How to Install a Jack Post

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Things You'll Need

  • 4-foot level

  • Safety glasses

  • Hammer

  • String line

  • 1/2 inch electric drill

  • 1 - 1/4 inch steel bit

  • 1 - 5/8 inch steel bit

  • 4 - 1/2 carriage bolts 2 inches long (or lag bolts--see step nine)

  • 4 - 1/2 inch washers

  • Adjustable wrench

  • If step 10 is needed -

  • 1 - 1/4 inch masonry bit

  • 1 - 1/2 inch masonry bit

  • 4 - 1/2 inch sleeve anchors - 2 inches long -


To make this operation easier, instead of a 4-foot level, use two magnetic torpedo levels and simply let them snap onto the post for steps 4, 5, and 6. For step 4 you may choose to clamp the top plate to the steel beam with either a 3-inch C clamp or vise grip pliers.


As always when drilling or hammering, wear protective eye glasses.

Jack posts are designed to provide adjustable leveling of floors and beams, both in new and re-modeling situations. Some are one piece while others are designed for either crawl spaces or full basements. Both styles provide top and bottom plates with one end equipped with a long adjustable screw bolt. You can expect to pay approximately 50 dollars, and they are readily available at most larger home improvement stores. In re-modeling situations, they are terrific for eliminating unwanted sags in older floors.


Step 1

Follow the manufacturer's assembly instructions for your desired length. In the case of one-piece posts, make sure that your post is short enough to allow for the adjustment screw to extend. Two-piece posts will have through bolts provided to adjust for either a crawl space or full basement. In addition, make sure that you have selected a position below your work area that has either a substantial concrete floor or concrete footing.

Step 2

Stand the post vertically below your work area to be jacked. It is always best to distribute the jacking force over a broad area rather than a single spot. This is accomplished by placing the jack under either an existing beam or providing a beam long enough to service the area. In some cases you may need a post at both ends for occurrences in the middle of a room where no beam exists.


Step 3

Place the top steel plate provided with the jack on top of the screw bolt and begin to crank the screw with the crank rod, also provided. At this point you only want to snug the fit. Do not begin lifting at this time.

Step 4

Place the 4-foot level against the post in the same direction of the post. Observe both the top and bottom windows. If you have never used a level before, you will need to tap the bottom of the post with the hammer in such a direction that lets the bubble move to the middle of both windows. Make sure that the top of the post remains under the beam and does not wander.


Step 5

Move the level 90 degrees away from your initial placement and repeat the tapping process in step 4.

Step 6

Move the level back to the first location and again tap the bottom of the post. You will note that the windows that were in line are no longer aligned. You will need to reposition the level several times between the first and second locations, tapping the bottom each time. Repeat this until the bubble remains in the center as you move the level back and forth. The post is now straight...this is essential for safety.

Step 7

Begin cranking slowly. If you are under a long steel beam, you will need to either sight the sag as you lift by going to both ends and actually observe the lifting action. If you have a helper, he or she can actually watch and direct you in the cranking action till the beam is level. If you are alone, you will have to check several times yourself. This is made easier by placing the string line tight along the beam's length enabling you to observe the jacking yourself as you crank.


Step 8

When you believe that the beam or sag is now level, place the level horizontally under the beam and observe the center window. If it is directly in the middle of the two lines, you will confirm that the jacking is complete. Better still, you should go to both ends of the beam and look along the bottom of the beam. If you still see a need to crank till it is straight. Four-foot levels only read accurately at that spot, so you need to confirm that the entire length of the beam is straight. You can also satisfy yourself that a sagging floor in a remodeling situation is corrected satisfactorily by actually walking on that floor, looking at it from different locations and placing the level on that surface itself.


Step 9

You may choose at this point to attach the top plate of the post to the beam. If your beam is steel, wearing your safety glasses and using the drill and 1/4-inch bit, drill pilot holes through the top plate holes into the beam. Then change to the 5/8-inch bit and widen each hole to receive the 2-inch carriage bolts and washers. Tighten with the adjustable wrench. This will ensure that the post is not nudged out of line accidentally. If your beam is wood, use the lag bolts.

Step 10

If the bottom plate of the post is resting on a finished concrete floor, repeat steps 8 and 9. Most bottom plates do not have holes pre-drilled. Therefore you may need to drill through the steel plate using the metal bits and then change to a masonry bit in order to drill into the concrete for the sleeve anchors. Insert the sleeve anchors and tighten. If your post is resting on a footing that will later be covered with concrete, no further actions are needed.


references & resources

Phil Mariage

Phil Mariage has produced and hosted his own public radio program for more than nine years.He holds a Bachelor of Arts in philosophy from Olivet Nazarene University and has worked in construction management since 1971. He was elected to three terms on his local school board. His writings appear at