Passive or Net Zero Homes

I believe the most difficult thing for the average person to understand with regards to building a passive or net zero house is the fact that the house has to be treated as a single system. There are such tight tolerances with an extreme emphasis on craftsmanship to reach the energy performance side of building the home.  It truly takes a team to build this type of home and we have just such a team!

Twelve Steps to Affordable Zero Energy Home Construction

In conjunction with reading these 12 steps, please view our Quick-Step Zero Energy Building Techniques video and the 12 Essential Steps to Zero Energy video by Ted Clifton. Also please view our Zero Energy Home Case Studies.

1. Design for Zero Net

Zero Energy Home Massachusetts

  • Cost-effective zero net energy homes begin with the design. This is a very critical starting point!
  • The designer or architect should be familiar with all the steps involved in building a net zero home as outlined below, and should design the home so that these steps can be achieved in as cost-effective manner as possible.
  • The design should specify the following: the siting of the home to take advantage of the sun; the wall, floor and ceiling systems using advanced framing techniques; the insulation R-values for walls, ceiling, and floors; the airtightness standard for the building shell; measures to avoid thermal bridging; the window type, locations and u-values; the door type, locations and R-values; the hot water system and its efficiency rating; the ventilation and heating/cooling systems and their efficiency ratings; the southern roof over-hangs to maximize winter sun exposure and minimize heat from the summer sun; the appliances and their efficiency ratings; the roof size, pitch and orientation to get the most benefit from the solar panels installed; and all other measures that are needed for the home to become a net zero energy home in the most cost effective manner.

2. Use Energy Modeling for the Most Cost-Effective Zero Energy Home

  • The design should then be run through energy modeling software to ensure that the zero energy goal can be achieved with this design in a highly cost-effective manner. Based on the results of the energy modeling, the design may need to be modified to reach the net zero energy goal.
  • It is most effective to conduct energy modeling on different sets of energy-saving features during the design phase in order to determine the most cost effective mix of energy saving features that you are considering and to determine the smallest solar PV system necessary to achieve net zero energy for your design. For more information, please see Energy and Cost Modeling and the Energy Modeling Video.

3. Super-Seal the Building Envelope

Super seal the building envelope with spray foam and caulking for a tight building envelope.

  • Set an airtightness standard of 0.6 to 1.5 ACH at 50Pascals and create an airtight barrier around all six sides of the home. Depending on climate, a 2.0 ACH may be sufficient.
  • Use a Thermal By-Pass Checklist short form to identify areas that need sealing. The Green Building Advisor has excellent air sealing diagrams, available for free if you sign up for their 10-day free trial.
  • Ensure that exterior sheathing materials should does not have any gaps, and joints are mechanically tightened.
  • Seal the outer sheathing and the drywall ceiling before the inside drywall is installed. To learn more about exterior air sealing, see Airtight Wall and Roof Sheathing: Arguments in Favor of Exterior Air Sealing, and view the Exterior Air-Sealing video.
  • Use glue, caulking, spray foam, and/or products, such as Ecoseal or Siga Airsealing Tapes, depending on the size and location of the leaks. For more on sealing air leaks see Tape It? Seal It? Glue It? Sealing Weather Barrier Seams.
  • During the sealing process, check for air leaks with your hands and/or with a smoke stick while the blower door is running. Then seal the leaks and recheck. This is called Blower-Door-Directed Air Sealing. View the Blower Door Directed Air Sealing video.
  • Complete the air sealing along with the subcontractor and crew – be fanatical, systematic and persistent in finding and sealing every leak, checking your success with the blower door as you go.
  • After the sheet rock has been installed on the walls, seal the inner envelope while again checking with the blower door in order to identify and seal all remaining leaks while the blower door is running. View the Sealing the Interior Walls video.
  • Seal electrical boxes and plumbing penetrations after all electrical and plumbing work is complete. Consider using airtight electrical boxes on all exterior walls.
  • Minimize penetrations of the airtight envelop by:

4. Super-Insulate the Building Envelope

5. Minimize Thermal Bridging

  • Thermal Bridging can best be minimized in the design phase by a designer who includes cost-effective thermal-bridge-free details. View the Thermal Bridging video.
  • Use a Thermal Enclosure Checklist or Thermal Enclosure Checklist Guidebook to help you design and build with minimal thermal bridging.
  • Where thermal bridging cannot be avoided, closed cell spray foam or aerogels may help reduce it, but may not be cost-effective, compared to eliminating thermal bridging in the design phase.
  • Decks, porches and porch roofs should be designed and constructed to be separate from the house, so no thermal bridging occurs between the house and the porch or deck.

6. Use Highly Insulated Windows and Doors

  • Use insulated fiberglass doors with tight air seals.
  • Aim for a 14% window-to-floor area (WFA) for the whole house, with about 50% of the windows on the south side,insulated shadeswhere the common living areas should be located. Depending on local circumstances however, more windows on the south side may not always be cost effective. These are all things that should be decided in the design phase.
  • Use triple-pane windows with approximately 0.2 U-value, such as Harvey TributeThermotechAtrium NorthwestCascadeSolar ViewIntusMilgard or Alpen. Some double pane windows such as Milguard’s I-89 StyleLine, are achieving u-values close to 0.20 and should be considered.
  • Fixed windows and casement windows with multi-point locking hardware are more energy efficient than sliders and single or double hung windows, both of which have leakage issues.
  • Look for windows that have the smallest frame profile because the frame has a higher thermal transmission than triple pane glazing. It is more energy efficient to use fewer larger windows with the same glazing area as more numerous smaller windows, because larger windows have a higher glass to frame ratio.
  • Depending on energy modeling, current pricing and advances in technology, shop for the most cost-effective, energy efficient windows. Less expensive triple pane windows may be the most cost-effective in many applications. In some climates and applications, energy efficient double pain windows may be sufficient.

7. Use the Sun for Passive Solar Gain

  • Use Solar Tempering, which uses the principles of Passive Solar without the added cost of adding thermal mass to partially heat the house. View the Solar Tempering video.
  • Use higher Solar Heat Gain Co-efficient (SHGC) windows on the south side with a SHGC of about 0.4 or more, if cost-effective.
  • Have approximately 50% of the window area on the south side, or have the south side windows equal 6% of the window-to-floor-area (WFA).
  • Use optimal roof overhangs for maximizing winter sun and ensuring summer shade to the south windows.
  • Calculate the BTU gain from passive solar or from solar tempering during the design phase.
  • Consider installing insulated honey-comb shades, such as the Duet Architella shades from Hunter-Douglas, which may have an R-value of close to 4, in order to help keep out cold or heat depending on the season. They should be installed with minimal gaps at the edges or in tracks to be most effective; and the homeowner must be willing to close them on cold winter nights and on hot summer days.

8. Use the Sun for Electricity and Hot Water

  • Based on energy modeling, determine an optimally sized Solar Photovoltaic (PV) System sufficient to meet the energy  needs of the house after all other energy-saving measures have been taken into consideration. View the Solar PV video.
  • Get several quotes from reliable installers to get the most cost-effective system. Consider a leasing program, such as Sun Run, which can eliminate up-front costs; or consider financing your solar system through your local credit union.
  • Consider designing and building the home to be a “net zero ready” or “net zero capable”– a highly energy efficient home, sized and wired for future solar PV installation, which could become a zero energy home when the solar photovoltaic panels are installed.
  • Consider using solar PV panels to heat water instead of a solar thermal water heating system. As solar PV is becoming less expensive, it may be more cost-effective to add a few more solar PV panels to power an inexpensive, well-insulated standard water heater, instead of adding a solar hot water system. This can simplify zero energy home maintenance for the homeowner, and lowers costs for builders.
  • In warmer climates consider the cost-effectiveness of using a heat pump hot water heater, such as the G.E. GeoSpring Hybrid Watet Heater, the A.O. Smith Voltex Hybrid Electric, or the AirGenerate AirTap Hybrid in conjunction with solar PV. The AirTap can be vented so that the cold air exhausted from the system can be sent outside.

9. Create an Energy Efficient, Fresh Air Supply and Manage Humidityworking_of_erv

10. Use an Energy Efficient Heating and Cooling System

  • Consider an Air Source Ductless Heat Pump with Minisplits sized for the specific heating needs of the house and climate. Ductless Air Source Heat Pumps are one of the most efficient methods for home heating and cooling and are easy to install.
  • Highly energy efficient Air Source Ductless Heat Pumps include the Mitsubishi “Mr. Slim” Ductless Heat Pump. In cold climates, consider the “Hyper Heat” model that heats down to temperatures of -18 °F. View the Ductless Heat Pump video.

11. Install Energy Efficient Lighting

  • For lighting, use compact fluorescent light bulbs (CFLs) and light-emitting diodes (LEDs). Use LEDs in light fixturesLED Lighting Net Zero Energy homesthat get the most use, as they will last much longer than CFLs and are more energy efficient.
  • During the design phase, design window placement for optimal natural lighting and use smaller task lighting where possible

12. Select Energy Efficient Appliances and Electronics

  • For energy efficient appliances view Energy Star rated appliances on the Energy Star Products Page. For more simplicity, visit Top Ten USA for the 10 most energy efficient appliances in each category. View the Energy Efficient Appliances and Lighting video.
  • Consider installing manual on off switches or use power strips for all appliances and electronics (except the fridge) in order to reduce phantom loads, which even Energy Star appliances and energy efficient electronics have.

 

 When you are ready to take the plunge and construct one of these homes,  you will join with us in all of the craftsmanship and environmental stewardship that goes along with the quality and pride of designing and owning one of these very special homes!

 

 

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