It is my understanding that you need an airtight envelope (let's say less than or equal to 0.6 ACH) along with super insulation (whatever R value you need) for best energy performance. However, a building science specialist in charge of energy efficiency in Berkeley states that air tightness is (1) not important and (2) would make a house feel uncomfortable (even after a HRV/ERV system). I would like to invite professionals (building scientists, energy experts) to evaluate these views. As a non expert myself, I would like to know the truth.

Thank you!

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Kaushal, that is the typical ignorant place we all came from.  Given your account of the conversation, the extent of her expertise may be she bought a hat that says "energy expert" on it.  I doubt she's ever been involve in measured comprehensive home performance:

Hopefully she will learn as we have that insulation without air sealing often increases problems, and in fact insulation in your mild climate is the item to place less emphasis on.  Energy Efficiency isn't a product, it's a system of interconnected systems that need to be in elegant balance.  

Remember, hot goes to cold and the bigger the delta the faster the transfer.  Conversely, the smaller the delta, the slower the transfer.  More insulation to slow an already slow transfer is putting efforts in the wrong place.

Thermal mass actually works to advantage some.  Heat of the day making it's way in during cool nights.  And as others are alluding to - the tighter you get the enclosure the easier and less expensive IAQ control will be.   In San Fran you have brake dust everywhere.  Much of the time for you guys uncontrolled leaks do not mean fresh air.  The boat with lots of leaks needs lots of pumping, the boat with few needs little.

The problems I've seen with Oakland homes is leakage.  Open crawl spaces, doors you can fit bibles under, vented attics with no air seal at the thermal boundary.  Nate Adams has been writing some good stuff if you want to dig deeper:

Passive Houses by definition do not need recirculation so "...avoid the recirculating units common in Passive Houses" gives a false impression. Extraction of air from kitchens and bathrooms is a standard feature of Passive House ventilation systens.

William, maybe I miscommunicated. In my personal experience (largely in the Bay Area PH projects), as well as from my observations from the larger PH community of homes (presentations on the topic by Katrin and W. Feist), the most common kitchen system is a combination of a recirculating kitchen range hood, with a low-level, continuous ERV/HRV inlet located in the kitchen ceiling at a flow rate of 30-35 cfm. Sometimes these systems have an optional boost for the ERV/HRV. Are you saying this is not the typical system? I have seen only one PH project that used a vented range hood. Either way, my point is that these systems are decidedly insufficient and much less effective than a vented range hood, and their installation could lead to unacceptable levels of combustion and/or cooking pollutants.  

Henry David Thoreau:

"I built my cabin in the woods on Concord Pond. Then I wrapped it with 18th century plastic(bakelite like). I then encased it outside and in with rushes and 18th century extruded polyurethane equivalent thicknesses. The roof, and under the floor, also. After an hour, I found that I could barely breathe a breath as though my head was under a blanket. so I proceeded to poke a six inch hole in the wall, and inserted an 18th century exchanger made of honeycomb. On the coldest night in 1847 I was able to make it throughout the night by shivering, without addition of heat from my little stove, which would've killeth me. Thereby did I invent the field which I annointed the Natural Philosophy of Cabin Making."

Not much you can say, H.D.T was the Man!



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