Frequently Asked Questions

Is passive solar more expensive to build?

No. It can cost no more to build a passive solar house than a similar conventional structure. Considering its energy savings over time, a passive solar house is LESS expensive than a conventional house. Energy bills are commonly reduced by at least 75% for the life of the house, a veritable cash windfall for most people.

In North Carolina, our houses have a typical year-round indoor temperature range of less than 30 degrees, without operating mechanical heating or cooling systems. This means that unheated, our houses drop to about 55 degrees when outdoor temperatures go to zero; un-cooled, they climb to 78 degrees when outdoor temperatures reach 100 degrees. This narrow range of indoor temperatures translates into very modest annual energy costs. Our own house uses less than $400 in electricity per year and less than $800 in propane.

Passive solar design makes irrefutable economic sense. These economic facts are measurable – unlike the immeasurable pleasure of living in a house that is warm and sunny in winter and cool and shady in summer.

What does it cost to build with AAC?

Finished AAC walls cost more than conventional finished 2"x4" stud walls. One manufacturer gave us the following 2001 comparisons: $8/sq.ft. cost for conventional walls; $11/sq. ft. cost for AAC; $13 sq. ft. cost for brick (which is a veneer on conventional framing). We see from these figures that AAC has historically cost more than conventional wood framed walls, but less than brick veneer on conventional framing.

But with the steep increase in the cost of wood products, this cost differential between AAC and wood has narrowed.

The cost of all building materials is too unstable to provide more than relative comparative figures which are probably out of date now.

Our masons charge approximately the same amount to build with AAC as it costs per block to buy from the manufacturers; shipping costs vary with distance. More exact figures can be obtained with a call to the manufacturers, listed at the end of this section.

We have been able to offset the higher cost of AAC walls by using relatively less-expensive concrete poured-and-scored floors, and by designing uncomplicated roofs that can be built with engineered roof trusses. The combination of these three features allowed us to compete in cost with conventional construction while producing a vastly superior house. 

Can we build an AAC house that is not passive solar?

Sure! But we recommend against it. We had the opportunity to closely observe non-passive solar AAC houses built with crawl spaces and wooden floors: they are cold in winter and hot in summer, just like wooden houses. In most of the continental US, it is a mistake to build non-passive solar houses, regardless of their wall systems.

How do I find a contractor who will use AAC?

Contact the AAC suppliers nearest you for a list of contractors in your area who have experience building AAC houses.

Can we contact you for technical help in building with AAC or for help in other building and design questions?

We consult with owners, designers and builders around the country about a wide range of building issues.  Just give us a call.

Can I build over a basement?

Some clients may choose to build over basements; concrete basement floors can provide thermal mass for the house if they have a south face and the required glass. But, depending on the difficulty of excavation, walk-out basements with fully glazed south faces can sometimes cost only slightly less to build than houses, and this savings comes with trade-offs that must be carefully considered.

• The main first floor living space will not have direct south garden access; it cannot have a south-facing deck because a deck will shade the basementÍs thermal mass in winter. Accordingly, immediate first floor access to the outdoors must be designed for the east, west or north sides of the house. The south side of the house can have shallow balconies that shade the basement windows below.
• If most of the site is properly graded for garden orientation (i.e. one step up to entrances) there will be no windows to light and ventilate the other three below-grade sides in the basement. The placement of high basement windows will necessitate jacking the whole house out of the ground; garden orientation will be impaired by many steps to entrances on east, west and north sides.  These may be acceptable trade-offs.
• The main living space can utilize the solar mass of the basement if the two are connected for rising warm air. Otherwise, the main living space will also require a strategy for incorporating thermal mass in its walls or floor – or be designed as solar tempered rather than passive solar. (Solar tempered spaces have south windows but do not have adequate thermal mass; to avoid wild temperature swings, south glazing must be smaller than in a passive solar space.)
• How do houses built with SIPs wall systems compare with your AAC/passive solar houses? How about post and beam timber frame houses?

SIPs (Structural Insulated Panels) are made from polystyrene and OSB (Oriented Strand Board), which are not environmentally friendly materials – and they have all the fire and insect problems of conventional wood houses. SIPs walls have a higher insulation value than AAC, but this is irrelevant given the high performance of our houses and all the environmental tradeoffs.

SIPs houses can be conventional or they can be passive solar. SIPs can be incorporated in post and beam construction.

SIPs are more expensive than AAC wall systems; and post and beam is astronomically more expensive. In the account below, Virginia Hill compares her post and beam house that used SIPs with our AAC passive solar houses. She has the unusual advantage of having acted as her own contractor in building both a conventional post and beam timber frame house and one of our passive solar AAC SunGarden Houses.