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 seasonal indoor range of about 25 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 extremely narrow range of indoor temperatures translates into very modest annual energy costs. Our own house uses less than $350 in electricity per year.
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?
Until recently, finished AAC walls have 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 (resulting from the Iraq war and the hurricane disasters), this cost differential between AAC and wood has closed.
The cost of all building materials is too unstable to provide more than relative figures such as these.
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 previously higher cost of AAC walls with the use of 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. Right now we can make a better house for LESS than conventional costs.
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, and they require poisonous termite treatments because of the proximity of wood to ground. 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 who have experience building AAC houses.
Can we contact you for technical help in building with AAC?
We are not representatives for the product and must refer all technical questions to the technical advisors employed by the various manufacturers. Sorry!
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.
- The site can be steep and more difficult and expensive to landscape because of the necessity of building terraces and outdoor steps .
- 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.)
- In the event of resale of the house, below grade space will be considered a basement, regardless of its designated use.
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 seems irrelevant when 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 is 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.
“The positive aspects of timber framed houses are vaulted ceilings with lots of high windows making the great room flooded with light and open space. Unfortunately the very elements that create this beautiful environment are a drawback to comfortable living. Open space is noisy and not private. Bright, open space is very useful for large public gatherings in churches and theatres but for people living together there is no place to go to be alone or quiet. Further the outside focus from the windows is to look up to the heavens but it is not easy to view the ground or see the garden.
With a ground level south-facing nearly-fully-glass front wall a few feet from the garden you step into an outside room that is visible from all rooms on the south side of the house. You can have all the light of a timber frame and all the glass but the focus is out and then up, not just primarily a view of the sky. This view of, and easy access to the garden, pond, trees and outdoors can be accessed from rooms with doors and walls and be either private or communal depending on the needs of the homeowner. You can create light and upward sky views with transoms over doors without forfeiting privacy and noise barriers.” – Virginia Hill