The frost depth for this location was 4 feet, so we excavated to exactly that depth below rough grade. With the extremely sandy Cape Cod soil, it made sense to excavate each footing separately. To set the footings, we had to maintain two critical parameters: The 11 footings all had to be set at exactly the same elevation, and they all had to be in a perfectly straight line. After the footings were placed, the crew used the fittings to attach the post connectors. Setting The Footings At The Same HeightĮach footing has an integral fitting for an eyebolt that was used to lift and place the footing. When the footings were delivered on site, we were ready to begin installation. Each footing was 5 feet tall and 1 foot in diameter at the top and tapered slightly down to a wide supporting base that was about 30 inches wide and a foot high.
The perimeter of the porch required 11 footings along the long section and five additional footings where the porch returned around the corner of the house. Eventually, these threaded fittings would be the attachment points for the post-base connectors, a critical link in the framing sequence. In the casting process, the manufacturer embedded a fitting in the top of the footing that could accept a threaded eyebolt for lifting and placing the footings. So Botelho asked the precast manufacturer to start casting the footings in the round. But setting a straight line of footings presented a big enough challenge in itself trying to align the square edges was an additional task that could be eliminated if the footings were cylindrical. When Botelho started using precast footings a few years back, they were typically made with square tops. For these reasons, Botelho suggested that we go with precast footings. If the soil is at all moist, the tube material can absorb moisture and deform before they can be filled. Another consideration when using site-poured tube footings is that they have to be inspected prior to filling, which can often mean a day or more between the placement of the forms and getting them filled.
And backfilling tube footings almost inevitably causes the tubes to move a little (and sometimes a lot), which results in a ragged layout. The first factor is that they are difficult to install with precise alignment, which was critical to this project. Poured concrete footings pose a number of challenges. In reviewing the project with the site contractor, George Botelho, we considered a couple of options for the porch footings: the typical poured-in-place tube footings vs. In addition, the project was located in one of Cape Cod’s high-wind zones, so the alignment of all the support and framing components was a critical structural detail specified by the engineer to resist the uplift potential of the large porch roof. Because the roof was to be a prefabricated truss system that was ordered about the same time as the footing installation, there was little margin for error or for misalignment of the footings. The porch and its roof framing system had to be supported by 20 footings total-16 perimeter footings plus four inside footings to support the wider porch section at the end of the house the long side of the porch had 11 footings. The home was to have a 1,100-square-foot covered porch that measured 78 feet along one side and wrapped around one corner of the house, and many of the standard construction details required an exceptionally high level of precision. That was the challenge that Shoreline Builders, of Scituate, Mass., faced recently when building a new, custom, high-performance residence on Cape Cod. That seems easy enough, but things get a bit more complex when the straight line is 78 feet long and there are 11 points along the line that have to be lined up perfectly. They say the shortest distance between two points is a straight line.
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