What if we thought of the homebuilding process as if we were building an airplane?
By: Steve Scheiner of Schreiner Design and NCBPA Board Member
Designing and building an airplane is a process of balances. You design an airframe that will be strong and aerodynamic to perform in flight, but this all has to happen inside the performance capabilities of the power plant or engines. Consideration must be given to the purpose of the airframe; passengers (comfort), or cargo (payload-carrying capacity). If the airframe is too big or heavy, or is not aerodynamic, the engines cannot get the aircraft airborne. One last design dynamic, fuel; fuel efficiency of the engines must be high to allow the airplane to stay airborne for a reasonable length of time. All of these design considerations must be in balance to produce an airplane with the needed and desired performance characteristics.
How can this design mindset be applied to homebuilding?
Consider that the house envelope is the airframe. The envelope needs to be designed to provide an effective indoor environment. The envelope sets the tone for everything that happens inside such as temperature, humidity, air quality, soundproofing, and protection from the elements. How well it is designed and built determines the size and performance of the HVAC equipment, which we will compare to the airplane engines. If the envelope is designed and constructed effectively it will greatly affect the need for HVAC, reducing its size. A smaller HVAC system needs less power, which we will compare to the power needed to keep the airplane in flight. Are you starting to see the correlation here?
A building program that puts it all together.
There is a building program named Passive House that utilizes the design and construction mindset outlined above. Passive House concentrates on building envelope-related items such as airtightness, insulation, thermal bridges, and windows before anything else. The envelope is designed to fit the specific climate location resulting in an economic and energy-efficient envelope system. This process greatly influences the peak loads of the HVAC system, potentially reducing heating loads 80% in heating climates, and reducing cooling loads 40% in cooling climates. I would say that is impressive and certainly justifies some consideration. You can only imagine what that does to energy use as well. “Yes Clark, it’s the gift that keeps on giving all year long.”
As in any construction design process, there are calculations, but do not panic; there are aids and they are called energy and optimization models. These models help to identify the most appropriate combination of materials and procedures in the envelope design process, and analyzes energy use of all other apparatus inside the building. Remember in the airplane design process, you cannot make the airframe too structurally sound, and thereby, too heavy to get off the ground. The same holds true with building envelope design. You do not want to add too much insulation for too little benefit, or it will be a “diminishing return”. This same process should be used before the consideration for renewables such as photovoltaic solar arrays, which I call “PV badges”. It is important to first minimize the energy use of the building and thereby reduce the amount of renewables needed to attain a zero-energy scenario. In other words, “reduce, before you produce”.
For more information:
Join me on June 25th from 2 – 3:30pm EST for a free virtual panel with three other industry experts that will be discussing how to incorporate Passive House principles and certifications into everyday residential and commercial projects. This is a free educational event hosted by North Carolina Building Performance Association (NCBPA), where I serve on the Board of Directors. Membership information is available online.
If you are interested in more information on Passive House, go to http://www.PHIUS.org. PHIUS (Passive House Institute US) is the national organization that manages this building standard.
You will also find on their website a list of CPHC’s (Certified Passive House Consultants) that you may want to incorporate into your next building design project.
Steve Schreiner, Schreiner Design
PLA, CPHC, LEED AP BD+C, Master CGP, NC Licensed General Contractor AB