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)

The most obvious improvement offered by using ICFs is the addition of insulation. Concrete has a very low R-value (an 8" thick concrete basement wall would typically have an R-value of approximately 0.75; even less than a single-glazed window with an average R-value of 1.0). So concrete walls offer very poor thermal performance. Even in the summertime, a concrete basement wall will be cool to the touch, because of this. Adding even a small amount of insulation to the concrete wall makes it better, and ICFs provide a good way of getting an insulated concrete wall.

This article is going to be somewhat less useful to owners of existing homes in general, since installing foundation walls is something that is usually only done in new construction. But understanding a bit more about how foundations work can help when it comes to improving the performance of an existing basement space, as well.

Contractors like them because they reduce labor costs. In typical construction, concrete walls are built by setting up reusable forms which contain the concrete and mold it into its finished shape. The forms are heavy and hard to install because they have to be strong enough to support the weight of the wet concrete and hold it in place for a period of several days to a couple of weeks, until the concrete has cured. Then, workers must be sent back to remove the forms and carry them to the next jobsite. With ICFs, the blocks that are used are much lighter and are easily carried by one person, making the preparation of the forms easier and less labor intensive. ICFs also save after the concrete is poured, because the additional step of removing the forms is omitted. The ICFs are left in place as part of the building.

Early ICFs were basically two pieces of rigid insulation foam held together with plastic ties. This would result in a full thickness concrete wall with rigid insulation on both the outside and the inside. They were originally developed for the speed of assembly and the labor savings, and the insulation was largely an added benefit.

Eco-block is an example of this kind of ICF, although they also offer configurations with thinner concrete cores (as little as 4", which is still structurally sound). More recent versions, such as Insulock, use a block that looks like an oversized Lego made of polyurethane foam. These closed cell foam blocks are lightweight, and can be easily carried and quickly installed. The open cores of these blocks are then filled with a steel reinforcing rod and poured concrete to create a structural wall with properties much stronger than a wood stud wall, much less concrete needed than a traditional poured concrete wall, and much better insulation than either one. Depending on the required wall strength, it may not be struturally necessary to fill all of the cores with concrete, leading to even more savings in materials.

Having insulated foundation walls makes for a more comfortable and more energy-efficient basement. Even for concrete slab-on-grade construction (where the concrete slab floor sits directly on the ground), having insulated foundation walls helps keep the concrete floor at a more comfortable temperature, and keeps the cold from conducting through the concrete as readily.

ICFs are not only for basements. They can be used for walls above ground level as well. The Portland Cement Association has a website with further information about homes built with ICFs, and showing examples of very conventional looking homes that are built with walls constructed in this fashion.