How To Repair a Load-Bearing Post (page 2 of 3)

Change Text Size

Change Text Size
|
Bookmark

Bookmark

Del.icio.us
Digg
Reddit
Facebook
StumbleUpon
TwitThis
|
Print
|
E-Mail

How To Repair a Load-Bearing Post: Identify the Problem

Floors sag because the posts supporting a house beam are failing and/or the footings holding those posts are undersized and sinking. Diagnose the problem by seeking the easiest solution first; go further only as needed. If your posts directly contact the floor, start by using a screwdriver to probe the base of your wood posts to reveal any rot that could have caused them to settle.

If the post isn’t rotting, the concrete footing it’s on is almost certainly sinking or has deteriorated. Compare the old footing’s dimensions with an engineer’s recommendations and current code requirements (see next section). To get at the footing, you’ll have to saw through and strip off the concrete floor covering it, then dig down one side of the footing until you can measure its length, width and thickness. The 7-1/4 in. circular saw we used won’t cut through slabs more than 2-1/2 in. thick. For cutting through thicker slabs, rent a 14-in. concrete saw fitted with a diamond blade ($70 per day). Hang plastic sheeting to block migrating dust.

Our floor sagging occurred because the post bottoms had rotted and the footings were undersized. Besides pouring new footings and restoring the posts, we added plinth blocks to elevate the wood above moisture on the basement floor.

You’ll Need Expert Advice
Posts and footings support the weight of your house, so you have to size them right. Consult with a structural engineer, local building officials and contractors who specialize in this work. Hire the professionals to review all aspects of your project and provide the calculations and drawings necessary to obtain a building permit (Fig. A). Look for listings in the Yellow Pages under “Engineers, Structural,” and interview those who do residential work and have experience with this type of project. Expect to invest a minimum of $350 to have them:

Evaluate soil and its load-bearing capacity.
Examine your house to identify possible problems from jacking it.
Calculate proper footing, beam and post sizes.
Review your work plan. Show them the jack, shoring posts and spreader boards you intend to use to make sure they’re sized to lift and safely hold your house beam.

Prepare for Lifting and Shoring
Repair or replace posts or footings by raising the beam with a hydraulic jack and 4x4 post, then shoring it with adjustable steel posts. Buy a hydraulic jack ($35) and rent the shoring posts ($20 apiece per week) for the project. If you’re removing and resetting more than one basement post, use one hydraulic jack and move from station to station as you install and later remove the shoring posts.

CAUTION:
As a house beam is raised, any rigid plumbing, gas, electrical or heating lines in the basement connected to the beam, the floors or walls above could rupture. Before jacking the beam, release the connectors holding these lines and support them with lumber resting on the basement floor.

To monitor the total rise during lifting, measure and write the floor-to-beam heights on the beam where hydraulic jacks will be placed. Then remove or cut any nails, screws or straps that join the posts to the beam.

Heavy Lifting Calls for a Solid Base
To avoid cracking the basement floor, lay two “weight-spreader” boards under hydraulic jacks and shoring posts. Place the boards flat and level to ensure a safe lifting base for the jacks and posts. If you have a concrete floor less than 2 in. thick, ask the engineer if you should substitute thicker lumber to prevent floor cracking. Check along the cut edge of the concrete floor for voids that would collapse under lifting pressure. If you find any, ask the engineer for remedies to the problem.

Jacks apply tons of hydraulic force to lift the wood jacking post and beam, so select a virtually knot-free Douglas fir or Southern yellow pine 4x4. Don’t use 2x4s or weaker woods like cedar or redwood. Use a 6x6 if you’re jacking houses with two or more stories. Once the spreader boards are laid and the hydraulic jack is set in place, cut the 4x4 to length. Measure the height between the support beam and the top of the jack’s lowered piston, then deduct 1/2 in. and cut the post to length.
Snug up the 4x4 to the beam and position the shoring post. Now you’re ready to lift.