Advanced Airsealing Class with Industry Guru Bob Kahopka

Bob Kahopka On February 20th, 2013, a small group of EmPower contractors gathered at a typical 1920’s-built balloon-framed house in the Bronx for the field-portion of an advanced airsealing class taught by industry guru, Bob Kahopka. The home performanace contractors spoke amongst themselves about their own company methods to insulating and airsealing homes under the EmPower programs. Bob helped them to get re-aquainted with tried-and-true airsealing techniques and also taught a new technique to literally size up airleaks in local areas to prioritize airsealing efforts accordingly. This method was develped by Anthony Cox (Building Science Manager) and Collin Olsen (Physicist) in 2006 and is now being promoted for use by the EmPower program.

This new diagnostic method for determing a more effective airsealing workscope is called Zone Pressure – Series Leakage Diagnostics. It’s more effective than the typical zonal diagnostics that has been taught.

Old method: Throw a hose connected to a manometer into a room and compare the pressure found to the pressure found in other rooms relative to the main house.

New method:

1.) Run a blower door at CFM50.

2.) Throw a manometer hose into the zone that you want to test to get the pressure difference between the main house and that zone. Record that pressure in Pascals.

3. ) Go to the blower door and record the flow rate at CFM50.

4.) If the pressure difference is less than 25 pascals, open the door or window in that zone fully (until the pressure between the outside and the zone tested is “0.”

If the pressure difference is greater than 25 pascals, then open the door that is connected to the main house fully instead (so that the pressure difference between the zone and the house is now “0.”

5.) Go to the blower door and record the flow rate at CFM50 again (noting that this is with the door/ window open).

6.) Calculate the difference in flow found between Step #3 and Step #5.

7.) Mulitply the flow rate found in Step #6 against the appropriate number given on the table to find the approximate square inches of leakage between the zone and the house and the zone to the outside. Also, there is a third number on the table that can be multipled against the flow rate to find the maximum CFM50 reduction possible.

The advantage of using the new method of zonal pressure – series leakage diagnostic is that the diagnostian can now determine exactly how big the leaks are in each zone, allowing the workscope to be more focused on areas that will reduce CFM.  This is great information for the consumer who is paying for the airsealing work and wants the most bang for the buck, and for contractors who are seeking to tighten the house as efficiently as possible.

ZPDCOLOR_AC06Final.xlsThere were several areas of airsealing and insulation that were performed at the Bronx house.

IMG_60221. Order of things.

When it comes to airsealing and insulation in the attic, you want to airseal areas of infiltration first, then install the insulation. When if comes to doing that work in the walls, you want to install the insulation first (dense pack), then airseal at the appropriate places inside the house later.


 2. Using Smoke.

Smoke can be very helpful when it comes to identifying areas of infiltration (especially small ones). However, one should take caution when using it because it contains chemicals that can be harmful to those who are sensitive or have respiratory problems. It is more helpful to pressurize the house when using smoke on the inside of the house so that the area of leakage is sucking on the smoke, not blowing the smoke generally back into the living space.


3. Insulating the slopes of an attic.

When insulating the slopes of an attic, open-cell spray foam is a great product to use because it gives one of the highest r-values per inch and allows homeowners to detect roof leaks before closed-cell spray foam does. It also acts as a great air barrier and prevents convection.




 4. Airsealing at an INTERIOR wall.

Airsealing the top plate of an interior wall from the attic plane that communicates with the conditioned space will cut down on infiltration and occupant discomfort. Even though the thermal and pressure boundaries are defined at the very edges of the house, the attic will inevitably see infiltration from the outside and bring drafts down chaseways, even those located at the interior of the house.


At the end of the field day, after spray foaming the attic and dense packing the exterior walls, we ran a blower door test at CFM50. We found that we cut down flow by about 1404 CFM – from 5295 CFM50 to 3891 CFM50, which is just slightly above BAS (Building Airflow Standard). No need to consider mechanical ventilation.


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