Spray foam band joist

The key to having a low-energy house is to have a very tight envelope and a lot of insulation. This new construction in Concord uses spray foam in all the walls, which was shaved down to be flush with the wood framing. This photo shows one of the crucial points to air seal: the band joist. That's the place where the house foundation and the rest of the building meet. In most homes, this is a very leaky spot so closing it off is a good way to tighten up a home. In houses that are very air tight, such as this one, there is a mechanical ventilation system, called a heat recovery ventilator, to ensure that there's a steady supply of fresh air.