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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. KeithH | | #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. cussnu2 | | #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. brendanalbano | | #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. KeithH | | #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.

  4. user-6929586 | | #7

    I'm in the Pitkin County working group for this topic. I thought I should share after coming across your article via a link from the "One Big House" film. You may want to revise your article based on these additional facts. I'm sure you would agree that accuracy is a key to quality journalism.

    "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."

    There is some inaccuracy in this quote that August Hasz of REG clarified for us. Please see the following from August:

    All- I have not been involved in the on going discussions that reference the data crunching REG did with the numbers provided by Holy Cross and Black Hills and it looks like a little confusion might be brewing. To help to attempt to sort this out here are a few key points to consider:
    • Math term for the increase rate in energy use: The term ‘exponential’ may have been thrown around a bit flippantly when the shock of how energy use climbs with home size was first highlighted, I’m honestly not sure. The term exponential is not in our report, and is not accurate. It is accurate to say the energy use per sq. ft. of home continues to increase in the data provided. (The only exception to that is a slight turn down in the last bin of data, and the magnitude of the decrease if minor.) What is shocking here is that intuitively one would assume energy use per area should decrease as home size grows, not increase. Larger homes have greater area per user, are often occupied less days per year, and often have less exterior building envelope per floor area— all of these factors should reduce the energy use per area as the home size grows.
    • 7,200 sq. ft. Is not a specific number in this data set. In fact, there is no specific point at which we see a drastic change, just a steady (and fairly steep) climb in energy use per sq. ft. with increasing home size. I think that was a number that showed up in a early much smaller data cluster and it should not be referenced any longer.
    • Increasing energy use with increasing home size. I want to repeat that again, because it is the key take way from our analysis, and too some degree only conclusion that can be solidly drawn. It is worth noting though, that when you combing the increasing rate per area with increasing area, there is a multiplicative effective to the increase. (Sorry couldn't help but throw a little math terminology back in.) Richard mentioned that the rate of increase is decreasing at the higher end of the range. That is accurate, however the trend is still an increase where common sense would have predicted a decrease in energy per area. To analyze the rate of change here is getting a bit too detailed for the scope of this study.
    • The reasons for this increase is not known, and cannot be determined from the data in this study. This data is for entire properties, presented in an anonymous format. One property might have a pool, another one in the same group by area might have a 25kW solar array and no exterior energy use. I included a section on speculation of causes. Those may or may not be true, at this point it is all speculation that should be investigated further to sort out the real causes. That study may acutally lead to reduction of energy use— this study is only just clearly identifying the problem.
    • Careful of conclusions drawn. Since we know that many of these larger homes have exterior energy use —and we know that the REMP program works to address exterior energy use— I feel it is not appropriate to attempt to read too much into this data. The key point was addressing a very common concept that I have seen discussed in many times: big homes are not assumed to use more simply because they are unoccupied, or lightly occupied per area and from that incorrect conclusion many people aren’t concerned about the energy use of larger homes.
    • Average energy use intensity. When we helped determine a value to use in the proposed revision to the REMP spreadsheet to account for energy from home size, the number used in that calculation is lower than the average for the entire data range AND is slightly lower than the energy used for the average 5,000 to 6,000 sq. ft. home. This home size energy accounting is only being applied to the area of a home that is greater than 5,000 sq. ft. (In that proposed REMP revisions). I felt it was crucial to use a conservative number and let the remainder of the REMP spreadsheet account for exterior energy use. Therefore, the energy used per area that is greater than this point is not accounted for. For example, if a 5,000ft2 home uses 75kBtu/ft/yr and a 10,000 home uses 104 kBtu/ft/yr, that calculation will only account for the area over 5,000ft2 at the same value per area as the 5,000ft2 home, the energy use in the calculation does not increase with home size. While it was the BOCC’s request to account for all energy, this data does not allow us to draw a concrete enough conclusion and care must be taken to avoid ‘double dipping’ and accidentally account for exterior energy use in two ways.
    • Home age. The way this data is formatted does not allow conclusions to be accurately be drawn relating to age of the home. Not good, not bad, just simply not enough info to make a conclusion on how the age of a building relates to energy use from the data as provided.
    • Politics of the changes. REG is providing technical support and advice for this effort, we are staying out of the good and bad judgments as much as humanly possible. I have heard it said we ‘want’ one thing or the other. We are doing our very best to work as strictly a technical adviser here.
    • Home size cap. I have also heard that somehow this report stated there should be a home size cap. That is completely in correct. (See my point just about this…)

    And the Pitkin County Chief Building Official is Brian Pawl, not Rawl.

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