A lally column, more often called an adjustable steel column or jack post, is a telescoping steel tube that adjusts upward or downward to temporarily support a weight from above, such as unsupported joists.
Typical Projects That Use Adjustable Columns
- Wall Removal: When a builder or home remodeler removes an interior, load-bearing wall, that person will insert a series of column in place of the removed wall to keep the house structurally sound. These posts will later be removed when the wall is rebuilt or other bracing is installed (such as a beam).
- Sagging Floors: Short jack posts are often placed in out of the way places like crawlspaces and basements to correct sagging floors.
- Temporary, Though Not Always: Adjustable posts are meant to be temporary, though often homeowners will leave them in permanently, particularly in basements or crawlspaces.
- Height Ranges: Adjustable columns range from about 3 feet to 14 feet tall.
- Adjustment Ranges: Within each class of adjustable steel column, there is an adjustment range. A typical adjustment range may be 7 ft 0 in to 7 ft 4 in (84"-88").
- Get Adjustment Range Right: Even though a post can be adjusted, you want to minimize elevation of the screw portion as much as possible as this adversely affects its strength.
- Height Affects Weight Rating: The shorter the column, the greater weight it will support. For example, a 6' long, 4" diameter column has a maximum weight rating of up to 21,300 pounds. Increasing the length of the column drops its weight rating to 10,200 pounds.
- Rent or Buy? While adjustable columns can be rented by the day, they are so inexpensive that it is usually more cost effective to purchase if you only need a couple of them.
- Use For Jacking: Columns are not to be used for the initial jacking. A jack should be used to elevate the item, then the steel column is inserted. After the post is in place, it can be used to make minute adjustments in elevation with the screw jack portion.
- Set Them Out of Vertical: Columns' weight ratings depend on them being mounted perfectly vertical. When a column is even a little bit out of vertical, you are in serious risk of injury or death as weight from above can force the post to shoot out.
- Use Without Steel Plates: Steel plates at the top and bottom of each steel column are necessary to prevent the cylindrical ends of the columns from biting into the wood.
A true lally column, according to David Brindle at Dean Column Co., is "actually a concrete filled steel column for permanent structural support. It was invented in the late 1800's by John Lally in Waltham MA."