0.72 ach50 Before Drywall - This Home is already 90% Tighter than Energy Code

Before drywall was installed, I tested the infiltration (air leakage) at the Proud Green Home (PGH) at Serenbe, and the home achieved 0.72 ach50, or 0.055 ELR (more on these numbers in a minute). In other words, it's really tight!!! The 2009 International Residential Energy Code (IECC), which is adopted in most states, requires an infiltration rate of 7.0 ach50 or less. That's seven-point-zero. That makes the Proud Green Home 89.8% tighter than a house built to the 2009 code. The 2012 IECC, which is slowly being adopted across the country (January, 2014 in Georgia), will require homes to be 3.0 ach50. That means the PGH will be 76% tighter than a 2012 code-built house.

Gobbledygook! What is ach50 and ELR?

ACH50: Air Changes per Hour at 50 Pascals.

ELR: Envelope Leakage Ratio

Pascals is a measurement of pressure, named after the French physicist (among other things), Blaise Pascal. 50 Pascals is equivalent to the house having a 20 mph wind blowing on all surfaces of the home. This is a standard used in the home performance industry to measure air leakage in a home. Using a blower door, the house is put under 50 Pascals of negative pressure, and a manometer (pressure gauge) spits out a result in CFM50 (Cubic Feet per Minute at 50 Pascals), which tells us approximately how much air is being pulled in through any gaps or cracks.

For ACH 50, we take that cfm50 number and plug it in to a formula, based on volume, and we get numbers like 7 ach50, 3 ach50, or 0.72 ach50!! Some feel this is not the best way to determine leakage, so there are plenty of others, like ELR.

ELR is a ratio of the amount of air leakage (cfm50) and the square footage of the building envelope (SFBE). ELR is taught and promoted by Southface Energy Institute, and is considered by many in the home performance industry, as a more accurate way to measure leakage.

In plain English, the house has a hole that is about 5.5" x 5.5", and it's about 33,000 cubic feet. If this home were built to just meet the 2009 Energy Code, that hole would be 17" x 17".

For a good discussion on different ways to measure leakage, and the basics of a blower door, check out this post by Martin Holladay, on Green Building Advisor.

How did we do it? 

We have been posting videos on the construction of the PGH, showing some of the air sealing techniques, including using flashing tape at all joints between framing members, installing open-cell spray foam in all the wall and roof cavities, and using ZIP System R Sheathing on the walls and their Roof Sheathing on the roof. We've also talked about the building envelope construction including the foundation and above grade walls. All of these best practices and products resulted in a pretty tight structure.

Design a home is about architecture and building science. It's about the house as a system, where everything affects everything. For two separate Georgia homes, and for two separate builders, we have designed homes that have achieved below 1.0 ach50. The first one, the Grant Park Residence, tested at 0.77 ach50 at the final inspection for ENERGY STAR Certification. We also designed a third Georgia home that achieved less than 3.0 ach50, without the use of spray foam or ZIP System.

We're currently working on projects now where the homeowners are interested in the same (or better) performance so they can have low energy consumption, increased comfort and indoor air quality, and long term durability. We're seeing a trend...

Built Tight, Ventilate Right

It's a really good idea to design and build for a home as tight as possible. Doing so brings with it the need to provide fresh air for the people in the home, because oxygen-rich outside air is being kept from getting inside. In an earlier post, I showed you the Zenhnder America whole-house ventilation system (ERV) installed to bring in, and distribute, fresh air to the occupants. It's one of the most sophisticated systems on the market, and it's designed to keep a very well-balanced amount of fresh air through a fresh air supply in each room, and exhaust outlets in bathrooms and kitchen. It is also equipped with humidistat and other controls to help keep the relative humidity at acceptable levels.


written by Chris Laumer-Giddens

Views: 1438

Tags: ELR, ach50, air, blower, build, design, door, efficient, energy, green, More…home, proud, right, sealing, tight, ventilate


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Comment by Ed Minch on April 22, 2013 at 10:25am


For my customers, the cost of getting a tight house is right up there with actually HAVING a tight house.  We deliver houses on a production basis below 1.5 ACH50 all the time (1800-2600 ft2) without any expensive materials.  In my mind it does not matter if the leakage rate is achieved before or after drywall, it is the end result that is important.  MY own 2900 ft2 house is wet spray cellulose with an inch of foam board outside of 2X6's and is at .8 ACH50 - again no expensive materials.  We may be over thinking this.

Dr Joe has said that a practical limit is 1 ACH50.

Ed minch


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