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Even if a small house has lower levels of insulation than a larger house, it's likely to cost less to heat. 1. R-19 walls, R-30 ceilings, double-low-e (U=0.36) vinyl windows, R-4.4 doors, infiltration of .50 ACH, and R-6 ducts in attic; 2. R-13 walls, R-19 attic, insulated glass vinyl windows, R-2.1 doors, infiltration of .50 ACH, and uninsulated ducts; 3. Natural gas at $0.50 per therm; 4. Electricity at $0.10 per kWh.

Having written about green building for more than twenty years now, I've encountered lots of misperceptions. One of those is that green building always has to cost a lot more than conventional building. There are plenty of examples where it does cost more (sometimes significantly more), but it doesn't have to, and green choices can even reduce costs in some cases. Let me explain. When someone is considering building a green home, my first, number-one recommendation is to keep the size down. Since 1950, the average house size in the U.S. has more than doubled, while family size has dropped by 25% -- so we're providing 2.8 times more area per person than we were back then. If you think you need a 3,000 square-foot house, consider whether 2,500 would suffice, or even less. There are some really great homes being built at 1,400 to 1,500 square feet -- homes where every square foot is optimally used and there aren't rooms, like formal dining rooms, that sit empty most of the time.

Often, because we're conditioned to think that bigger is better or because we're told by a real estate agent that a house has to be large to keep its value, we build the largest home possible. By stretching budgets to maximize square footage, we're then often forced to skimp on quality and performance. If, instead, we downsize the house, we can improve its quality (durability, detailing, energy efficiency, green features), and we might even be able to reduce the overall costs.

With green building, there may be some other ways to lower costs that don't require reducing the house size. At the development scale, if we design an onsite infiltration system for stormwater (rather than building a stormwater retention pond or installing storm sewers) that could both reduce costs and make the project greener. With larger facilities, it's sometimes possible to save millions of dollars with such changes -- paying for all of the additional green features.

Where we build can also influence cost. By clustering houses in a development, we can reduce the total amount of pavement, the length of utility lines, and other associated infrastructure costs. By putting a house fairly close to the access road, we both save costs and reduce the impacts of that additional pavement and material usage.

Relative to materials, there are some important ways to use materials more efficiently and save money. With "advanced framing," studs and rafters (or roof trusses) can be installed 24 inches on-center, rather than the standard 16 inches, reducing the amount of wood used in construction. By carefully planning overall building dimensions and ceiling heights, one can optimize material use and reduce cut-off waste.

And it's sometimes possible to have a structural material serve as a finished surface, obviating the need for an additional layer. This can be done when structural floor slabs are made into finished floors (often by pigmenting and/or polishing the concrete), or when a masonry block is used that has a decorative face, eliminating the need for another wall finish.

When it comes to energy, building a green, energy-efficient house usually does increase costs. But we can significantly reduce that extra cost -- occasionally even eliminate it -- by practicing "integrated energy design." If we spend more money on the building envelope (more insulation, tighter construction detailing, and better windows) so that we dramatically reduce the heating and cooling loads, we can often save money on the heating and cooling equipment. With a really tight, energy-efficient house, for example, we might be able to eliminate the $10,000 to $15,000 distributed heating system in favor of one or two simple, through-the-wall-vented, high-efficiency gas space heaters, or even a few strips of electric resistance heat.

If, along with that really well-insulated envelope, we carefully select east- and west-facing window glazings that block most of the solar gain and provide natural shading from appropriately planted trees, we might even be able to eliminate central air conditioning.

These savings on mechanical equipment can cover a lot of the added cost of the improved building envelope. In rare cases, these savings in heating and cooling equipment (if we eliminate a really expensive system, such as a ground-source heat pump, for example), we can pay for all of the envelope improvements and even reduce the total project cost.

I invite you to share your comments on this blog.

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The table at the beginning, by the way, is from an old Environmental Building News article that still has some interesting takeaways: Small is Beautiful: House Size, Resource Use, and the Environment.

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