Debra Rucker Coleman, Architect
Construction Costs
The energy saving potential of passive solar homes is explained on the Sun-Inspired Benefits page to range between 50% and 90%, but what about the costs? Is it really worth it to build a home that utilizes the sun which is passively transferred through south facing windows? Well, yes! But let's look further.
A version of Sun Plans Northern Sun won an award in the CT Zero Energy Challenge Website March 2012 for the:
Most Affordable Energy Efficient Project (cost/sq. ft.):
Connecticut homeowners Sam and Teri built their highly efficient home at a cost per square foot of just $101. Their labor of love resulted in an extremely affordable, energy efficient and environmentally friendly home. The home is a passive solar home with custom windows that allow heat into the home and minimize heat loss in the winter as well as a floor that collects heat from the sun throughout the day and releases the heat into the home when the ambient temperature drops. Other features include a geothermal heating and cooling system; efficient insulation, lighting, and appliances; and a PV system.
Passive solar as a low-cost green feature
Increasingly, mainstream media is beginning to point out that there is very little extra cost associated with adding passive solar when it is designed into a house plan from the beginning. Even though Les Christie, staff writer for, wrote "Green homes face a red light," he went on to discuss low cost alternatives. 'Because of the appraisal issues, developers often opt for installing only the lowest-cost green features. "Other professionals agree with Christie. "Some can be incorporated without much additional cost," said Curt Jones, a Connecticut-based civil engineer and green building consultant. As he describes the process for green certification, points are given for a wide variety of factors, some costing a lot, others costing nothing.
"Angling the home a little differently, for example, to catch more rays and help heat the house passively, may not cost the builder a dime."

Smaller is less expensive to build and operate

Choosing a smaller plan will yield the lowest construction and energy costs. Choose a plan with the smallest footprint with everything needed on a daily basis on the first floor. Then rethink if it is truly necessary to have all the spaces on the main level. While planning for aging has been a priority for many clients of Sun Plans, many do so with a healthy dose of practicality and most of the Sun Plans reflect that with their partially accessible design. Secondary spaces, such as children's bedrooms, hobby rooms, game rooms, etc., can then be placed either on a second floor, ideally nestled within the sloped roof area that may otherwise be left vacant, or in a sunny daylight basement. The footprint stays small, but the square footage increases. Sometimes a future elevator is planned in.

Simpler is less expensive to construct and to operate

Consider the home's complexity. The simplest home will yield the greatest square footage for the least cost. The Select-A-SunPlan List has a column for complexity. A very rough estimate is that a home that is rated "average" may be 10% more expensive to build than one rated "simple," and one rated "complex" may be around 20% more.

Concrete slab-on-grade foundations add thermal mass and are inexpensive

The combination of high thermal mass and low costs makes a concrete slab-on-grade foundation one of the best choices for all climates, not just southern ones. Building codes now address cold-climate slab foundations. A concrete slab over rigid insulation is the least expensive way to incorporate a lot of thermal mass and store the sun's heat that enters in winter. In summer, the earth below is typically cooler than the outside air, so the slab performs double duty of tempering the summer home temperatures too. Walking barefoot on a slab is delightful on a hot day! But what about cold days? Some like to add radiant heating in the slab for those inclined to go barefoot in winter, but another much less expensive solution is to wear slippers or comfy indoor shoes with cushions. Even hardwood floors, which people often choose saying that they are more forgiving, are designed very stiff today to avoid the squeaks and bounce of older floors, so concrete slab may not be very different at all. Concrete slab can be inexpensively finished with stains or elaborately covered with decorative tiles.

Interior and exterior finishes affect cost more than energy-related elements

Calculate all of the spaces, inside and out, that must be constructed, and not just the finished living areas. Calculate the cost-per-square-foot range from local builders to build each of the various types of spaces such as finished areas, porches, garages, deck and finished or unfinished. (Sun Plans often assists with this through Consulting Services.)

Although some builders may understandably be reluctant to provide exact numbers, they should be willing to provide a range in $/s.f. based on recently completed homes for other clients. Show them a Review Set with the construction details. Even though the Review Set will not have the Custom Energy Specs, a builder should still be able to estimate within 10% if they are also providing a list of finishes and fixtures anticipated, since those will have more effect on the final price than the energy details. Creating such a list can be applied to any home design, so it is worth spending time on it early in the planning process. Treating the builder as a consultant by possibly paying for the estimating services should result in the most accurate pricing.

Attention to insulation and sealing adds most of the costs

It's hard to isolate just the passive solar components since it is not recommended to add passive solar until a home's "envelope" - the surfaces (walls, roofs, floors) that surround the living spaces - is properly insulated and sealed. A good "container" is needed to hold the free energy. Holes in a bucket would be fixed before adding water. To create a good envelope, it takes a little extra time and typically a little more money from the home owner to install the insulation carefully and to caulk, seal and pay attention to air leaks. And as long as the insulated cavities are being sealed up "for good," if there is room without compressing it, why not put a little extra insulation in too?

Upgrade or add finishes later for tight budgets

Visible surfaces and products can be upgraded or replaced later if the initial budget is tight, but the wall, floor, rafter cavities and certainly below-grade floors may never have another opportunity for upgrades without a major renovation. Almost the only space that is easily upgraded with insulation is an open attic - usually those with a "truss framed" roof as mentioned under the Detail descriptions of Sun Plans designs.
Lower cost heating system
The additional energy required to heat the home can be greatly reduced with the combination of increased insulation, air sealing and a proper design of whatever type of supplementary or auxiliary system is used. Even the best-performing passive solar homes will still need some form of heating from electricity, gas or wood in addition to the sun, but much less of it. Heating systems can be downsized. For those engaging Sun Plans in Create-A-SunPlan or Adapt-A-SunPlan, an HVAC consulting service is available.
When in doubt, add more time! The cost of planning, which includes thorough research and pricing, should also be considered. Planning takes your time. Often, a higher cost can be associated with a lack of planning. Having Construction Prints at least two months prior to starting construction is a minimum. This allows for site work and engineering time. Six months would probably be more reasonable. Engineering analysis and review of your location and house plan may add changes due to such factors as high winds, snow loads, seismic activity or unstable soils. Building a home is a big investment. Spend your time and money wisely.
Passive solar homes typically result in energy savings from 40 to 75% over a minimum code-built home, when combined with above-code, energy-efficient construction. The additional construction costs associated with such standards as Energy Star for energy-efficient construction and passive solar design are typically 0 to 10%.
Why ask about cost-effectiveness at all? Isn't it okay to want a sunny home just because you want it? After all, is the cabinet maker asked if the large island is cost-effective? Or the bath fixture supplier asked if it is cost-effective to have both a shower and a large tub? If you want the sun coming into your home, simply request it. It adds no extra square footage unlike the features just described and will bring delight for days to come.
To read more about Construction Costs of passive solar features, see Chapter 3 of The Sun-Inspired House.
(Costs for active solar, such as panels for creating electricity and heating water, are an entirely different cost system and are not addressed here. Home owners will need to consult with a local solar installer if they intend to also include active systems.)