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By Cheryl in Ft. Collins, CO on 9/23/2009
I am seriously considering a modified slipform construction technique for the walls of my carriage house project, which is 24x42 with a small apartment above near Ft. Collins, CO. I have a lot of stone on on the property that is block-like rubble that would be utilized. The walls would best be described as steel-reinforced concrete with a rock face. Would love to hear from anyone who has real knowledge of this technique and get advice on how to do it green, strong and as economically as possible. My two strong sons, 23 and 24 yrs. think we can do most of the labor ourselves. My Dad will help with the electrical, and I will learn how to install PEX. So this is a real owner-builder project.
The slipform information I have is from a book I ordered on slipform construction called "Living Homes Integrated Design & Construction" by Thomas J. Elpel.
Here are some excerpts:
"Slip forming using beadboard panels is similar to traditional slip forming. The footings are built the same, except extra width is necessary for the beadboard panels. Advanced Foam Plastics offers a 5 1/2" polystyrene beadboard attached to 1/2" of oriented strand board (OSB). Slip forms measure 2'x8' plus a couple of small fill-in forms.
The cement and rock portion of the wall is 9" thick, and the insulated panels add another 6", so the total wall is 15" wide. That 15" wall needs an additional 4" for the slip form on the outside, and an additional 4" ledge for the beadboard panels on the inside. This brings the total width of the footing to 23".
The space between the beadboard panel and my exterior slip form was 9". Spacers cut to this length made tightening the forms much easier. With rebar and spacers in place, and the first beadboard panels in place, you are ready to wire-tie the slip forms to the panels. Stones are placed inside the forms with a good face against the plywood, and concrete is poured behind them.
It was my experience, that in the fall, with moderate temperatures, the concrete and rock combination set up sufficiently in 5 hours. At that time, we carefully removed the forms and chipped out what cement was not desired, then left the cement alone to continue to cure overnight.
The next day another form is supported in place on top and the whole process starts over. "
As to snow loads and wind, I know that the property is at 7,050 feet so needs to withstand 40 psi and 130-140 mph wind. My other big concern is to make the whole structure as fireproof as possible. So, looking at steel joists and trusses and some kind of fire-resistant green shingles. I am very open to your suggestions concerning smarter, more efficient, less expensive, environmentally friendly etc. design and material. This is my "learning project" before I build the house.