Karl and Perry Ludwig purchased this small Kachina Village lot in 2013. To optimize the building envelope on the site, the initial design was for a two story home. The aesthetics of the two story weren't appealing so they switched to this low-slung design that blends better with the environment.

This home is passive solar, designed to get most of its heat in winter from the sun through the south windows. It is oriented for maximum solar gain, with its length along the East-West axis. The sun also provides light, making this a beautiful bright space.

Passive solar design applies understanding of sun angles during different times of the year to bring sunlight in during the winter months when its needed, and exclude it during the summer months when the sun is overhead.

Another key component of passive solar design is thermal mass. The concrete floors of the house absorb the heat from the sun during the day and then release it at night. Another sustainability advantage of this type of floor, is that requires less material than typical floors which use the concrete as a base layer for other flooring options.

Fall and spring can be tricky times for passive solar design as the temperatures are so variable. The Ludwigs added these Coolaroo shades that give them flexibility in letting sun in when needed and blocking when it isn't. The shades also add a nice design element and better define the patio space.

As the saying goes, "even the best windows are a hole in the wall". Windows on the north wall were minimized as they do not receive sun during the winter and are a source of heat loss.

The window package was optimized for passive solar. The windows on the south have a relatively high Solar Heat Gain Coefficient (SHGC) of 0.5, while those elsewhere are lower (0.27). Window coatings can add to the insulative value, lowering the U-value, but tend to block sunlight also lowering the SHGC. It is a bit of a trade-off and the window manufacturer can help with optimization.

Structural Insulated Panels make up the walls and ceiling of this home. SIPs are a sandwich of expanded polystyrene insulation between two sheets of OSB (oriented strand board). These panels were manufactured by Enercept, and the OSB sheets are made from sustainably sourced materials.

All the joints between panels were sealed with flashing tape, making for a very air tight building envelope. Air leaking into a building must be heated to maintain a comfortable temperature, increasing energy usage.

This home is a small, one-bedroom home- only 960 square feet. The owners say they use every part of the house every day and don't feel cramped at all. Small houses are a great strategy for reducing carbon footprint because of the energy use and associated carbon outputs of material manufacture as well as operational energy. The less materials used, the lower the carbon footprint, with the exception of carbon sequestering materials.

The home is heated with in-floor radiant heat. The slab is insulated with rigid insulation to prevent heat loss to the earth.

The radiant heat system is supplied with hot water from an on-demand Energy Star combination boiler that provides for domestic hot water as well. With the passive solar design, high-efficiency mechanical systems and air-tight, well-insulated building envelope, the combined gas and electric bill for this house is only $50 a month!

With a building as tight as this one, it is a good idea to consider ventilation. This home has an Energy Recovery Ventilator that captures heat from outgoing stale air and shifts it to the air coming in from the outside through a heat exchanger. This is the most energy-efficient way to ventilate a home.

Due to the home's small size, a smaller duct system is needed. This one is exposed as a design element.

Ceiling fans are an energy efficient way to move air and cool the home. There is no other cooling system in the home. The home is designed to have passive cooling through cross ventilation from windows on opposite ends of the home.

Water savings means energy savings as well, as it takes energy to gather, treat and distribute water. This home has low flow fixtures, including this dual flush toilet. Dual flush toilets typically use half the water of a standard flush toilet for the low volume flush and the standard 1.6 gallons for the high volume.

While the ERV will be keeping the home well-ventilated, low VOC (volatile organic compound) paint also will ensure the indoor air quality is healthy.