A net zero house is one that produces as much energy as it consumes. That idea resonated with our clients so we designed a super tight, highly insulated, compact home and offset its meager energy demands with a rooftop solar array and a ground source geothermal heat pump system. The result is a very sustainable home that, we think, is truly easy on the eyes.We first walked the site with our clients in the winter when the prairie grasses, woods, and pond were in full view. It’s a gently sloping site with a slight rise off the road followed by a gradual descent to a lovely little pond to the north. All agreed that the house wanted to sit in the prairie, just past the rise, focusing on the pond.
The preliminary design process consisted of a series of plan diagrams and axonometric massing models, beginning with a one-story approach stretching east to west across the site that gradually morphed into a more compact and energy efficient two-story form that sat more lightly on the land. Once the basic two-story approach was solidified the idea of a second story for sleeping sitting atop a one-story podium for living gradually evolved. After a number of combinations, we all agreed that a simple white cement board box with cedar accents floating above a continuous black, corrugated metal base of house, garage, and screened porches was the most elegant way to go.
The three-story section through the two-story living/dining area and its bridge illustrates the relative simplicity of the of the envelope and its insulation. There are 4” of rigid insulation board under the basement slab (R-16), 14” of Insulated Concrete Forms for the basement walls (R-22), a combination of 5 ½” of cavity batt insulation and 2 ½” of rigid foam sheathing for the above grade wall framing (R-32), and a combination of approximately 4.5” average of rigid polyisocyanurate and 6” of closed cell spray foam for the flat roof insulation (R-62).
A tight envelope is every bit as important as the amount of insulation, so contractor diligence is the key to a high performing home as are triple pane windows, energy efficient appliances, and LED lighting. After the home is virtually finished it’s time to bring in an energy rater to test the envelope.
The energy rater tests everything from exhaust fan performance to the required distribution of air through the sealed ductwork to each individual room in the house. Then he/she closes all of the windows, doors, and any other exterior penetrations to properly test the tightness of the envelope itself. This is done by replacing the front door with a red plastic membrane containing a fan which sucks air out of the house. The rate at which this air is withdrawn from a house at a specific pressure measures the tightness of the envelope. This house measured .68 Air Changes per Hour @ 50 Pascals, much lower than 1.0 ACH that is the typical target for high-performance new construction.
We’ve focused this blog on the net zero performance of the house, but I’d like to get back to the “easy on the eyes” thing. Hopefully you’ll feel as I do that high performance need not sacrifice elegant design, fine detailing, and skilled craftsmanship!
SALA Architects is pleased to be showcasing this home on the 2023 Homes By Architects Tour this Saturday, September 23rd and Sunday the 24th from 10:00 am to 5:00 pm!