Precast Foundation Walls

April 9, 2007

Last week I wrote about insulated concrete forms (ICFs) as an alternative to traditional poured concrete walls. The ICFs I mentioned would serve to reduce at least 50% of the concrete used, compared to a traditional basement wall. (The Eco-blocks, with a 4" instead of an 8" wall would be a 50% reduction. The Insulock block system, with it's cylindrical cores filled with concrete, uses even less.)My article prompted Lloyd Alter at Treehugger to write a response where he took a different view of ICFs. Some of the concern about using ICFs is that they are still energy intensive. Concrete is an energy intensive material to produce. Using less of any energy-consuming material in construction is preferable, and is one of the goals of green construction. But in most cases, the energy used over the life of a building is more than the energy that goes into the making of the materials and their assembly.

All of this leads to yet another product for foundation walls I had already been planning on writing about: precast concrete walls. I was introduced to these on a project I was working on late last year, and I have been interested to learn more about them. Superior Walls manufactures a wall that has just 1.75" concrete (plus a bit more in vertical ribs spaced every two feet along its length). That means it is only using about 20 percent of the concrete used in a standard 8" concrete foundation wall. Superior Walls panels also incorporate rigid insulation in the panels, so that they have an R-value significantly higher than solid concrete. Furthermore, with the ribs, the panels are cast in a configuration much like stud walls. This allows finished basements to be easily constructed, and with only a little pre-manufacturing coordination, electrical and plumbing services can fairly easily be accommodated into the walls. The walls can also have additional insulation installed between the ribs, very much like stud walls.Superior Walls are also manufactured in a controlled facility and then delivered to the site and installed by crane. This is similar to the manufacture and delivery of pre- manufactured houses or structural insulated panels (SIPs). The benefit of controlled manufacturing is that much closer tolerances are possible. The walls can also be erected quickly (typically in just one day) and construction of the structure above can proceed almost immediately, rather than needing to wait for the concrete to cure before construction can continue.

If you are going to provide a basement for a building, it makes a lot of sense to provide it with an energy efficient foundation wall, as much as the rest of the building needs to be energy efficient, as well. Putting a well designed, efficient structure on top of an old-fashioned poured concrete or CMU foundation wall is something like a championship athelete putting on a ratty old pair of workboots before competing. You may have great stuff up above, but if the basement is going to be conditioned (and basements are almost universally conditioned spaces in contemporary construction) it should be more efficient than plain concrete. Both ICFs and precast walls will provide much higher levels of performance and help to reduce energy consumption, and at the same time, they will use less concrete than a comparable foundation of solid poured concrete. All of these systems are also going to help produce a more comfortable basement, which can then more readily be used as living space.

[4.10.07 Edited to add:] As a part of this ongoing discussion, Lloyd Alter has written another piece for Treehugger about foundations, and questioning how much is needed. Lloyd and I seem to have set up an informal discussion about the topic between the two of us with this series of articles, and I would be very interested in hearing your thoughts and reactions on the topic. Articles:Insulated Concrete Forms (GreenOptions)Insulated Concrete Forms: Another Opinion (Treehugger)Precast Foundation Walls (GreenOptions)What Lies Beneath (Treehugger)