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
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 give you 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.