Debra Rucker Coleman, Architect
Construction Costs
The energy-saving potential of passive solar homes is explained on the Sun-Inspired Benefits page and is typically between 50% and 90%, but what about the construction 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.
FAQ-Can you tell me how much a particular house costs to build?
  • Sharing construction costs from one client and location to another could hurt more than help. There are many factors to consider such as date of construction, location, climate, client energy priorities, interior finishes, etc. With custom services where Sun Plans reviews your wish list and priorities in detail, and with Review Set orders, we can provide an opinion of construction cost. As a rule, a sun-inspired home should cost the same as any other same-sized CUSTOM home in your area that is built to Energy Star standards at least. That comparison will be the most accurate one short of getting a local builder to price the home from the Review Set. The Review Set cost is deductible from orders of Construction Prints and CAD Files even if you switch to another Sun Plans design.
FAQ-Do I need to have a builder who is experienced in passive solar?
  • No. The information below and elsewhere on the website explains that the primary elements of orientation, a well-insulated and sealed home, window placement, and sometimes extra thermal mass like a slab or grade or interior stone on the walls for some homes with south glass that equals more than 7% of the heated floor area, are straightforward items that mainly take skills of following the plans and custom energy specs.  Awareness of the importance of these items and others such as overhang length is also beneficial. Because "passive solar" is sometimes an understandingly misunderstood term with wide meaning (it is not the same as building to Passive House standards although that is still possible), it is often better not to mention passive solar during selecting a builder or certainly not disqualifying an otherwise good builder that is open-minded and willing to listen to anything different a homeowner may bring up.
Finishes chosen can have more of an implication than energy-related features. A wide difference in costs is based on personal tastes in both interior and exterior finishes which can affect the construction costs more than the energy-related elements.
An Example of Affordability
Although it has been a while, the premise holds true. 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.
Those were 2012 costs. While the same home would be comparably affordable to build, today's construction costs are much higher for any custom home. The home is also a compact two-story design with a small footprint. Larger one-story homes typically cost more per square foot due to a large footprint. A premium is paid for building any custom home. Building a sun-inspired home has special features like any other custom home, but a sun-inspired home may have more windows, better insulation, a more efficient (but also smaller) heating and cooling system, and other energy-saving features as well as a right-sized floor plan with less square footage.  A non-Sun Plans custom home may have higher-end appliances, fancier fixtures, and often wasted floor plan space certainly when compared to a custom design by Sun Plans.  A good starting point for figuring construction costs is to look at other custom homes being built nearby as opposed to spec homes that are often built more in subdivisions where the builder constructs more than one home at a time. Ideally, compare to a home that has been built to the Energy Star standard which is about 30% better than code since that is the minimum energy efficiency that is recommended by Sun Plans although most clients choose the 50-90% level of savings.
Passive solar as a low-cost green feature
Even mainstream media has pointed out that there is very little extra cost associated with adding passive solar when it is designed into a house plan from the beginning.
"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."  - Les Christie, staff writer for
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.
Simpler is less expensive to construct and 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" maybe 10% more expensive to build than one rated "simple," and one rated "complex" maybe around 20% more.
Concrete slab-on-grade foundations add thermal mass and are inexpensive
The combination of high thermal mass and low costs make 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 the 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 that is often overkill in all but the coldest of climates so 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 slabs may not be very different at all. A 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, decks, and below-grade or daylight basements. (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 need not add 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. Creating a good envelope takes a little extra time and typically a little more money from the homeowner to install the insulation carefully and to caulk, seal and pay attention to air leaks. If a builder builds tight homes routinely (and does blower door testing to prove it), then it would not be an extra cost. Fortunately, most building codes require blower door testing although not all enforce it.
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/right-sized design of whatever type of supplementary or auxiliary HVAC 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 small to moderately-sized sun-inspired homes, the most common heating (and cooling) systems are the small, mini-split heat pumps - even for cold climates. Radiant heating and geothermal heat pumps are seldom cost-effective as are larger, more complex heating and cooling systems. Smaller and simpler is a good strategy for the HVAC system just like the overall house design.
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 significant 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. (Of course, they can be even higher with the higher levels of insulation, and some Sun Plans homes are nearing 100% passively heated and cooled.) The additional construction costs associated with various standards such as these programs including 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 years to come.
To read more about the Construction Costs of passive solar features in general, 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. Homeowners will need to consult with a local solar installer if they intend to also include active systems.)