Foam-Free Air Sealing for Energy-Efficient Buildings

Presentation of air sealing strategies for high-performance buildings without relying on spray foam or rigid foam insulation.

+Ken Levenson presenting foam-free air sealing techniques for a NYC townhouse with interior insulation and a continuous “smart” vapor-retarding air barrier.

This technique is important for Passive House retrofits and should be considered best practice for any gut rehab of a brownstone where exterior insulation isn’t practical. Air tightness eliminates drafts for better comfort and reduced energy bills. It also prevents moisture buildup from condensation that can lead to mold and structural damage. Add filtered fresh air ventilation with heat recovery to optimize indoor air quality and energy performance.

Exterior insulation is preferable from a building science point of view. New buildings should be airtight, allow drying to exterior and to interior, and have exterior insulation.

The following example for a brownstone retrofit can be modified for new, non-combustible construction as well:

Integrating a window in the airtight layer – brick/brownstone retrofit case

US Army Corps of Engineers High Performance Building Envelope Symposium

March 6-8, 2012 in San Antonio, Texas: High Performance Building Envelope Symposium by the Army of Corps of Engineers and the Passive House Institute.

HPSB Flyer (PDF)

High Performance Building Envelope Workshop Draft Program (PDF)

It’s great to see the Army Corps of Engineers take such an interest in the Passive House standard for high performance buildings.

Joe Lstiburek showing two images of finned radiators, one of which won an award from AIA Chicago

The symposium featured lectures from leaders in building science (alphabetical by last name):

  • Wagdy Anis, Wiss Janney Elstner Associates
  • Lee Durston, Brown Connally Rowan Architects
  • Wolfgang Feist, founder of the Passive House Institute (by video)
  • Matthew Heron, Pie Forensic Consultants
  • Linda Jeng, Dow Building Solutions
  • Berthold Kaufmann, Passive House Institute
  • Mark Lawton, Morrison Hershfield
  • Joe Lstiburek, Building Science Corporation
  • Tomas O’Leary, Passive House Academy
  • Ray Patenaude, The Holmes Agency
  • Craig Shipp, Shwinco
  • Alexander Zhivov, US Army Corps of Engineers Construction Engineering Research Laboratory (CERL)

While the focus was on high performance building envelopes, the lectures also included discussion of ventilation with heat recovery, high efficiency HVAC systems, and mold prevention.

Based on Lstiburek’s explanation of the “perfect wall”, I like to think of the building envelope in terms of control layers, which must be as continuous as possible. From exterior to interior:

  • exterior finish (aesthetic control layer)
  • cladding (physical intrusion control layer)
  • water control layer
  • thermal control layer (insulation)
  • vapor control layer
  • air control layer
  • structure (elements can be intermittent, of course, but connections must be continuous)
  • service cavity
  • interior finish (protective control layer)
  • interior finish (aesthetic control layer)

A single material can act as one or more of these control layers. For instance, glazing performs all of these functions, including, to a limited extent, structural support.

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

Revit Content Online

A great list of Revit family content from the LinkedIn Revit Users group:

Parveen S. • Our team have been using all these website whenever required.
I hope you’ll find this information useful. (requires registration) (Requires registration) (for a fee)
MEP objects(some of the links might be outdated): from AUGI:
Acuity Brands Lighting
American Standard
A.O. Smith
Applied Air

Focal Point
Kohler (Revit families @ bottom of page)

LJ Wing | Heating & Makeup Air Equipment
Sierra | Fresh Air Systems
Temprite Industries
Loren Cook
Visa Lighting
Watts Regulator | Watts Water Technologies Inc
RPC Content
USG Wall Systems
Kawneer Curtain Wall Systems
Woodwork Institute – Casework
Lochinvar Boilers/Water Heaters:
Taco pumps & accessories:
TurboSquid (fee-based)
Reed Construction | SmartBIM Library (fee-based)
Yellowbryk (fee-based)
the list can have few more website.
though this is good enough. If you don’t find required content, create it. :)

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.