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Replacing Giant Columns

Getting ready, redefining the task

Replacing Giant Columns

Getting ready, redefining the task

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    The author's firm had been hired to replace the bases of six 100+-year-old wood columns; engineer's inspections had indicated that the upper portions of the columns were sound, and there were other good reasons not to disconnect them from the roof structure entirely. As it turned out, much more was needed.

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    To temporarily support the porch roof while the columns were replaced, the carpenters built posts from 10-foot-long 2x4s and 2x6s.

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    To start, the assemblies were sheathed with 1/2-inch plywood. Full-length 2x4 strongbacks were added to the outside for rigidity.

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    Double-post assemblies were joined by top and bottom plates stacked two high in order to support the roof while work was being performed on the columns.

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    The original plan was to replace only the column bases. Accordingly, the crew installed structural steel clamp rings around the shafts and shifted the weight from the pedestals to the concrete porch using 20-ton hydraulic jacks.

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    Rings of bending plywood served to guide the cutting of the wood columns, which was done with reciprocating saws and circular saws.

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    When the bases were removed, it was discovered that the interiors were delaminating and that the columns would have to be replaced in their entirety.

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    After cutting away the bases, the crew placed cribbing under the shafts while awaiting the delivery of new columns.

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    Sheets of 3/4-inch plywood protected the lawn from the lift that was used to transport and place the new columns..

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    The lift was fitted with a site-made cradle for moving the columns.

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    Moving a column with the lift

Our company was called in to replace the bases of six large columns on the two-story porch of a Colonial Revival house in Bernardsville, N.J., 30 miles outside New York City. The column shafts had a diameter of a little over 27 inches and a circumference of around 86 inches. Installed when the house was built in 1907, they were showing degradation at the bases, and there was some concern that they might be failing.

The original plan was to replace just the bottom portion of the columns. An engineer’s inspection revealed no problems with the upper shafts, and there were good reasons to avoid pulling entire columns. In particular, the two end columns were tied into second-story porches at mid-height. One of these columns had a concealed structural post supporting a porch beam, and both of them interrupted the outside corner of a large entablature, whose moldings were all scribed into the flutes. Plus, there would be roofing and flashing intersections to rework. While the four middle columns would be easy enough to replace, the two end columns would surely prove challenging.

Providing Temporary Support

The first step was to determine how the architrave — the beam supporting the porch roof — was built. After some investigative work and consultation with a structural engineer, we devised a method of tying the beam together with framing members so that we could jack and support it as a unit as we transferred the load from the columns.

Next we built five jacking “towers” (seeslide show), on top of which we placed 20-ton hydraulic jacks. The towers would support the architrave and roof, but we would also need to hold the weight of the columns. For this purpose, we had two-piece steel clamping rings fabricated by a local metal shop  By bolting these rings to the column above the cut line, we could safely support the columns while we worked on them. Once the columns were cut off and the bases removed, we planned to make templates for the replacement sections by tracing around the flutes. We would then block up the shortened columns until the new bottoms arrived from the millwork shop.

Best-laid plans. With two jacks per tower, the architrave and roof lifted easily, as did the columns. Cutting the columns proved more difficult. After making saw guides from bending plywood, we started in with a Big Foot wormdrive saw, hoping its 4-inch cutting depth would allow us to cut through in one pass. However, as we began to cut, the saw began to bind — it felt as though the inside staves of the laminated column were coming apart. We drove screws through from the outer layer into the inner layer, tying everything together. We abandoned the Big Foot and instead used a standard circular saw, finishing the cut with a recip saw.

Once the first column had been cut completely through, our suspicions were confirmed: The inner staves were delaminating because the glue was failing. The engineer advised that the columns would have to be replaced. We cut and cribbed the remaining columns  and suspended the job while the homeowners decided how to proceed. It was the end of September 2009.