Contrary to what you might hear from others, Passive House certified buildings can be built on any type of foundation. Insulated slab-on-grade foundations are usually the most cost effective, but we also offer full foundations, crawl spaces, and foam-free pier foundations, each of which can be detailed for Passive House performance and comfort.
Our proprietary system for concrete slab-on-grade foundations is a raft slab, the Ecocor Passiv Slab. Made from borate-treated EPS (expanded polystyrene), the most durable and benign plastic foam for this location, we designed the parts and pieces to lock together like Lego blocks—protecting the concrete slab from thermal loss, isolating the interior from radon and water vapor, and acting as a concrete form—all in one system.
Once the raft slab insulation is placed, we pour an 8 inch steel-reinforced concrete slab—thick enough that separate footings are not required under point loads. It is then polished and sealed as a finished floor, or covered with another material.
For projects where treading lightly on the land is a key concern, eliminating plastic foam is a goal, or access to the site is compromised, we offer a pier foundation system. Using helical piers—galvanized metal posts with an auger screw at the bottom, literally drilled into the ground—we minimize disturbance of the site. The floor is framed with deep I-joists and filled with dense-packed cellulose, with an airtight, moisture-repelling skin applied to the bottom of the floor system.
We use a small, insulated chase to bring utilities into a central location. The same insulated floor system that we use for piers can be used on an uninsulated foundation or crawlspace.
Our foam-free framed floor system uses 16"- 24” I-joists filled with dense-packed cellulose, with assembly insulation values of .1 W/m2K (.018 hr/ft2 F/BTU) ~ R 58 to ( of 0.070 W/m²K (0.012 Btu/hr ft² °F), ≈ R 81. Depending on the situation.
Let us be clear:
YOU CAN BUILD A PASSIVE HOUSE WITH A BASEMENT!
It won’t be the “practically free” storage space that typical 1950’s style construction provided, but our Passive House basements are also not cold, damp, or moldy like those 1950’s basements, and they can be used safely as living space.
There is a cost to waterproofing and insulating the foundation to a degree appropriate for a Passive House, but it can be done—we know, because we have done it on multiple occasions—most often when the building site is sloped and the basement can be a “walk-out” on at least one side.