How do I pursue an energy efficient build for my home?

By Tracee

“Energy efficiency” can be a fairly abstract term when it comes time to prioritizing and taking action. For our EarthFest open house and booth at the Expo, we wanted to help people understand and move to action on energy efficiency as easily as possible. We are also very empathetic to consumers regarding the lagging knowledge and practice of energy efficient construction techniques and strategies among building professionals; building to code still dominates the market.

So, we had our friends at XRG Concepts (Brandon Vagt and Megan Gallagher) along with our energy efficient evangelist friends Ivan and Mary Idso help us develop the following questions that YOU can use to vet building professionals and make sure you get what you want.

If your building professionals can listen to your desires, and answer the following questions, you can feel confident that you will not only have a good working relationship but are aiming at the same goal!

1. I want maximum energy efficiency in my home. What techniques have you used to create maximum energy efficiency?  

You should hear multiple strategies from among well-known building-science principles. We employed all of these strategies in our home:

• Super insulation:
  • Achieve energy efficiency with R30 (or greater) walls and R60 (or greater) roof. Code requirement of R21 walls represents a minimum health and safety standard, not a high-performance standard.
  • Continuous insulation: minimize gaps; use raised heel truss roof to increase depth of attic insulation and maximize coverage,
  • Minimize thermal bridging: external/internal insulation or double stud wall.
• High-performance windows (see also question 2)
• Weather-tight enclosure (see also question 3)
• Use some form of heat recovery ventilation (see also question 3)
• Properly sized space conditioning system (see also question 4)

Additional design techniques we pursued in our home to capitalize on passive energy:

• South-orientation for windows to reduce heating needs
• Thermal mass to store heat from the sun in the winter and decrease temperature swings year round
• Overhangs to block summer sun
• Simple overall shape of the house

2. I want high performance windows to take advantage of passive solar gain, yet still shield from undesired heat/cold gains. What kinds of energy efficient windows have you installed and what are the optimal placements and sizes?

Contractors may push double pane windows because this is what they are used to (and have ready access to), but triple pane windows are essential for energy efficiency: they provide a superior thermal boundary and prevent convection currents along glass surfaces. The frame assemblage is as much of a consideration in its performance as the number of panes. We looked for 3-paned windows that were third-party tested and rated high for our region. Our builder’s original bid included a high-end double pane window, but not rated to perform at passive house standards. We independently requested bids from four companies and chose WASCO windows, which met passive house standards at a similar price to the high-end double pane windows.

To determine window placement and size, we used Passive Solar rules of thumb, including the suggestion that 8-12% of the wall area be windows, with 80% of these windows facing south. Anything less than that and we squander opportunity for solar gain; anything more than that and the lower R-value of the window will make it less practical.

3. I want my home to be weather-tight for comfort, health and energy savings. Where are the areas of greatest air infiltration, and what techniques do you use to minimize leaks? How will I know my home is weather-tight?

You may get advice from well-intentioned folks that a house needs to breathe, so don’t build tight. However, building leakiness into a home is not practical for energy efficiency. As XRG Concepts reminds us, “Tighter is always better, but also a tighter home requires a stronger focus on ventilation.” Your building professional should name areas of a home where there are breaks in the continuity of the structure, such as sill plate/foundation connection, and window/doors in their rough openings. These are called “Material Transitions” in construction lingo, and it pays to have your construction professional name the materials and construction techniques they use at these points.

To ensure your home is being built weather-tight:

• Before construction: consider having your contractor/architect do a “pen test”
• During construction: review Material Transitions on site
• During/after construction: Have a blower-door test conducted. This test measures the difference in pressure from the outside to the inside, which tells how much air is moving through the building envelope. The lower the test result, the tighter the building envelope. 1-3 ACH50 is a measure you would get if your home were built to code. 0.6 ACH50 (or less) is the Passive House requirement. Our home is 0.59 ACH50.

4. I want to be comfortable in my home, but I don’t want an oversized conditioning system. What do you do to ensure proper HVAC sizing techniques for an energy efficient home.

HVAC refers to the mechanicals that provide heat, ventilation and air conditioning.

This question will require a conversation with a specialty building professional (probably not your contractor), so you will need to ask who the HVAC subcontractor is. Also ask if they would be willing to switch HVAC subcontractors if the the current HVAC sub isn’t open to alternative HVAC systems. Don’t get talked into doing whatever system conforms to their line of business, and/or is the easiest system to satisfy minimal code requirements. This was one of the toughest parts of the process for us. In retrospect, we could have saved time and frustration to have XRG Concepts do a HVAC load calculation of our home. We chose a point source heating/cooling with ductless mini-split (a mini-split is a type of Air Source Heat Pump) based on key case studies, and had to fight through several subcontractors to get what we wanted. We hope that our home provides a compelling case study to help make this question easier to answer for others.

5. I want my home to perform optimally. What kind of performance metric is used to measure the energy usage of a home?

A third-party energy rater performs inspections and testing on the home and provides energy usage projections using energy modeling software. The most common performance testing used to measure the performance of a home is called a HERS Rating. We used XRG Concepts who measured our home at -3 on the HERS Index scale.