In every area of its homes, Bethesda Bungalows makes as many sustainable choices as allowable within the client’s budget. For foundations, the builder typically turns to one of three methods, each with varying levels of sustainability. “Bethesda Bungalows is leading the way on insulated walls,” says Andrew Bartley of the builder’s foundation subcontractor Bartley Corp. “They are on the forefront of it.”
For KellyGreen, the house being featured in this series, Bartley used conventional methods, but, like all Bethesda Bungalows jobs, installed an eco-friendly mix from Lafarge that replaces 30% to 50% of the Portland cement with fly ash and slag. (The exact percentage varies based on outside temperatures; higher percentages cannot be used in cold conditions.)
An extra step Bartley takes at the builder’s request is to install 2 inches of polystyrene insulation below the entire slab, a step that adds an additional R-10.
The foundation is waterproofed by spraying EPRO EcoBase, a flexible membrane that is VOC-compliant and nontoxic while still providing a seamless bond. The foundation contractor also uses EcoBase II as a capillary break between the footings and the concrete wall to reduce the chance of moisture traveling from below the footing up the wall.
Finally, the foundation walls also feature EPRO’s EcoDrain-E dimple board to reduce hydrostatic pressure.
Among Bethesda Bungalows other go-to foundation options is ThermaEZE from CertainTeed, in which two layers of EPS foam surround the concrete, providing a wall assembly R-value of 9.2 to 11.4.
On its Incredibly Green Home, a demonstration house built in 2009, Bethesda Bungalows chose Thermomass, an R-20 insulated foundation. A reverse of ICFs, ThermoMass consists of Dow Styrofoam insulation sandwiched between two layers of concrete, all connected by high-strength fiber-composite connectors. The foam provides a thermal break while the interior of the wall acts as a thermal mass.
In addition to these efficiency properties, Bartley appreciates that you can see if there are any problems in the concrete, such as voids or honeycombs, and resolve them.
Regardless of foundation type, the builder installs dual drain tiles and sump pumps, one on either side of the footers, to accommodate the area’s high water table. It’s one of a number of extra steps the firm takes to ensure its green-built homes are efficient and durable.
Katy Tomasulo is Deputy Editor for EcoHome.