Energy consumption by jumbo houses is prompting one Colorado county to consider reducing the maximum allowable size of a new house below its current cap of 15,000 square feet.
The limit could be rolled into a revised energy code for Pitkin County, which includes the wealthy ski town of Aspen where large houses are not hard to find. The Aspen Times reported earlier this month that there appears to be at least some support for lowering the maximum house size among the county’s five commissioners.
One impetus for a smaller house size is a study from the Resource Engineering Group that found energy use rises exponentially when the size of the house exceeds 7,000 square feet, possibly because of all the amenities that typically go along with a big home.
“The common expectation is that as a home increases in size, the energy used per area (per square foot) of home will decrease,” the report said. “Anecdotal evidence has previously shown the opposite.”
The firm discovered that energy use per square foot goes up three times faster than total square footage. “Put another way,” the report said, “a 10,000-square-foot home doesn’t use 10 times more energy than a 1,000-square-foot home, but instead uses 30 times more energy.”
Working with data from energy providers for 900 homes over a four-year period, the study’s authors found the average energy consumption for all homes was 80,000 Btu/square foot/year (kBtu/ft2/yr). For homes between 1,000 and 5,000 square feet, consumption was 46 kBtu/ft2/yr, rising to 95 kBtu/ft2/yr for houses in the 5,000 to 14,000 square foot range. Energy consumption for the smallest homes studied (1,000 square feet) averaged 34 kBtu/ft2/yr, while 14,000-square-foot houses averaged 105 kBtu/ft2/yr.
In speculating on possible explanations, the authors listed features like snowmelt systems, roof and gutter melt systems, pools, spas, complex audio visual and security systems, a liberal use of glass in high-end residential construction, and “increased expectations of thermal comfort.”
Newer homes also are proving to be less energy efficient than older ones, the report said. “We would expect newer homes to be more efficient,” it said, “but on an energy used per square foot basis, the trend is the opposite.”
The energy use study counted 18 homes between 13,000 and 14,000 square feet, with a total of 75 houses measuring 10,000 square feet or greater in 2017.
House size is part of a larger discussion on energy use
Brian Rawl, the county’s chief building official, said the discussion about maximum house size is only part of a much broader review of energy and land use regulations in Pitkin County.
The county in 2017 passed a climate action plan aimed at reducing the county’s greenhouse gas emissions. The city of Aspen and Pitkin County adopted a Renewable Energy Mitigation Program in 2000 that seeks to offset the impact of outdoor features such as snowmelt system, spas and pools. Owners of houses 5,000 square feet and larger are required to pay a REMP fee or install on-site renewable energy systems.
“It’s a huge discussion going on right now,” Rawl said in a telephone call. “It’s a developing thing. There are no real answers yet.”
The county dropped the maximum allowable house size from 20,000 square feet to 15,000 square feet as part of the 2006 land use code, Rawl said. Most lots, however, have a limit of 5,750 square feet. In addition to paying REMP fees, lot owners who want to get to 15,000 square feet must buy transferrable development rights that help preserve public lands and remote areas.
At 15,000 square feet, a house is six times larger than the 2,426-square-foot median size of a new U.S. home in 2017. Rawl says not many 15,000-square-footers are built in a year, although the last couple of years have seen quite a few of 10,000 square feet and up.
If that sounds like a lot, consider that Pitkin County has one house measuring 55,000 square feet. The dwelling, once owned by a prince of Saudi Arabia, comes with a 19-car garage.
Annual community surveys also show support for capping house size. The Aspen Times said the 2018 Pitkin County survey found 71% of the 518 respondents rated limitations on house size important; 48% said size limitations would have great benefit.
County Commissioner George Newman said any final decisions on house size or other energy code revisions are still months away. “I don’t see anything changing until, at the earliest, the end of the year,” he told the newspaper.