Revit and Passive House Energy Modeling with PHPP – Updated Workflow

I’ve updated my technique for using Revit with PHPP. The previous workflow used walls to create a schedule that could be exported to PHPP. The obvious limitation is that it doesn’t work for roofs and floor slabs. The new technique uses curtain panels hosted on a mass object.

Step One:

Create an in-place mass representing the thermal envelope. Do not include elements that are outside the thermal envelope, like a rainscreen or a parapet. A mass is useful to give you the gross volume and surface-to-volume ratio. And if you start modeling the building with the conceptual mass, then there is little extra work involved.

Step Two:

Host a curtain system on the mass using a simple curtain panel style. If you make changes to the mass, you will have to update the curtain system by selecting it and clicking on “Update to Face”. Assign the mass and curtain system to a future phase called “Energy Modeling” so that they don’t interfere with scheduling other building components.


Step Three:

Set up instance parameters for the curtain panels that match the required PHPP inputs. Create a schedule for the PHPP areas.

Step Four:

Export the schedule as a delimited text file with the default options.

R > Export > Reports > Schedule

Step Five:

Open PHPP and the text file in Excel. Accept the default options when opening the text file in Excel. Link the PHPP cells to the exported schedule. You can delete the text file. Excel will maintain the values when the linked file is deleted.

What’s missing is an automatic way to determine the orientation of the walls and windows. You can create a curtain panel that knows its orientation via a reporting parameter. See this video. However, this only works, as far as I know, with pattern-based curtain panels, so it isn’t as useful as having a curtain system hosted to a mass object.

Email for more information about Revit and PHPP.

Passive House consulting

Measuring Airtightness of Buildings with a Blower Door Test

Gregory Duncan performing a blower door test to determine the airtightness of a Passive House project under construction in Pennsylvania.

Use a blower door to test the airtightness of a building. For very small buildings or spaces, use a duct blaster.

Pressurization test with air flows due to leaks with negative pressure. Measuring the pressure difference in the building.

source: Passipedia

Building owners benefit from an airtight building envelope because it reduces:

  • water problems
    • a small air leak will allow a lot of moist air to get inside a wall and condense, risking structural damage and mold
  • heat transfer (heat loss in winter and heat gain in summer)
  • environmental tobacco smoke (ETS) nuisance between apartment units
    • involuntary exposure to second-hand smoke is likely to become even more of a liability for landlords in the future
  • transfer of smoke and heated gases from a fire
  • noise transmission
    • if there are air gaps, sound will find a way through the wall or ceiling assembly
    • to minimize noise between occupancies, use the airtight drywall approach (ADA) even for interior partitions

There are two main ways to document the airtightness of a building. One is to take the leakage in cubic meters per hour or cubic feet per minute and divide it by the area of the building envelope. The other method is to determine the number of air changes per hour (ACH) by measuring the leakage and dividing by the air volume. For example a 1000 m3 building with a measured air flow leakage rate of 1000 m3/h would have an airtightness rating of 1 h-1 since 1000 m3/h/1000 m3 = 1 h-1 . Using non-metric units: 583 CFM * (60 min/hr)/35,000 CF = 1 ACH. The Passive House standard requires testing at 50 Pascal while USACE requires 75 Pa. Testing at a higher pressure yields more accurate results, especially for larger buildings. (See the US Army Corps of Engineers Air Leakage Test Protocol PDF.) In order to distinguish between the natural leakage rate and the tested leakage rate at 50 Pa pressure, the airtightness number is noted as n50 or ACH50.

“Build tight and ventilate right” is a popular saying among building science consultants. Proper ventilation is essential for healthy indoor air quality, especially for airtight buildings. Building codes require mechanical ventilation if natural ventilation is not sufficient. Beyond code requirements, relying on open windows for natural ventilation can be problematic due to street noise, dust, rain, and extreme outdoor temperatures. Does a building need to breathe? That’s a confusing metaphor because there are two distinct issues. One is uncontrolled air leakage (bad) and the other is vapor permeability (usually good).

Use a blower door to find air leaks, not just to determine ACH50. Before the drywall goes up, pressurize the building with a blower door and use theatrical smoke, fingers (surprisingly effective), or an infrared camera to find leaks. The first test can be at a higher pressure to make it easier to find leaks. At this point, it might be interesting to determine the ACH50 using the Passive House methodology, but it isn’t really necessary until all the leaks have been fixed. In the US and the UK, count on three or four iterations of testing and sealing to get below the limit of 0.6 ACH50. In Austria and Germany, where Passive House construction methods are more standardized, they often just do one blower door test towards the end.

A guide to Volume Calculations for Passivhaus Air Tightness Testing and the Difference with the UK Method

Blower Door Basics

Email to schedule a blower door test and air tightness field report.

Revit and PHPP: Getting BIM and Energy Modeling Software to Work Together

PHPP—the energy modeling software for the Passive House energy-efficiency standard—requires users to input wall areas calculated to the exterior of the thermal boundary. By default Revit does not calculate wall areas this way. Gregory Duncan Architect created a workaround to create a wall schedule that can export meaningful information to PHPP.

UPDATE: Please see this update for a new method involving curtain panels instead of walls.

The following screenshot shows an exterior wall corner plan detail where a rainscreen wall assembly joins a brick cavity wall assembly. The green dashed reference lines indicate the extent of the exterior thermal insulation. This is the outside of the wall as far as PHPP is concerned.

In order to schedule the exterior wall areas with respect to the thermal boundary, create a wall type called PHPP Thermal Envelope and constrain it to the outer edge of the insulation. A green diagonal crosshatch makes it is visible when displayed with the “real” walls. This wall is in a future phase called Energy Modeling so that it doesn’t interfere with the New Construction walls and so that the New Construction walls can be used as an underlay.

Finally, I created custom wall parameters for Orientation Degrees, U-Value, PHPP Area #, PHPP Wall Group Number, and Temperature Zone and a wall schedule that can be exported to Excel and linked to PHPP.

This method is far from an ideal BIM solution, but it has been useful for keeping track of wall areas, even on a small consulting project for an architect who provided only hand-drafted drawings in PDF.

If you have any questions or suggestions for improvement, please email

Maryland wins 2011 Solar Decathlon

The University of Maryland’s entry in the U.S. Department of Energy Solar Decathlon 2011 in Washington, D.C., Saturday, Sept. 30, 2011. (Credit: Stefano Paltera/U.S. Department of Energy Solar Decathlon)

The University of Maryland won the 2011 Solar Decathlon, held at the National Mall in Washington, DC.

The U.S. Department of Energy Solar Decathlon is an award-winning program that challenges collegiate teams to design, build, and operate solar-powered houses that are cost-effective, energy-efficient, and attractive. The winner of the competition is the team that best blends affordability, consumer appeal, and design excellence with optimal energy production and maximum efficiency.

College students built the houses offsite and competed in ten equally-weighted contests:

  1. Architecture
  2. Market Appeal
  3. Engineering
  4. Communications
  5. Affordability
  6. Comfort Zone
  7. Hot Water
  8. Appliances
  9. Home Entertainment
  10. Energy Balance
University of Maryland’s Watershed House via Inhabitat

I toured the Parsons The New School for Design and Stevens Institute of Technology entry called the Empowerhouse when it was finishing construction in Hoboken, NJ. The Empowerhouse won the Affordability and Hot Water contests. It was designed to be a Passive House and will be extended and joined with another house to form a duplex. Habitat for Humanity DC partnered with the colleges and will make the houses available to low-income Washington residents.

Lakiya Culley, homeowner candidate through Habitat for Humanity, stands outside of her future residence and the Parsons The New School for Design and Stevens Institute of Technology’s entry in the U.S. Department of Energy Solar Decathlon 2011 in Washington, D.C., Wed., Sept. 28, 2011. (Credit: Stefano Paltera/U.S. Department of Energy Solar Decathlon)

Thermal Bridging

At Gregory Duncan Architect we use THERM 6.3 software—a 2-D building heat-transfer modeling tool developed by Lawrence Berkeley National Laboratory—to analyze thermal bridges.

Thermal bridges are areas in a building envelope that have higher than normal heat loss. The color infrared analysis in THERM pictured above shows a thermal bridge at the footing of a heated basement. Adding a small strip of insulation at the base of the foundation wall eliminates the thermal bridge. In this example we reduced the heat loss from a U-Factor of 0.41 W/m²K to 0.30 W/m²K by adding a 100 mm wide by 450 mm high strip of Foamglas insulation.

The next step is to calculate the U-Values for the foundation wall and the floor slab separately.

Here you can see that the concrete foundation at the right provides almost no resistance to heat loss, while the Foamglas insulation at the left prevents most of the heat transfer from the basement to the ground. The U-Value per THERM is 0.196 W/m²K.

Here a 100 mm layer of Foamglas over the existing concrete slab provides a U-Value of 0.382 W/m²K.

Then we input the U-Factor of the footing detail and the U-Values of the wall and floor into a Psi-Value calculator to determine ?, a linear heat-loss value. In this case we get 0.005 W/mK.

Using PHPP energy-modeling software we can then calculate the difference in annual heat demand for the two footing details. Multiply ? by the length of the thermal bridge to get the heat loss in watts per degree temperature difference between inside and outside. In our example, this is 0.005 W/mK * 60 m = 0.3 W/K. From PHPP we get the SI equivalent for heating degree days for heat loss through the ground for our particular climate, in this case New Haven, Connecticut. This value is 28 kKh/a, or 28,000 degrees Celsius * hours annually. So 28 kKh/a * 0.3 W/K = 8.4 kWh/a. So this detail results in extra energy use of about 8 kWh per year more than if the detail were completely thermal-bridge free. And the detail without the extra insulation results in a Psi-Value of 0.184 W/mK. Doing the math again: 0.184 W/mK * 60 m * 28 kKh/a = 309.1 kWh/a. So the extra insulation saves 309.1 kWh – 8.4 kWh = about 300 kWh per year. If heat is provided by a heat pump with a coefficient of performance (COP) of 3, that means it takes 100 kWh of electricity to make up for the extra heat loss every year. That’s the amount of energy consumed by a 100-watt incandescent lightbulb left on for 1000 hours.

So, is it worth it to add the extra strip of insulation? Depends on the incremental cost of installing it and how much value we place on reducing the energy use of the building. Assuming $0.20/kWh, 5% discount rate, period of 30 years, and 2% electricity inflation means that an investment of $392 is cost neutral, that is, Net Present Value = $0. Now, the homeowner can determine if spending more than that amount is worth it for the non-monetary benefits of reduced energy use.

Thermal-bridge analysis should be integrated into the architectural design workflow so that all major construction details can be analyzed with increased productivity.

Gregory Duncan Architect provides thermal-bridge consulting to architects, engineers, and contractors. Please contact Greg Duncan at for more information.


The Passive House low-energy building standard applies to non-residential as well as residential construction. Here’s a video in German about how to design a Passive House hospital: Energiekonzept eines Passivhaus-Krankenhauses.

 Danke am Institut für Bauen und Nachhaltigkeit

The basic principles of a well-insulated building envelope, properly oriented high-performance windows, and a ventilation system with heat recovery apply to hospitals just as much as to other building types. Hospitals use a lot of energy for computers and medical equipment, so particular attention should be paid to selecting ones with the best energy efficiency. Finally rooftop solar photovoltaic (PV) arrays can provide renewable energy and an electric vehicle fleet’s batteries can be used to store surplus solar energy. PV is not required as part of the Passive House standard, but it can reduce the building’s carbon footprint.

More Media Coverage of PHI/PHIUS Split

Ecohome, a magazine of the American Institute of Architects (AIA), continued the media coverage of the decision by the international Passivhaus Institut to end its contractual relations with the Passive House Institute US. The magazine featured a quote from Gregory Duncan and a rendering of his proposed Passive House project in New Orleans.

Gregory Duncan, a New York City architect with credentials from both institutions, says despite the organizations’ difference of opinions the benefits of building to the Passive House standard remain unchanged: “Lower utility bills, reduced noise, and better indoor air quality are just a few,” he points out.

Meanwhile, members of New York Passive House are still busy designing and building Passive House projects in Harlem, the Lower East Side, Brooklyn, upstate, and elsewhere in the region.

Brute Force

My colleague in the Pacific Northwest, Mike Eliason, at Brute Force Collaborative, has shared his perspectives on the recent split between the Passive House Institute US (PHIUS) and the international Passive House Institute (PHI), based in Darmstadt, Germany.

As an architect with credentials from both institutions, I hope the two parties can reconcile and work together in the future. Meanwhile, the benefits for homeowners and developers of building to the Passive House standard remain unchanged. Lower utility bills, reduced noise, and better indoor air quality are just a few. And for a variety of reasons, this energy-efficiency standard works especially well in New York City.

If you follow my tweets (@DuncanArchitect), you know that I sometimes spend my Sunday mornings reading German Forschungsberichte from PHI instead of going to brunch. This particular research report detailed six years of monitoring the energy use in a school built to the Passive House standard. The report confirmed scientifically that a frost skirt can allow for less sub-slab insulation. Short term monitoring and lab experiments had previously suggested that this was true, and these findings are already incorporated in the PHPP energy modeling software. Real-world monitoring to confirm the assumptions made in energy modeling software is important, and I’m glad to see that this monitoring validates the accuracy of PHPP.

The bottom line is that the scientific basis of Passive House is strong and the rift between PHI and PHIUS won’t prevent people from being able to have a certified Passive House building with lower utility bills, reduced noise, and superior indoor air quality.

Email Greg Duncan at for more information.

Multifamily Passive House Buildings in New York

The most obvious benefit of the Passive House standard is a dramatic reduction in energy costs. Using the Passive House design methodology and energy-modeling software, architects can save building owners up to 90% on heating costs compared to a typical existing building. In addition buildings built to this standard have superior thermal comfort—warm in winter and cool in summer with no drafts. A side benefit of using high-performance windows and air sealing is reduced noise from the street and from neighboring apartments. The proper architectural details can provide for acoustic insulation and energy efficiency.

Rental Buildings

Due to the expense of submetering and market expectations, owners of multifamily rental buildings in New York usually pay for heating their tenant’s apartments in addition to the common areas. By law landlords are required to provide heat between October 1 and May 31. This can be a significant expense, so developers often ask their architects to design energy-efficient buildings.

Condo Buildings

Tenants in condominium buildings often have their own heating equipment in the unit and are responsible for their own heating bills. One of the reasons condo buyers are attracted to green buildings is that they can save a lot of money on their utility bills. If the energy savings are significant, as with a certified Passive House building,  the developer’s initial investment will pay off with a higher sales price.


As an architect who has worked on townhouses in Brooklyn and Queens, as well as larger apartment buildings in Manhattan, Gregory Duncan understands the potential this type of building has for huge increases in comfort and energy savings. See our article on Passive House in New York City which explains how this green building standard is in many ways easier to achieve in New York than many other places.

Of course, the Passive House energy-efficiency standard applies to commercial and single-family houses as well. So, no matter what building type you are planning, a Certified Passive House Designer can help you make it better.

Email Greg Duncan at to get started.

International Passive House Magazine Interview

iPHM Interview with Gregory Duncan, New York, USA

Written by Tamas Banki @ iPHM on 30 July 2011
Gregory Duncan
Gregory Duncan

Gregory Duncan’s interest in high performance building began while working on a deep energy retrofit to an office building in Hamburg, Germany in 1996. He returned to the United States to obtain a Master of Architecture degree at the University of Pennsylvania. Working in New York for over ten years, Mr. Duncan has acquired a significant amount of experience with building construction.

iPHM: Tell us about yourself.
Greg Duncan: My interest in high performance building began while working on a deep-energy retrofit to an office building in Hamburg, Germany in 1996. I returned to the United States to obtain a Master of Architecture degree at the University of Pennsylvania. Working in New York for over ten years, I have acquired a significant amount of experience with building construction. Complementing this practical experience, I continually pursue advanced training in the theory of green design and building science. I am a Registered Architect, LEED Accredited Professional and one of a select group of Certified Passive House Designers in New York State.

iPHM: What did you think that time about the Passive House?
Greg Duncan: I first heard about Passive House in an article in the German magazine Detail. I researched the standard further and discovered Jeremy Shannon’s blog about his townhouse project in Park Slope, Brooklyn.
I was impressed by the ability of the Passive House energy-modeling software to accurately quantify the energy savings in a building. I joined New York Passive House and am now a member of the executive committee.

iPHM: Are you a Certified Passive House Consultant (CPHC)? What does a CPHC do?
Greg Duncan: I became a Certified Passive House Consultant (CPHC) after taking the exam last year. The official designation from the Passive House Institute for CPHC’s who are also architects is Certified Passive House Designer – Architect. A Certified Passive House Designer uses the energy-modeling software PHPP to ensure that a building meets its energy target. As an architect I use my training and experience to design the building as a whole and all the details as part of the Passive House design process.

Your country

iPHM: How well known the Passive House standard in your country?
Greg Duncan:  Green building professionals are increasingly aware of the Passive House standard in the United States. In just a few years, this awareness has increased exponentially. The first wave of early-adopter homeowners shows by example how people in New York and the rest of the country can benefit from the Passive House standard.

iPHM: How many Passive Houses are there in your country?
Greg Duncan:  Nationally, there are dozens of completed Passive House buildings. There is currently one certified Passive House building in New York and almost a hundred under construction or in planning phases.

iPHM: Is there any subsidy in you country for the Passive House?
Greg Duncan:  There are many incentives for energy efficiency that a residential or commercial building that meets Passive House standards would qualify for.


I have designed energy-efficient single-family, multifamily, and mixed-use buildings in and out of New York. I am now developing prototypes for Passive House multifamily buildings in New York City. I performed an energy analysis for a deep-energy retrofit of an historic carriage house being converted to office space at the Woods Hole Research Center in Massachusetts.