Things You'll Need
Pencil and paper
Heavy-duty telescoping screw jack
New porch post
4-foot carpenter’s level
Power drill and bits
3-inch stainless steel screws
Porch columns are important, hardworking structural elements that not only shoulder most of the load of a porch's roof, but they also play a big role in defining the style of the porch. It's essential to replace a column that shows signs of rot or damage, but you may also want to replace your columns with more stylish versions just to bring a fresh new look to the exterior of your house. Either way, you'll be ensuring the long-term integrity of the porch as a whole.
Measure the length of the existing post and write this measurement down.
Position a telescoping jack as close as possible next to the column. Raise the jack, so that it elevates the beam 1/4 inch.
Cut through the middle of the post with a reciprocating saw to make two separate vertical cuts, one 8 inches above the other. Knock out the section between the cuts with a hammer.
Pry out and remove the top and bottom sections of the post with a crow bar.
Mark the center point of the porch column on the underside of the beam. Use an angle square to draw a centerline across the width of the beam.
Hang a plumb bob from the center point on the beam. Mark the center point on the porch deck under the plumb bob.
Draw a centerline through the center point on the deck, to match the centerline on the underside of the beam.
Cut the new column with a handsaw to match the length of the old column. If the column has a base and cap, you'll need to subtract their heights from the measurement before cutting. Attach the base and cap, if any, to the new column.
Mark the center points on the top and bottom of the new column. Draw centerlines through each center point and onto the side of the column. If you're using a base and cap, mark the centerline on the sides of each.
Position the column so that top and bottom centerline marks are aligned with the centerlines drawn on the deck and the beam. Check that the column is plumb with a 4-foot carpenter's level.
Lower the telescoping jack. Do this slowly to avoid knocking the column out of alignment. Check for plumb again, with the beam resting on the column.
Drill pilot holes for 3-inch stainless steel screws, and screw the column to the beam and deck on all four sides. If you've chosen a column with a cap and base, secure them to the beam and deck instead. Cover the screw holes with wood putty, sand flush when dry, and paint to match the column.
Rot or decay in a porch column may be evidence of a larger problem. If the column is significantly rotted, check your porch roof for leaks, and probe the beam and deck boards with an awl for signs of pervasive rot.
It may be difficult to match an existing damaged porch post. If you want the new porch column to fit in with other existing columns but can’t find the same style, you can order custom-turned columns or posts from a local lumberyard.
If the column supports more than just the porch roof, such as in the case of a two-story porch, consult a structural engineer before attempting to replace the column.