Recently I was asked by a reporter to talk about my number one wish list item that I wish was better understood by homeowners in light of climate action and sustainable concepts that support the big picture of carbon reduction. Here is my reply:

In Minnesota, homes consume the largest chunk of energy during the winter months in form of heating energy. Each unit of energy has a carbon output associated with it. Home energy performance is largely driven by the quality and performance of the building envelope—components such as basement floor, exterior walls, roof, exterior doors and windows that separate inside from outside. I see that homeowners can get confused about how to improve home energy performance, and often gravitate towards mechanical systems, or renewable energy systems instead of improving the building envelope.

 

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Highly insulated wall with German-made triple pane window at the MinnePHit House in Minneapolis, MN—the first certified Passive House retrofit project (EnerPHit) in a cold climate zone (TE Studio, 2011).

A simple comparison with everyday life: While the building envelope compares to the heavy down jacket Minnesotans wear in the winter, the mechanical system compares to the little heating pouch we stick in our pockets to warm our hands. Most Minnesotans would agree that when venturing outside in the winter, the heavy jacket is more important than the little heating pouch, and understand that they would need a mighty large pouch to make a summer jacket keep them warm instead.

Similarly, mechanical equipment plays a role in home performance, comfort and efficiency but it cannot set the baseline for performance and improve the bottom line. Fact is that most humans prefer 70 F at 40 – 50 % relative humidity, which is a condition that we rarely encounter outside in Minnesota—particularly in the winter. It is the building envelope’s job to protect us from the elements, and enable the building to maintain those preferable conditions inside. Whatever the building envelope cannot do, a mechanical system has to compensate for. In return, this means that the better the building envelope, the less the mechanical system has to provide, the less energy is being consumed and has to be generated, and the lower the carbon footprint. At the same time, comfort is up as the human body enjoys the steady environment.

A greater understanding of these facts enables homeowners to make sound decisions when it is time to enhance building performance—either for comfort, financial, or environmental reasons, or just because the building envelope is up for routine maintenance, which—by the way—is the best time to make upgrades as upgrade costs become incremental to the maintenance work.

The same is true for new construction, as our building energy code sets a comparatively low bar for building performance and comfort (you would not wear that summer jacket in the winter). The nice thing about building envelope upgrades is that they return on their investment on many levels all at the same time: Reduced carbon footprint, reduced energy bills, and increased comfort. In short, they are a smart use of our finite resources.

For those wondering what these upgrades entail, it is pretty simple:
  • More insulation than code (typically 2 – 3 times); a checklist approach could be adopted, or an energy model used to determine the exact amount
  • Airtight construction of less than 1 air change per hour at 50 Pascals pressure (measured with a blower door in the field); airtightness is an insurance policy against early building degradation among other things
  • High-performance windows and doors (overall installed U-factor of less than 0.14 BTU/ h sf F with a solar heat gain coefficient of around 50% and an exterior shading strategy)
  • Hygrothermally sound assemblies (meaning moisture transfer is understood and the design for the building envelope is resilient and durable over time)
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Secondary wall framing ready for insulation during construction.

A qualified professional such as TE Studio can assist with goal-setting, design and planning, which is key to a successful implementation of building envelope enhancements.

It is understood that plug loads and domestic hot water also play a big role, particularly in regards to the carbon footprint of a home. However, those loads are often much more user-driven and therefore more challenging to address by design. As an architectural-engineer, I therefore focus my attention on the parts of the building our profession can control and encourage energy-aware living among those I work for, or talk to.

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