Main Support Beam Sagging? (Here's What You Can Do)

Are the floors in your home sagging? This is one of the most common complaints among owners of old homes. In most cases, all of the floors pitch toward the center-most stairwell in the home.

If you have sagging floors, cracks on interior walls, and doors that won’t close all the way, the issue tends to lie with the main support beams. The support beams are responsible for upholding the overall structure of the home and when they lose their own structural integrity, more issues can arise.

Once you notice a sagging main support beam, it should be corrected as quickly as possible in order to avoid the situation from becoming worse or more costly to repair. We’ll show you exactly how to identify the problem and what you can do to reverse it.

Most of the time, support beams and floors sag because the load-bearing posts that are holding them up are failing. It’s also possible that these posts are sinking or not the appropriate size.

Your first step in trying to identify the problem is examining the posts. You can use a screwdriver to investigate the base of your wood posts and expose any rot that may have contributed to the settling. If you don’t see any rot, the problem most likely has to do with its concrete footing. In this case, the footing is either sinking or has deteriorated completely.

Correcting sag by raising the main support beam that carries the interior walls and floors of a home is a very complicated task. This type of fix should not be attempted if you have little experience or are unfamiliar with structural engineering. If your main support beam is sagging significantly, the extensive floor leveling needed can be a major undertaking.

Even if you feel confident in your abilities, you should still consult the advice from an expert. The footings and posts support the entire weight of your home, so it’s essential that they are sized appropriately.

Hire the professional to evaluate every aspect of your project before you begin and obtain a building permit. Those who have experience with this type of job should be able to:

Before you begin lifting the sagging main support beam, any gas, plumbing, heating, or electrical lines near the beam, floors or walls must be released. If they are kept in place, the lines can rupture as the beam is being raised. Release the lines and support them with lumber that rests on the basement floor.

In order to stop the support beam from sagging, you need to replace the posts and/or footings. To do this, the beam will be raised using a hydraulic jack and a 4×4 piece of lumber. You will then shore the beam with adjustable steel posts.

Secure the hydraulic jack and shoring posts you need for the project. Both Hydraulic jacks and shoring posts can be purchased or rented from most dedicated home improvement centers.

To begin, position the hydraulic jack on your basement floor by laying it on top of two-level “weight-spreader” boards. These boards will be used to rest both the jack and the shoring posts to avoid any cracking of the floor.

Ensure that the boards are level and then place the hydraulic jack directly underneath the beam’s lifting location. Check that the jack is plumb using a plumb bob. Hydraulic jacks deliver a substantial amount of hydraulic force when lifting the post and beam. Select an appropriate wood that can withstand this force such as knot-free Southern yellow pine or Douglas fir.

Once you’ve laid down the spreader boards and the hydraulic jack is plumb and in position, prep the jacking post. Cut either a 4×4 or 6×6 post that will fit between the beam and the jack piston.

Determine the height between the top of the jack’s lowered piston and the support beam, then subtract ½ inch. Cut the jacking post to size and put it in position with a ¼ inch steel plate between the base and the piston. Close the hydraulic jack’s release valve and begin pumping the jack handle. This will raise the piston and place the jacking post snug up against the beam.

The final step before lifting is to position the steel shoring post. Place it on the spreader boards about 12 inches from the jacking post. Once the shoring post is in place and secured with duplex nails, you’re ready to start lifting.

Pump the hydraulic jack very slowly and carefully to raise the house beam no more than ½ to 1 inch. This will be just enough to release the weight of the beam on each post. Enlist the help of an assistant to simultaneously raise the shoring post to offer backup load support. Once the old post loosens, remove it and set it aside for reuse.

Jacking up a house can be a stressful experience, especially when you hear the walls and floors above the main support beam creak in response. Follow these rules for safe and effective lifting:

Once the concrete has cured for seven days, you can install the post onto the new plinth and footing. You can either purchase new posts of the appropriate size or reuse the old ones and simply saw off the rotted bottom.

Place the post in the same previous position and lay a sill sealer between the plinth and the base of your wood post. Then, reposition the hydraulic jack, lower the shoring post, and slowly open the valve of the hydraulic jack to allow the beam to rest on the new post.

The final task is to anchor the post to the plinth block and secure the post and the beam together. Use a galvanized connector strap, galvanized 10d box nails, and 1-1/4-inch concrete screws for the base of the post and block. To fasten the beam and post together, place a t-brace connector strap, level, and then secure with the same galvanized nails.