Passive House Design(Last Updated On: January 10, 2019)
Passive House Design incorporates principles of efficiency to reduce energy needs for heating and cooling. The main focus is on insulation, air tight construction, high quality windows, energy recovery, and solar heat management. Passive House Design can be applied to anything from single family homes to large multifamily buildings.
Passive house design has five main principles:
- Continuous Insulation / High Quality Insulation
- Air Tight Construction
- High Performance Windows
- Energy Recovery
- Solar Heat and Solar Shading
Passive House Design
Heating and Cooling is the largest use of energy in homes and buildings. The main goal of Passive House Design is to increase efficiency and decrease the need for heating and cooling. There are 5 main principles used to accomplish this efficiency.
Continuous Insulation & High Quality Insulation
Passive house design and energy efficiency begin with insulation. You need to keep the warm air warm in the winter and the cool air cool in the summer. High quality insulation in new homes with a smart design is necessary to achieve this. Insulation is rated by R Value the higher the R Value the better the insulation is. There are 2 basic categories of insulation systems: cavity insulation and continuous insulation.
Cavity Insulation is the more traditional system for insulation and the less efficient of the two. When you put insulation in between wood studs or metal studs that is cavity insulation. It means the insulation is placed in voids, section by section. In cavity insulation there is not a continuous insulation wrap around the structure, it starts and stops. This means the framing, whether wood or metal, is not actually insulated and can transmit heat through the framing. This is called a thermal bridge. Thermal Bridging is bad for energy efficiency. It is especially a problem with metal framing. A thermal break is an intermediate material that stops thermal bridging. Thermal breaks are essential for Passive House Design.
The more efficient insulation system is Continuous Insulation. What continuous insulation means is that the entire structure has one continuous insulation layer that wraps around the entire structure without any materials interrupting or causing a thermal bridge. One example is EIFS, which stands for Exterior Insulation Finishing System. You can put the insulation on the outside of a house or building and then cover the insulation with a finish material like masonry, stucco, siding, or panels.
Continuous Insulation is by far the most efficient insulation system you can use. At our architecture firm we like to use a combination of both Continuous and Cavity Insulation whenever possible.
Air Tight Construction
Insulation is great for efficiency but if the walls and roof are leaking air then the insulation can not do its job. You need an air tight structure for insulation to maintain the desired air temperature. All buildings and homes have penetrations through the walls and roofs. There are drains, vents, windows, doors etc… At any location with a penetration or opening you need an air tight seal. There are many ways to achieve this including caulking and gaskets. We first try to minimize the number of penetrations to the essentials. You then want to make sure they are all properly sealed.
My favorite way to provide insulation and air sealing is to use closed cell insulation. Closed cell insulation is a spray insulation that expands and gets into all the cracks and crevices. It is an air tight and water proof insulation. This is a great way to provide high quality insulation and seal your walls or roof air tight.
Windows and doors also need to be tested by the manufacturers and all the product specification should show the air leakage rates. The lower the air leakage the better.
After the construction is complete you can test for air leakage by performing a blower door test. This is a test where a fan is put at an exterior door with an air tight plastic seal and blows air inside. The technician can then use an air pressure gauge to see how air tight the construction actually is. If necessary the penetrations can be re caulked or sealed to improve the quality of the seal.
High Performance Windows and Doors
Windows and doors should be of high performance. Insulated triple glazed windows are best. The window material also affects efficiency. The material choice will be a variable based on application, budget, and design aesthetics. There are low E coatings that can be applied to windows to make them more energy efficient. The insulation value of a window is rated by U Factor. The lower the U Factor the better.
If you build an air tight house or building you need to ventilate it. You may have exhaust fans in the bathrooms and kitchens but you can exhaust from other places as well. When you exhaust you are blowing the conditioned air outside loosing energy. Any new air you bring indoors will need to be heated or cooled and this uses energy. You can install an ERV Energy Recover Ventilation or HRV Heat Recovery Ventilation systems for efficiency. These machines use the temperature of the air to be exhausted to preheat or precool the air being brought in. Don’t worry the air doesn’t actually mix it just draws out the heat.
Solar Heat and Solar Shading
The oldest and most basic passive house design principle is solar heating and solar shading. You want the sun to provide heat in the winter and you want to block it in the summer. The two most common ways to do this is with trees and overhangs or sun shades.
Trees for Solar Heating Cooling
The sun can heat your home when the direct light passes through your windows. For Example if you are in New York the direct sunlight comes mostly from the south. If you have a lot of windows on the South Facade you will get free heat from the sun in the winter. The problem is you will also get heat in the summer. If you plant a Deciduous tree in front of the windows the leaves will block the sun in the summer. In the fall the leaves will fall off the tree and allow the sun to pass through until spring. This obviously wont work on a tall building but works great on small buildings and houses.
Overhangs and Sun Shade Devices
The sun is higher in the sky in the summer and lower in the sky in the winter. If you have an overhang or a sun shade it will block the angle of the sunlight in the summer when the sun is high in the sky. In the winter when the sun’s angle is lower the direct sunlight will pass right through the windows under the overhang or sun shades.
Passive House Design and Sustainable Design
There are many different techniques that can also be incorporated for sustainable design and energy efficiency. If you want to learn some more methods for sustainability we have a few other blog posts you can read. 21 Ideas for sustainable homes and 21 Ideas for Sustainable Building Design.
Thank You for reading our blog post on Passive House Design.
Please feel free to leave questions or comments below. We hope this was helpful. If you would like to discuss a specific project please contact us directly.
Author Jorge Fontan AIA
This post was written by Jorge Fontan, a Registered Architect and owner of Fontan Architecture.