether the piers have settled or whether the beam was installed using wood shims between the beam and the pier. Wood shims will fail over time, allowing the beam to sag. Replace wood shims with large metal washers you can find at home and hardware stores.
If the piers have settled, you will need to dig a 2-by-2-foot, 12-inch-deep hole close to the settled pier. Fill the hole with concrete. When the concrete has dried, install a jack post to add support to the beam. Do not try to lift the beam all at once. Once the jack is snug against the beam, give the screw a quarter turn every four to six weeks. If the walls above the jack start to crack, quit adjusting the jacks.
For sagging floor joists, install two concrete footings (the same as required for the pier). Add two or more jack posts under a 4-by-4-inch treated wood beam installed perpendicular to the joists half way between the exterior foundation wall and the main beam. Adjust the same as you would for a sagging beam.
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