Over the past few years, we have turned to Durisol (now Nexcem) insulated concrete forms (ICFs) several times. They offer an attractive blend of sustainable features with the convenience of conventional methodology.
For the teachers’ union office project, we needed a short stem wall to raise the walls of the building a suitable height above grade. There is no basement, and the footing is a shallow, frost protected perimeter beam, so the stem wall is only 2 feet tall. Durisol blocks provided us with a solution that worked well for several reasons. The blocks have a high insulation value (R-21 to R-28), are made from a very high percentage of recycled content, and are produced within a reasonable distance of our building site. They form a 5.5-inch concrete wall, using much less concrete than a full foundation wall (typically 8-12 inches wide).
In addition, the blocks come in several widths which for this building meant that we could use the 14-inch wide blocks as the first course and 12-inch wide blocks on the second course, leaving us with a 2-inch lip on which we could rest our floor joists. By keeping the floor joists within the insulated walls, we minimize thermal bridging and simplify air tightness at this important seam.
The Durisol blocks are dry stacked on the footing and on each course, making them very fast to install. They can be cut with a regular circular saw when necessary, and take a wood screw very securely. For our curved foundation, we did not attempt to cut the blocks to match the curve. Rather, we set them so the inside edges were touching on the curve and used a site-mixed hempcrete to fill in the gaps.
A lime-cement plaster is used to coat the exterior of the blocks, and we used a water-based, no-VOC liquid rubber and a 100% recycled content plastic dimple mat to complete the waterproofing layers on the exterior.
While this foundation wall still has relatively high embodied energy (due to its cement content), its energy efficiency, the lack of foam products, durability and the ease of construction make it an excellent option.