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Green Building News

Colorado County Ponders Lower Limit on House Size

A study finds energy use climbs rapidly as house size increases, possibly because of amenities like snowmelt systems and spas

In Aspen, Colorado, county commissioners are discussing updates to energy and land use regulations, including a possible reduction in the maximum allowable size for a single-family house. The cap is now set at 15,000 square feet. [Image credit: Katie Haugland Bowen / CC / Flickr]

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.


  1. Burninate | | #1

    Why not tax energy costs to deal with this? If Oprah wants to relax in her outdoor hot tub amidst the snow, charging her through the nose for fuel & electricity and spending that money on solar panels (or rebating it in equal amounts per-citizen) seems like it makes a lot more sense than banning her or trying to scare off her contemporaries who want to move nearby.

    1. Keith H | | #5

      I'm with Burninate here. Solve excess energy use by the ultra wealthy by capturing carbon costs. Capturing these carbon costs will also create efficiency opportunities. While I don't know how you make a big driveway melter more efficient, there are a lot of options for power generation on site and up and coming options for storing that energy.

      Banning certain size homes will just shift the problem without creating efficiency opportunities.

  2. But Why? | | #2

    “increased expectations of thermal comfort.”

    In other words, God Forbid someone with the money to do so set THEIR thermostat in THEIR home wherever they damn well please. It wont be long before AOC and the green weenies propose a final solution for people like this.....

  3. Trevor Lambert | | #3

    “The common expectation is that as a home increases in size, the energy used per area (per square foot) of home will decrease,”

    Why would that be an expectation? I tried, but failed, to think of a single justification for such a belief. All other things being equal, a house with a larger floor area will have an equally larger surface area. I would expect that, again all other things being equal, that a larger house would use less energy per volume, not area. But since we don't measure house sizes by volume, that's irrelevant.

    Aside from what's mentioned in the article, here are a couple of other factors coming in to play when you're comparing a modest house to a super mansion:

    1. Ceiling height. No super mansion is going to have 8 foot ceilings. They're likely going to be at least 12, maybe even 16 feet. So surface area per floor area is going to be higher.
    2. Architectural complexity. Super mansions are going to be replete with "nifty looking" outcroppings, nooks, crannies, crazy roof lines. All of these add either surface area, or air leakage or both.
    3. Owner behaviour. The average person cares about their energy bills, and will modify their behaviour somewhat because of that. Someone who makes hundreds of thousands of dollars a week, or day, doesn't give two Fs. A $5000/month energy bill to them is equivalent to less than a penny to you or me.

    1. Brendan Albano | | #4

      I don't think a larger footprint gives an equally larger surface area. For example:

      10' x 10' x 10' structure:

      - 10*10 = 100 SF floor area
      - 10*10*4 = 400 SF wall area
      - 10*10 = 100 SF roof area

      A 20' x 10' x 10' structure:

      - 20*10 = 200 SF floor area (100% increase)
      - 10*10*2 + 20*10*2 = 600 SF wall area (50% increase)
      - 20*10 = 200 SF roof area (100% increase)

      1. Keith H | | #6

        I think Brendan is correct about the economic of perimeter. I also think Trevor is correct. I'd add if you want the ultra wealthy to worry about the cost of energy, you need to make it a regulatory matter (btus per sf, etc) rather than banning what they want to build.

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