What if I told you that it’s possible to build a house that uses up to 90% less energy than your current house? And combining that with solar panels you could heat, cool, and even charge an EV for just a few hundred dollars a year? Let’s take a closer look and explore Passive Houses.
Teslas and electric vehicles, solar and wind production, and energy storage like Powerwalls and Megapacks tend to get all of the attention when we talk about ways to combat climate change. But it’s going to take a wide array of solutions to make a real dent. And one of those that doesn’t get talked about enough is how we build our homes to make them as energy efficient as possible.
In 1996, the Passivhaus Institute in Darmstadt (darm-schtadt), Germany, set building standards to create low energy consumption houses that still provide comfort at an affordable price. This demanding, performance-based, energy efficient construction standard provides heating and cooling savings of up to 90% compared to conventional homes, and over 75% in relation to average new buildings. 1 That’s a pretty big gap, which raises the question: how?
Passive house buildings rely on five main principles.
1) A Highly Insulated Envelope
Quality insulation is fundamental to achieving the great performance of a Passive House design. Multiple layers of high-efficiency insulation materials are used to cover every surface from not just the roof and walls, but the slab and footing as well. The only exception is obviously the windows and doors. All of this is to minimize the heat exchange with the outside environment. Some examples of these layers are rigidur boards, oriented strand board (OSB), taped sheathing, air barrier tape, and plywood sheathing. Thankfully, several high-performance insulation materials are also environment-friendly, which increases the benefits, like sheeps wool and cellulose. 1 2 3 4
2) Thermal Bridge Free Heat likes to escape to where it’s colder. So the heat inside a building will always try to go outside if it’s cooler using the easiest path it can find. These are called thermal bridges, which are specific areas of the building envelope where the insulation is the lowest value compared to other areas, forming cold spots in the building. If these spots become too cold, they could lead to the formation of moisture and condensation, so Passive Houses are built with the concept of being thermal bridge free.2 5
A house’s studs can act as a thermal bridge. The same for a home’s footings or basement slab, so the continuous layer of insulation from the first principle is essential. But one way to make this easier is to also minimize corners, bumps-out, cantilevers, and dormers because they create geometric thermal bridges.2 It doesn’t mean you can’t have them, but they have to be accounted for.
3) An Optimized Orientation with High-performance Windows & Doors Bad orientation combined with low-performance windows and doors can cause significant heat gain or loss in a house depending on the time of year. In Passive House buildings, triple-pane windows and insulated frames are usually employed. Triple glazed windows are composed of three panels of glass separated by a spacer. The airtight gaps between the glass are filled with an inert gas, like argon, which is a poor conductor of heat transfer. 6 7
But even these high-performance windows and doors can be inefficient if they aren’t well-positioned. That’s why homes built using the Passive House standard are optimally designed and placed to harvest natural light and heat coming from the sun. They take the surrounding environment into consideration when designing the structure and placement on the land. One reason for that is a technique called passive solar heating, which allows homeowners to collect, absorb, and distribute solar energy right through their windows and doors. Passive solar heating has to be tightly managed to limit overheating in the summer and maximize heat gain in the winter.
For instance, to optimize heat gain, windows that feature a high Solar Heat Gain Coefficient are used on the southern side of the house, which means they let more solar heat through, which is ideal for the winter months. And in the summer months when the sun is higher in the sky, you have large roof overhangs to keep the sun out. Then on the east and west sides of the home, where the heat of the rising and setting summer sun can’t be blocked, you’d use low Solar Heat Gain Coefficient windows to keep the heat out.
You can also use materials inside the house like concrete floors to absorb the heat coming in through the windows during the day. At night they’ll slowly radiate some of that stored heat back out. Also, deciduous trees are beneficial for providing shade on the house in the summer months, but allowing the sun’s heat to pass through in the winter when the leaves are gone. 1 2
4) Airtight Envelope Passive house buildings are designed to minimize the number of holes in their envelope. All leaks around doors, windows, exterior electrical outlets, hose bibs, sill plates, and piping are properly sealed in order to not only stop heat loss, but also help to reduce moisture buildup or loss in cold weather. Reducing cold spots and places where condensation can happen not only provides comfort, but also improves the air quality by eliminating the risk of mold growth. 2 8
But an airtight envelope brings some problems, like … oh … say fresh air for breathing, which brings me to the last main principle.
5) Mechanical Ventilation You might think that with an airtight design that people aren’t allowed to open the doors and windows, but they can. It is allowed. But when you’re trying to maintain comfortable temperatures in a home when the outside temps aren’t ideal and in balance, that’s when you have to rely on mechanical ventilation systems like a Heat Recovery Ventilator (HRV) or Energy Recovery Ventilator (ERV). These silent, efficient devices can provide continuous, filtered, fresh air to the house, while pushing the stale air out. HRVs and ERVs transfer heat in order to achieve maximum efficiency and healthy inside air quality, but only ERVs transfer moisture as well as heat. This explains why ERVs are usually preferred in areas of high humidity and wide temperature ranges. 2 9
In winters, the system uses the warm, stale air exhausted from the inside to pre-heat the incoming fresh air. Humidity can be added to the incoming air, which is great in the winter time. I don’t know about you, but the older I get the drier I seem to be getting with each winter. I could really use an ERV right now. In summers, the system conditions incoming warm, humid air by passing it over coils or channels containing stale, cool air being exhausted from the house. Desiccants are used to take humidity away from the fresh air intake, which is good for the cooling effect. 9
Depending on the Passive House construction and the local climate, a dedicated heating and cooling system may not be necessary because of the internal gains from the sun, cooking, and people just living inside the house. To get a good idea how that might be possible, just take a look at the difference in heating energy required between a passive house and typical homes. A northern European Passive House needs just 15 kWh of heating energy per square meter of floor surface per year (15 kWh/m2a), a modern house would require 150 kWh (150 kWh/m2a), and a leaky house … which a lot of people live in … would need 300 kWh (300 kWh/m2a). Kind of a big difference. 2 10
Passive Houses can’t be compared to other certifications like LEED and BREEAM green building certification programs, which is something that I actually covered in a recent video. Passive House is just a performance-based energy efficiency design standard. The Passive House Institute accredits this certification, and within the Passive House standard, there are certifications for the house components, such as the building envelope, transparent components like doors and windows, and ventilation systems. Also, not all buildings can be refurbished to the Passive House Standard, so the EnerPhit certification is used for retrofits to verify the consistent employment of Passive House components. The targets for an EnerPHit House for the Space Heat Demand and the Space Cooling demand is <25 kWh per square meter (<25kWh/m2) per year. Not as a good as a purpose built passive house, but still dramatically better that a typical home.11 12
But is the cost to achieve all these benefits worth it? 13
According to the Passive House Institute US (PHIUS), a passive home costs about 5-10% more than a conventional house, but others estimate extra costs varying from 7-15%. Usually, as the size of the building increases the cost difference to a typical house decreases. 14
A study performed by the Passivehaus Trust, the UK Passive House Organization, analyzed the building costs of several Passive House buildings considering different construction methods and forms. The projects made in 2018 ranged from 1,296 £/m2 to 1,807 £/m2, and the major extra cost in the construction was related to wall and roof structures. However, the costs for each project can very depending on the size, complexity of the design, level of finishes and materials, the builder contracted to lead the project, and other factors that can affect the building cost. 15
Passipedia, which is a great resource for Passives Houses, shows a study of a conventional 149 m2 single family house compared to a standard house over 30 years. In 2010, the additional investment added up to €15,000 (8% extra), while in 2015 the total extra cost was reduced to €10,000 (5% extra). The calculated energy savings for heating over 30 years was €822/year, with annual additional cost of electricity for the ventilation system of €71. In the end, the homes cut €432 of annual cost burden. 16
As good as all of that is, there’s still improvements being made to techniques and components. Swisspacer, from Switzerland, for example, has introduced the Swisspacer warm edge spacer that uses one spacer bar for all three panes in a window, providing lower weight, less risk of gas losses, as well as long service life. 17
Another example is EcoCocons Straw Panels by the Slovakian company EcoCocon. This wall system is made of 98% natural materials, such as fiber layer and straw, and it can prevent heat-loss, excess humidity, avoid thermal bridges, provides healthy indoor air quality and building flexibility due to the custom-made dimensions. And when you think of straw and fire, you might be concerned … but because of their composition they can resist fire for 120 minutes! 18
Passive House buildings have several advantages such as comfort, money-savings, healthy indoor air, reduced energy bills, and long lasting quality. Since the first Passive House constructed in 1991, which is still running by the way, there are more than 25,000 certified Passive Houses as of January 2020. 19 Today, many countries and some states here in the US, provide grants and tax breaks for homeowners that install energy saving materials in their houses. There are also low interest rate loans available in many areas to cover high efficiency projects like these.20 While the focus on clean energy generation, like solar, wind, and energy storage, is where a lot of the focus should be for combating climate change, we shouldn’t forget about energy conservation. Things like Passives Houses can not only make a huge dent on our energy requirements, they can save us a lot of money in the long run, too. And you don’t have to do every single component of a passive home to make a difference. If you combine some passive house techniques with a solar panel installation on your home, it’s possible to achieve net-zero pretty easily, which is generating as much or more energy than you use. One family in Massachusetts did just that with an Oxford, Maine built modular home from BrightBuilt Home. Including heating, cooling, hot water, and charging a Chevy Volt, they pay a little over $400 a year for energy use.21
I don’t know about you, but I’d love to build a Passive House or Net Zero home.
- About Passive House – What is a Passive House? ↩︎
- Passive House: An In-Depth Guide ↩︎
- Passive House Design: Insulation–That’s a Wrap ↩︎
- A Case for Double-Stud Walls ↩︎
- What is a Thermal Bridge? ↩︎
- How Do Double And Triple Glazed Windows Work? ↩︎
- What is Triple Glazing and how does it work? ↩︎
- Passive House Principles ↩︎
- It’s Alive! Passive House Must Breathe. ↩︎
- A guide to Passive Houses: designs, costs and savings ↩︎
- Certification ↩︎
- GREEN BUILDING TRENDS: PROS & CONS OF PASSIVE HOUSE CONSTRUCTION ↩︎
- What is a Passive House? ↩︎
- Passive House FAQs ↩︎
- Passivhaus Construction Costs ↩︎
- Are Passive Houses cost-effective? ↩︎
- Warme Edge Swisspacer Triple ↩︎
- EcoCocon ↩︎
- General questions – Passive Houses ↩︎
- Passive Houses: 13 Reasons Why the Future Will Be Dominated by this New Pioneering Trend ↩︎
- Build with Rise – Treat House: A Net-Zero Modular Home In Massachusetts ↩︎