There has been a bit of controversy as of late as to “how tight is too tight” regarding a building envelope. “A home needs to breathe,” some have said. While the building science community agrees with this thought, they disagree with the notion that we should let the mistakes of our contractors or the failure of our products be the cause of our homes’ breathability.

“Is that a Passive House?” She asked. The Greenfab staff was at a networking event, and I was staffing the display board for our 1300 Series prefab home when this question was asked. As a new member to the company and the industry, I desperately wanted to impress her with my recently acquired industry knowledge. But alas, my uber-honest self prevailed and I confessed my ignorance. So, she gave me a brief description of the Passive House classification I had yet to encounter and continued to explain how she didn’t like those kind of homes.  After explaining this she went on to extoll the traditionally built homes of the “good ol’ days” because they “BREATHE.”

This got me thinking…

The idea of having my home able to breathe is nice. I like open windows, screen doors, and ventilation systems. However, I am not sure how enthused I am about leaky attics, windows, and doors. Call me a control freak, but if my home is going to breath, I want to be able to control how and where it breathes.

Turns out, I’m not the only one that thinks this way. In 2005, Henri C. Fennell and Jonathan Haehnel wrote an article for ASHRAE called, “Setting Airtightness Standardswhich called for a minimum airtightness standard to be enforced for new homes. Here are some of the reasons they gave:

  • Indoor air quality: Outside air that comes in from unintended leaks can bring with it unintended contaminants.
  • Avoidance of building failures: Air leaks can cause ice dams in roofs, frozen pipes, and mold causing moisture. In fact, moisture can actually cause rot inside structural walls, which leads to expensive repairs, health risks, and even structural failure.
  • Energy Efficiency: In a typical house, air leakage can cause 25-50% of heat loss. This would be the equivalent of leaving a window open in a properly sealed home. It is possible to achieve significant savings when these leaks are sealed.
  • Building Air Security: The reality of intentional, or unintentional, chemicals being released into our atmosphere is a threat for which we must prepare.

So, with all this in mind, Greenfab decided to utilize a product called the ZIP System® on our modular homes being shown in the upcoming NAHB International Builder’s Show. Beyond increasing energy efficiency, this product decreases install time.



You will typically see house wrapping, like Tyvek®, outside walls and roof felt on a roof. The purpose of these products is to protect the home from the elements during the construction phase, and continue as a moisture barrier once the home is completed. The Zip system® (the green panels you see on the outside of the home shown above) is able to reduce air leakage by 99%, compared to typical house wrap and roof felt.

According to their website “ZIP System® wall and roof sheathing combines a structural panel and protective barrier in a complete system that offers the strength and durability of an OSB with built in moisture protection.” You can see a video about it here.

This is just one of the things we are doing in our quest to achieve a LEED for Homes Platinum rating, and to ensure our owners experience a quality product that is healthy and energy efficient.

QUESTION:  What are products or practices you would like us to incorporate into our green, prefab homes?

To learn more about these “green” strategies and others that Greenfab incorporates into each home, feel free to contact us for more information.