For Oct. 2nd, 2021, Metro Denver Green Homes Tour

The Duff House – Littleton, CO

1. The differences between Passive House, passive solar, and Net Zero:

“This house was designed with passive solar principles” means the orientation of the house and the placement of windows have been used to gain heat through natural daylight. Perhaps shading for hot summers was also considered. These are the first and most fundamental steps toward reducing the energy consumption of a house.

“This house was designed to Passive House principles” means that the architect and builder, of their own accord, decided to pursue a set of measurable building standards that promote low-energy consumption. The term originated from Germany’s “Passivhaus.”

“This house is a certified Passive House” means that in addition to the house’s being designed and built to the Passive House standard, it has successfully undergone a certification process. Certification is managed by various entities all over the world. The original was the Passivhaus Institute in Germany, which is still widely regarded globally. It has many partner organizations throughout Europe. (For example, here in Italy, there is work being done to address Passive House standards for Mediterranean climates.)

“This house meets Department of Energy Net Zero requirements” means that, according to the DOE’s Net Zero definition, the overall energy consumption of the project in one year is equal to the generation. This is a simple energy balance, which does not take indoor air quality into consideration.

2. Thermal Insulation vs Thermal Mass

This house has about twice as much insulation than in a regular houses. The effect of thermal mass is negligible with regards to the effect of energy efficiency. Above grade is dense-pack fiberglass. Downstairs is ICF (insulated concrete forms) with mineral wool insulation.

3. Thermal Bridging: what matters?

In terms of thermal bridging, the walls are a familiar double stud system, the roof is trussed, and there is no steel or concrete penetrating the thermal insulation. For a brief overview, check out our post – Mouse and Elephant – but for a more in depth overlook Unit 4 of our Passive House builder training program does just that!

4. High-Performance Windows & Doors

The windows in this Pilot Project are B class, triple pane, with warm edge spacers. The IGU (insulated glass unit) is Argon filled and has a low-e coating. The windows are Alpen Tyrol PH+.

5. Air Barrier – is it continuous?

One of the first things we teach our builders in our CPHT course is the “Pencil Rule” Exercise. Can you draw a line all the way around your section without lifting your pencil from the page? In Passive Houses, this is essential. In this particular project – the air barrier for the ceiling and walls is SIGA Majrex on the interior of the insulation. In the basement, the air barrier layer is the Foxblocks ICF (insulated concrete forms) and the slab on grade is lined by a poly membrane.

6. Moisture Management Strategy

All insulation above grade in this project is vapor open, with the air barrier on the inside. This is important because air exfiltration carries up to 30 times more water vapor than air diffusion, which is a commonly mistaken fact – especially when people speak of walls “breathing”. As part of Emu’s pilot program, interstitial condensation sensors have been installed.

7. Continuous Ventilation

The ventilation system is a Zehnder ERV system with continuous ventilation (“continuous” being the most important part). An ERV is an Enthalpic Recovery Ventilator, meaning it also recovers moisture in addition to heat. An HRV is a Heat Recovery Ventilator. Both are typically outfitted with F7/MERV13 filters that can filter out most wildfire smoke. Along with this, in the summer, the ventilation system has a bypass function that replaces the function of a house fan. For instance, at night during the summer the ERV system can sense when the air outside is cooler. In this situation, the heat recovery core is bypassed and cool air is brought into the building.

8. Heating & Cooling System

The heating system is a mini-split heat pump system (Pioneer) and the domestic hot water system is a split heat pump system.

9. Blower Door Test for air leakage

Blower Door Tests on Passive Houses must achieve a value of less than 0.6 AHC50. This is an extremely “tight” envelope compared to the 2018 IECC building code, which requires a 3.0 ACH50, or especially when you consider that a typical existing Colorado home is between 7 and 10 AHC50.

10. Passive House Performance

This building is expected to need 80% less heating and cooling compared to an equivalent house built to the latest energy code. All Emu Pilot Projects are certified by the international Passive House Institute and meet a heating demand of less than 4.75 kBTU/sqft/yr.

11. Passive House Team Training

The builder for this project – Bryan Williams of B-Line Construction Services – is a Certified Passive House Tradesperson (CPHT) and an alumnus of Emu’s CPHT training course. Email training@emu.systems for more info.