Lally columns and jack posts are vertical steel members that are used to support horizontal members like ceilings and beams.
However, there are important differences between these two vertical members which, if ignored, can be disastrous for any structure.
Differences between Lally Column and Jack Post
Here are the differences between the lally column and jack post:
|Characteristic||Lally Column||Jack Post|
|Purpose||Provide temporary and permanent support for horizontal members||Serve as temporary support for horizontal members and correct sagging|
|Height adjustment||Fixed height||Can be adjusted after installation|
|Load-bearing||Withstand vertical loads only||Support horizontal and vertical loads|
They are commonly used in crawl spaces and basements and have well-defined standards for their load-bearing capacities.
Wooden and concrete structures are sometimes used as lally columns, but they offer less resistance to vertical loads.
Additionally, the durability of wooden lally columns can be a concern if it's exposed to the elements.
In contrast, concrete lally columns are durable, but due to their brittle nature, they are prone to failure.
Therefore, never use plain cement concrete (PCC) to build a lally column.
On the other hand, jack posts are made up of hollow cylindrical steel pipes and an adjusting screw.
Their height can be adjusted even after installation.
Generally, the material used to make jack posts is low-carbon steel.
Additionally, their lengths range from 3.5 feet to 16 feet, with varying diameters.
While lally columns can be both temporary and permanent, jack posts are only temporary supports.
Lally columns also provide support to structural members like basement beams.
Jack posts, in addition to providing support, help in correcting the sagging of horizontal members and require periodic inspection.
It is also crucial to note that lally column heights are fixed, and no adjustment is possible after fixing it.
Generally, lally columns are made in different lengths ranging from 3 to 14 feet.
Their diameter typically ranges from 3.5 inches to more than 4 inches.
For permanent use, the diameter of a lally column should be greater than 4 inches.
Also, note that ASTM A53 Grade B or an equivalent grade of material should be used for a lally column steel tubing.
To meet IRC & IBC (International Residential Code and International Building Code) standards, the lally column should have a minimum thickness of 11 gauges or 0.120 inches.
Codes for Lally Columns and Jack Posts
The International Residential Code includes the specifications for lally columns under the sections R502, R407 & R802.
R502 of the IRC describes the fastening of lally columns.
In the case of jack posts, the USA has not yet standardized their load-bearing capacities.
However, BS 4074:2000 outlines the size, strength, and construction of jack posts or metal props.
British standards classify metal props into five categories based on their length.
In What Situations Should a Lally Column or Jack Post Not be Used?
A solid footing foundation is the first and most important requirement for installing lally columns or jack posts. If you do not have a strong concrete foundation, avoid installing these supports.
Moreover, even when your floor appears to be in good condition, supports may sink if the soil beneath it is not properly stabilized. This could lead to a structural failure and a serious accident.
Also, avoid lally columns and jack posts in flood-prone areas.
Furthermore, never use these supports if you have a sump pump in your basement, as they cause soil erosion and affect their stability.
How to Install a Lally Column
The installation process can be divided into two phases: the documentation phase, followed by the construction or installation phase.
Here is a step-by-step process on how to install a lally column:
Step 1: Preparation of Structural Report
A qualified and practicing structural engineer will identify your needs.
The engineer will also identify the structural conditions, load conditions, and other important factors.
Based on these conditions, he/she will suggest the size, numbers, and locations of lally columns.
Step 2: Getting Permits
In most states, you will need building permits to install lally columns permanently.
The approving agency will examine the structural report to verify your application for permanent construction.
Following claim verification, they will physically inspect your structure to determine the validity of your application.
In most cases, your contractor will assist you in filing claims and obtaining the necessary permits from these authorities.
Permissions are typically not required for temporary construction.
However, it is recommended that you check your local building codes to verify this.
After completion of phase one, i.e., documentation, you can move to the next phase of construction.
The documentation part is not compulsory if you only need a temporary lally column.
Step 3: Identification of the Location
Determine the best location for the installation of the lally column.
Identify a spot on the beam and drop a plumb bob from the beam to the floor and mark the location of the plumb bob's drop on the floor.
Draw a circle with a diameter of 12 inches, with the marked point in the center.
If your floor is made of concrete, use a hammer or concrete cutter to break the concrete inside the circle.
Step 4: Build a Strong Footing
A strong footing is essential for the erection of lally columns and proper disposal of loads in the ground.
Dig the floor up to two feet underneath the circle.
Mix enough concrete and fill this hole with concrete to the level of the actual floor.
Cure the concrete for the next six weeks for proper strengthening.
Backfill the sides with soil if there is any vacant place, and clear the topside.
Step 5: Measurements and Cutting of the Lally Column
Measure the distance from the bottom of the beam to the top of your concrete footing with care.
To compensate for the thickness of the plates on the top and bottom, reduce the measured length by the thickness of both plates.
These plates typically have 1/4-inch thicknesses.
As a result, you can directly reduce the measured length by 1/2 inch.
Now mark the resultant length on the lally column.
If necessary, carefully cut the lally column to achieve a smooth surface.
Step 6: Erection of Lally Column
Deploy a hydraulic jack right next to the location of your possible lally column. Lift the beam slightly, but not more than 1/4 inch.
Now center your lally column on the footing with plates.
Level your column vertically from two sides to ensure proper straight orientation.
After you've determined the best orientation, mark the location of holes in steel plates, drill them up to 2 inches in the floor, and beam to insert screw anchors.
Next, carefully erect the lally column with plates on top and bottom.
Pay close attention to the orientation of lally columns. It should be perpendicular to the surface and centered on the footing.
Finally, remove the hydraulic jack after proper erection and allow the beam to rest on the lally column.
How to Install a Jack Post
Jack post-installation is simple and various sizes of jack posts are available in the market.
Because it is considered a temporary construction, no special permit is required from any authority.
Step 1: Identification of Location
You need to identify the perfect location where you should install your jack post.
It may be under the sagging portion of horizontal members or under long-span crawl places.
Mark the locations properly to avoid any problems during the installation process.
Step 2: Preparation of the Floor
Jack posts transfer the load from horizontal members to the ground, so it's essential to ensure that your floor is sufficiently strong to support this load.
If you have a sufficiently strong concrete floor, you are ready to go.
In case you don't have a concrete floor, you need to build a strong foundation ahead of time.
The footing preparation process is the same as for the lally column.
Dig a 2×2 feet hole, fill this hole with concrete, and set it aside for 6 weeks to cure.
After the concrete has been properly strengthened, proceed with the installation process of your jack post.
Step 3:Measurements and Selection of Jack Posts
Measure the distance from the bottom of your beam or horizontal structure to the top of your footing surface.
According to this measured length, select the length and adjustment range of your jack post.
Step 4: Assembling the Parts
There will be two hollow steel cylindrical pipes, one with a larger diameter and the other with a smaller diameter.
Both of these pipes have carriage holes on one end. This is known as the carriage end.
Insert the smaller diameter pipe's carriage end through the larger diameter pipe's carriage end.
Grease your adjusting screw and insert it into the smaller diameter pipe's non-carriage end.
Keep your adjusting bolt at the bottom of the adjusting screw before fitting the screw in the pipe.
Step 5: Erection of Jack Post
At the desired location, place the flat side of the plate against the bottom of the beam.
Drop a plumb bob from the center of the plate to the ground and mark the location of the plumb bob's fall.
If you don't have a plumb bob, you can make one with a string and a key.
Maintain your bottom plate on the ground, perfectly centered on the dropping point and oriented with the top plate.
Place the column assembly vertically and keep the adjustable jack in the center of the bottom plate.
Move the outer pipe upward until it tightly touches the bottom of the beam.
Step 6: Finish your Installation
To make your post perfectly aligned in a straight position, insert the driving screws through the carriage holes of both pipes in two directions.
Maintain the column's straight position by vertically leveling it.
After that, using a suitable tool, move the adjustable jack bolt until it encounters its first resistance.
Your installation process is now complete.
When properly installed, jack posts can take loads from the beam and dismantle loads in the ground.
Once in a while, tighten the adjustable jack again.
How Much Does it Cost to Install a Lally Column and Jack Post?
The cost of installing lally column and jack posts depends on several factors, including support conditions, the span, length, and condition of existing horizontal members.
A lally column installation cost typically starts from $2500.
This cost rises as the number of columns and the size/span of existing and prospective beams increase.
On the other hand, a jack post installation typically costs between $10,000 and $15,000.
This price includes labor, jack post costs, and mobilization fees.
How Much Weight Can a Lally Column Support?
The load-bearing capacity of the lally column depends on its dimensions.
A short lally column can support more load than a long column.
For instance, a 6-foot-long, 4-inch diameter lally column can withstand a maximum load of 21,300 pounds.
A lally column with a span of 4 feet and an 8-inch diameter can withstand a maximum load of 27,200 pounds.
Decreasing the length and increasing the diameter leads to a higher load resistance capacity.
Aside from dimensions, the load-bearing capacity also relies on the strength of the top and bottom plates.
How Much Weight Can a Jack Post Hold?
A jack post can hold a load of 20,000 pounds to 32,000 pounds. Jack posts can hold the loads coming from sagging beams, porches, or roofs.
Frequently Asked Questions (FAQ)
Do Lally columns Need to be Filled with Concrete?
Lally columns are filled with high-grade concrete to avoid buckling.
If you are using a lally column to support light loads, then there is no need to fill it with concrete.
However, almost all lally columns available on the market come with prefilled concrete in them.
Can Jack posts be Permanent?
No, a jack post's diameter is usually less than 3 inches.
According to the International Residential Code (IRC), permanent steel columns must be larger than 3 inches in diameter.
Can Lally Columns be Used Outdoors?
Yes, lally columns can be used outside, but with caution. To prevent rusting at the base of the lally column, use exterior-grade paint.
It is also crucial to note that lally columns are designed to withstand vertical loads only, not horizontal or lateral loads.