Imagine, adding "energy" to the long-standing formula of key expenses—principal, interest, taxes, and insurance—to calculate how much money someone could potentially borrow from a bank to buy a home.

Imagine, a home's ability to capture savings in heating and cooling and electricity costs factoring into that house's relative value—including location, square footage, and other comps—in an appraisal for resale.

These two principles are what's driving Congress to consider changing laws around housing finance that could cause people, home builders, remodelers, and the real estate industry to change the way they think about "green" and "sustainable" home building.

Tomorrow, the conversation around the economics of affordable, green residential real estate construction changes:

Wednesday, October 19, at 2:00 PM ET,U.S. Senators Michael Bennet (D-CO) and Johnny Isakson (R-GA) will announce the introduction of a bill that would enable better mortgage underwriting, encourage investments in residential energy improvements, and reduce home energy bills. The Senators will be joined by Ross Eisenberg, Counsel on Environment and Energy at the U.S. Chamber of Commerce; Philip Henderson, Senior Financial Policy Specialist at the Natural Resources Defense Council; and a representative from the Appraisal Institute.

Under the Sensible Accounting to Value Energy (SAVE) Act, federal mortgage loan agencies would consider a homeowner’s expected energy costs when determining the homeowner’s ability to make monthly mortgage payments. The average homeowner spends more than $2,000 each year on energy costs – more than on either real estate taxes or home insurance, both of which are regularly accounted for in mortgage underwriting. The SAVE Act would address this blind spot, giving a more complete picture of the costs of homeownership and borrowers’ capacity to service debt. It would also enable homeowners to finance cost-effective home energy upgrades as part of their traditional mortgage, lowering their utility bills and creating consumer demand for energy-efficient homes and home improvements. The SAVE Act is predicted to create 83,000 new jobs in construction, renovation and manufacturing.

The bill has support from a broad and diverse coalition of real estate, business, building trade and conservation groups that will also attend the announcement. Groups in support of the SAVE Act range from the National Association of Manufacturers and the U.S. Chamber of Commerce to the Natural Resources Defense Council and the Alliance to Save Energy.

The Leading Builders of America, which has backed this initiative for more than 18 months, has started up a site called, aimed at "defending policies that encourage responsible homeownership."