I think it’s time for me to introduce my readers to one of the most important concepts of building eco friendly homes. House as a System.What do I mean when I say your house is a system? It is a combination of inter-dependent parts that make up a whole building. As an energy professional and an architect, that means, if I chose to change one part, I am affecting other parts of the system. This may be in a good way, or it may be in a harmful way. With the emergence of building tight homes, we also need to be aware of what we are trapping inside that previously exited though drafty or leaky areas in the home. I was going to write “older homes”, but my experience as an energy auditor has taught me that it has little to do with the age of the home. There are just as many leaky, drafty, inefficient new homes as there are older homes.It is extremely important today to understand the impacts of building more efficient homes. This rule applies to architects, builders, and energy professionals. The chemicals found in our building materials can be very harmful to your health. Many products are made with formaldehyde or high volatile organic compounds (VOC’s). Maine also has high levels of radon due to the rocky ledge that makes up our soils. By building tighter homes, we must be sure we are not trapping harmful gases or compounds within the home.Building tighter homes isn’t just about air sealing with caulks and spray foams. Adding dense packed cellulose to your walls increases the insulation value of your home, but it also reduces the air infiltration. When we reduce the air infiltration we can cause our atmospherically drafting heating appliance to blow exhaust fumes back into the home instead of out through the chimney. We can trap moisture within the home, propagating mold growth and moisture damage. Many building professionals believe that houses needed to breath and that is simply untrue. Houses do not need to breath, the occupants do. And we need to be sure that the air our homeowners are breathing is both healthy and adequate.Houses that breathe draw in outdoor air from anywhere there is a hole or crack in the building structure. This often times means that air is coming in from your basement. When you think about the principle that hot air rises, you can imagine the cool air being drawn in from your basement and leaking the heated air out through your attic. Now if you think about your basement, you may be thinking about a dirt floor, all the chemicals you store there, or your heating system. All that air that is being drawn in through your basement is introducing those chemicals into your living space. We have a tendency to think of our basements as outside of our living space, but they are very much connected to every other part of your home. Although the things you store there may be out of sight, out of mind, they are definitely not out of the air you breath.Before the emergence of energy efficient and airtight building, homes were able to dry out due to the air movement through the structure and the lack of insulation in the walls. The homes would dry during the wet seasons of the spring and fall, however, these same homes would become very difficult and expensive to heat during the winter. The energy community knew they needed to button up the homes, but at the time, they did not know that they needed to provide mechanical ventilation for healthy indoor air quality and they created several sick buildings.Now we talk about passive house building where there are less then 15 quarter-size gaps, cracks, or holes in a building structure and the sun heats the home virtually eliminating the need for a heating system. These inter-dependent parts create a very efficient design. In passive house standards, it extremely important to provide mechanical ventilation to the space. Providing fresh outdoor air to the occupants of the home eliminates harmful byproducts from the construction materials and excess moisture from cooking, breathing, and showering. Because the home itself has very little air infiltration, mechanical ventilation is often provided by a heat recovery ventilator or energy recovery ventilator. This allows the system to provide fresh air directly to the locations of the home that need it, like the bedroom, where you spend most of your time while you are at home. Providing air directly to the locations where it is needed instead of drawing it in from wherever there are cracks in the foundation allows for the system to perform with precise calculations and reduces any loss associated with providing healthy indoor air quality.The increased levels of insulation from the code minimum help to keep heat within the building envelope. Large south-facing windows can take advantage of the sun and heat the home through heating thermal mass, often a concrete floor. All parts of that system have to work precisely together to make the house as efficient as possible. If a new homeowner came in and decided to throw a carpet over the concrete floor they would reverse the effects of the solar heating system and require a larger heating system to be installed. Tighter homes often do not have large gas cook stoves with 300 to 600 CFM ventilation hoods because there is simply not enough air infiltration to provide adequate supply to the ventilation system. Without that adequate air it causes the ventilation system to “suck” on the house and will quickly burn out the motor in the fan.These are just a few examples of how the components of your home work as a system. So as you are building your home and thinking about making something that is more efficient, make sure you consider hiring a professional who can provide you with the information you need to save money, but also provide you with a safe and comfortable home. It may sound daunting to build an energy efficient home, but the comfort level it can provide you and the energy it can save you is well worth the added considerations during the design or renovation process.