how can i add a column to existing foundation

by Dominic
(houston)

Question:

how do i add a column to existing foundation to support a roof deck

Answer:
The function of a column is to transfer the load from beams down to the footing. I want to make this distinction because the wording of the question is technically incorrect.

Columns do not directly support roof deck or floor deck. In roof framing, the deck is supported by roof joists or trusses which transfer the load to a beam down to a column which pass it to the footing. In the absence of beams and columns, the load goes from roof deck to roof joists to bearing walls down to the footings.

To add a column to an existing roof, there must be a beam that will not only collect the load but will provide the point of transfer for column. For a beam to work at this type of application, it must be supported on both ends either by columns or walls.

In new construction, usually the column is installed first followed by beams, joists, deck, before roofing. When working on existing roof, the procedure may be reversed depending on accessibility and availability of tools to bused. Once the beam is installed, temporary post or wall can be installed to hold the beam in place while the work on the new column is being done.

Supposed the new column is added in order to remove an existing wall to free up more space. The only way this can be done is to replace the wall with a beam and column. First install two temporary walls on either side of the existing wall. Next, remove the wall and install the new beam.

Sometimes due to the heavy load being transferred to the column, a new footing may be required. Suppose the wall you're replacing is 20 ft long. Suppose the total load along this wall is 1000 pounds per foot. When the wall is being replaced with a beam you're transferring 10,000 pounds to the column. This heavy load can easily crush the concrete slab, that's why a new footing is necessary.

Installing new footing at existing concrete slab is no easy task. It often requires demolition work to remove concrete and dirt to allow space for new footing. Installing temp walls to support the roof will work well because it will provide needed time space to do extra work prior to installing the column.

Depending on the type of column and how big and heavy the column is, it may work to your advantage if you install the column, hold in place before pouring the footing. This is one of the options that need to be considered when you're working at an existing structure.