ICF Foundation with Stick-Framed Walls – GWC Mag

Our company, Just Housing, creates repeatable and scalable high-performance designs and assemblies for cold climates. Our approach can be modified when projects call for adaptation, but our design strategy doesn’t change. Our goal is to create cost-effective, durable, and energy-efficient enclosures using familiar, readily available, non-proprietary materials. In this article, we will share our go-to foundation and framed-wall assemblies, and then talk about how we modify them for different contexts without compromising quality, cost, and performance.

High-performance foundation, fairly conventional walls

We use insulated concrete form (ICF) systems for their ease, versatility, and speed. The concrete slab is poured over a polyethylene vapor retarder, over two layers of EPS foam with staggered seams, over aggregate. Framed walls are stick-built 2xs with plywood sheathing sealed as the air barrier. The sheathing is wrapped in a nailbase (a layer of rigid foam bonded to plywood or OSB), then covered with a water resistive barrier (WRB) sheetgood installed shingle style, integrated with window, door, and base flashings. We specify steel siding for its durability and ability to drain bulk water effectively.

The ICFs go up quickly, and they can be used for basement walls, frost-depth footings, or shallow stem walls. We specify a standard R-22 ICF, but a higher R-value ICF could be used without having to change the overall assembly details. We call for the inner layer of the ICF insulation to be cut down 4 in. (pictured left), allowing the slab to extend over the core to provide a flat working surface for wall framing, and to make the continuity of the air barrier assembly easier to achieve. The slab serves as the air barrier in the foundation and is sealed to the framed wall with a bead of caulk at the bottom plate.

We use standard single-stud wall framing with…