Zero Net Energy Homes | Retrofit & Conversion

Frequently Asked Questions

Our FAQ provides responses to a variety of often-heard questions about Passive House, sustainable building practices, climate change and electrification. If you have questions of your own, feel free to send an email to info@carmelbuilding.com.

Passive House

Passive House (called Passivhaus in Europe) is an advanced building concept and set of standards. It results in homes (and other buildings) that not only require 75% to 90% less energy for heating and cooling, but are also more comfortable, quiet and durable, and have healthier indoor air quality and a lower carbon footprint than conventionally built homes. The home’s remaining energy needs can typically be met with onsite solar panels. For more information on Passive House design/build principles and benefits, explore our Passive House page.

Can I opt for a Passive House without certification?

Many Passive House principles, based on building science, are incorporated into every home we build and remodel. We walk through each client’s goals and present options for sustainability and energy performance, whether it’s going all electric and pursuing a true Passive House, with or without certification, or simply improving the performance of the home and lowering its carbon footprint. It is possible to choose Passive House without certification, but the certification process ensures that the home will perform to the rigorous Passive House energy use standards. A recent study of home sales in California revealed that homes certified as energy efficient sell for a 9% premium today, and it’s anticipated to increase.

What are the criteria for a home to be certified as a Passive House?

There’s an energy budget that the house is allowed to use for heating and cooling. This is called “demand.” The living space must use no more than 15 kilowatt-hours per square meter per year (15 kWh/m²yr) for that purpose.

Another component to the heating and cooling energy budget accounts for making the space comfortable on the hottest and coldest days of the year. This is called peak load. The maximum energy use allowed for heating and cooling under peak conditions is 10 watts per square meter (10 W/m²).

There is also a total energy budget for running everything in the house that requires power or fuel. This energy can come from different sources (gas or electric, renewable or non-renewable, near or far). Passive House design considers all of these variables and calculates the Renewable Primary Energy (PER) demand of the home. For example, a gas appliance will increase the calculated PER because its energy source is non-renewable. PER for a Passive House “Classic” cannot exceed 60 kilowatt-hours per square meter per year (60 kWh/m²yr). Maximum PER is even less for Passive House “Plus” and “Premium.”

In order to create an energy-efficient home, it is crucial to minimize air leakage. Passive Houses are built to rigorous air tightness standards. The air tightness of a Passive House (measured in air changes per hour) should be at or below 0.6 at a standardized air pressure.

A consistent, comfortable indoor temperature is one of the primary goals of Passive House design. The living space of a Passive House should be at or below 25°C for at least 90% of the hours in a given year.

I want to lower the carbon footprint of my home. How does Passive House achieve that?

A Passive House requires 75% to 90% less energy for heating and cooling than a conventionally-built home. And when high-efficiency, all-electric mechanical systems and appliances are used, the energy demand is even lower. The low energy demands of a Passive House can be offset by renewable energy sources like onsite solar panels. As decarbonization of our energy infrastructure progresses, all-electric systems will realize even greater carbon-reducing capabilities. Learn more about Passive House here.

What are the primary benefits of living in a home built to Passive House standards?

There are myriad benefits to living in a home built to Passive House standards. Compared to conventionally-built homes, they are quieter and require significantly less energy to operate. They provide a more consistent, comfortable indoor air temperature, and can better maintain it during a power outage or extreme outdoor temperature fluctuations. The continuous supply of fresh filtered air creates a healthy indoor environment with fewer allergens and toxins. The well-sealed and -insulated structure protects against water intrusion, preventing mold and rot and decreasing maintenance costs. And, it’s easier on the planet.

Does it cost more to build to Passive House standards?

Building to Passive House standards can be done at little or no additional expense, and results in a home that costs less to operate and maintain.

Can I have (or do I need) heating and air conditioning if I choose a Passive House?

A Passive House is designed for maximum energy efficiency by controlling heat gain and loss in the home. Depending on where you live, you will probably need a small-scale heater or air conditioner such as a mini-split heat pump (and one may be required by building or tenant codes). A properly-sized system, which is much smaller than a conventional system, will cost less to buy as well as lower your energy bills.

How does a Passive House maintain healthy indoor air?

In a standard home—which is not typically air tight—pollutants and moisture from wall cavities and crawl spaces can creep in through gaps and penetrations. A Passive House controls these intrusions through air sealing and proper insulation. A Passive House is also designed to provide its occupants with regular fresh air exchanges through a heat recovery ventilator (HRV). The intake for the HRV is located away from pollutant sources. The air is filtered, drawn into the “dry” rooms of the house, and exhausted out of the “wet” rooms (bathrooms, kitchen and laundry). This design minimizes moisture, allergens and pollutants in the conditioned space.

Are Passive House buildings fire safe?

A home’s ability to survive a fire partially depends on the types of finish materials used. It also depends on the integrity of the building envelope. Many houses that catch fire do so because fire or embers enter the house through attic vents or other holes in the structure. When less-combustible materials are used, and the structure has fewer intrusion points, it is safer from the threat of fire. A metal roof and stucco siding are examples of good material choices. An external insulation system that is fire resistant, such as Rockwool or Gutex fiber board, can also aid a building’s ability to endure a fire. An air-sealed home equipped with a heat recovery ventilator has been shown to protect against smoke intrusion. Window glass is one of the more fire-vulnerable components of a home’s exterior. There is evidence that multi-paned glass and low-e coatings can increase a home’s fireproof qualities. For more information, see this article about one of our Passive House projects.

Sustainable Building

Sustainable building is an overarching approach employed to encourage responsible use of natural resources, reduce energy demands and lower negative impacts on the environment. It encompasses everything from reducing the building’s energy demand and related carbon emissions to using reclaimed materials or those that can be more easily replenished like bamboo and Forestry Stewardship Council certified lumber, choosing renewable energy like solar and wind, and avoiding products that contain volatile organic compounds (VOCs). Building approaches such as Passive House, LEED, Zero Net Energy and others provide a pathway to building high quality, healthy human habitats while sustaining and replenishing the earth’s resources. Learn more here.

What does it mean to air seal a home?

Air sealing is the process of creating a continuous, airtight building envelope to eliminate uncontrolled air movement in and out of the house. This includes identifying all of the external building components, joining those together with airtight material, and sealing all penetrations from inside to outside at conduits, pipes, outlets and penetrating fasteners. For more information, see our air sealing video.

If my home is air sealed, can I still open doors and windows?

Yes. The powerful air filters included in the heat recovery ventilator continue to filter out dust, allergens and other particulates and pollutants even when doors and windows are open.

Mechanical Systems and Appliances

The overriding goal is to replace mechanical systems and appliances that involve combustion and related harmful emissions with those powered by electricity. Innovations in the technologies that support electric options and the growing availability of electricity provided by clean, renewable sources make switching to all-electric a viable alternative. As more of us move to all-electric options, we should see a reduction in the cost of the systems and appliances, as well as the associated carbon emissions and their contribution to unhealthy indoor air and global warming.

What is Heat Recovery Ventilation (HRV)? What are the benefits?

An HRV system continuously extracts moist, stale air from wet rooms such as kitchens, bathrooms and laundry rooms and replaces it with fresh, filtered air throughout the living spaces. Up to 90% of the heat in outgoing air is recovered by the heat exchanger and used to heat the incoming fresh air. This saves money and energy and keeps the house more comfortable.

The high-efficiency HRV filters keep outdoor pollutants (mold, pollen, dust) from getting indoors. Frequent air exchange prevents indoor nuisances and pollutants from accumulating: moisture (that causes mold); cooking odors; volatile organic compounds from off-gassing materials, hobbies and cleaning products; soot and gases from combustion appliances, fireplaces and smoking; and carbon dioxide buildup from inhabitants and combustion. Indoor air pollution is especially concerning for people with chronic diseases, compromised immune systems, or mold or chemical sensitivity. To learn more, see our HRV video.

What is Heat Pump Technology?

Heat pumps draw heat from outside and pump it inside using systems that include refrigerants and compressors. The system can also be reversed to pump heat away from a space, cooling the space down in the same way as a conventional air conditioning unit. Because a heat pump uses electricity and refrigerants to transfer heat rather than burning fuel to generate it, a heat pump is substantially more energy efficient than a traditional HVAC system. Heat pumps are also used to heat water and power clothes dryers.

Are there good alternatives to gas appliances?

Yes! Gas appliances like stoves and water heaters can release toxic pollutants and greenhouse gases into the environment, and your home. Heat pump water heaters, heat pump dryers, HVAC heat pumps and electric induction cooktops are highly energy efficient and do not involve burning fossil fuels. As our electricity sources continue to move away from fossil fuels and toward renewable sources and battery storage, the benefits of home electrification will continue to increase.

Electrification and Climate Change

Electrification, one aspect of decarbonization, is the shift to using only electricity for energy rather than relying on fossil fuels. Decarbonization is the process of society reaching net zero greenhouse gas emissions by shifting to renewable energy generation, removing combustion from the home, improving energy efficiency to decrease demand, and enhancing carbon dioxide removal from the atmosphere. These concepts are fundamental to curtailing the heating of our planet.

Why is it important to reduce the amount of energy needed to operate my home?

When we reduce the amount of energy required to power our homes, not only do we reduce our energy costs, we also reduce the negative impact of fossil fuel extraction and greenhouse gas emissions on the environment. Homes that are built to the rigorous energy usage standards of Passive House, that also incorporate electrification and onsite solar, go a long way toward achieving significant reductions in energy use.

What does zero net energy (ZNE) in a home mean?

Simply put, it means that the amount of energy generated by onsite renewable sources like solar is equal to the amount of energy used to operate the home. ZNE is easier and more cost-effective to achieve by first reducing demand, which can be achieved through Passive House design to maximize efficiency.

What is embodied carbon vs operational carbon?

The embodied carbon (EC) of an object refers to the net greenhouse gas emissions arising from all aspects of making it, including extracting raw materials, research, design, fabrication, manufacture, transport, use/operation, maintenance and disposal. The operational carbon (OC) of an object refers to the greenhouse gas emissions produced by operating the object. EC and OC are typically discussed in the context of the built environment, but can apply to anything.

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