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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This might be be far more than what you want...

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If readers haven't explored the Building America website... now's a good time to check it out.  Lots of very good papers with detailed information explaining the building science.  Tried, tested, measured and verified.

Building science people here should slow down and think before leaving harmful advice.  "Eh, maybe it doesnt matter in this climate" is low quality, or if you have skin in the game low integrity thinking.

Does the house have hvac?  Then it matters, period.   You are right, that advice does not make sense for Berkeley. My friend lives in Oakland and his house uses more energy than mine in Rochester NY, and its smaller with fewer occupants.  And it has iaq issues.  Typically the milder the climate the crappier the enclosure.

In fact there are almost no climates that dont require enclosure control.  Houses are shelter us from the environment, thinking otherwise misses the point. 

I think if you read my comments and the articles - there are many caveats that go along with the suggestions.  The original question was if the particular speaker was correct or not, what do other think. and the answer in all of my questions - is it depends on the house, the climate.  Everyone of those papers AND the very prescriptive codes you use when testing a house are based on that research.  Understand the research and the testing makes a lot more sense.


You are correct. Perhaps the LBL scientist is working in Livestock Science. Can you report his name?


This is not a LBL scientist but a city of Berkeley official in charge of energy efficiency. She made these comments in an another thread I posted earlier. 

The LBNL studies pretty much demonstrate that you have savings by tightening up a building... the size of that savings depends on the climate zone. I suspect you are in climate 4C  (marine) and building to at least the IEC 2012 should be the minimum.  Minimums are just that - they past the plans permitting processes - at what is figured to be the least cost for a region.  The minimum isn't necessarily the lowest cost over the life of the house.  You can see bigger savings by moving to the Canada R-2000 code,  or Passive House standards, however the price premium you pay along the way can increase.  Home owner life styles make a big difference on the energy use of a house - going for a Passive House certification may also mean that occupant needs to control the energy they use for the xBox, satellite TV,  PC, etc.  Those devices not only use electrical energy, but they add heat back into a house and can result in over heating on a envelope that is air tight and well insulated.

If Berkeley has adopted the ASHRAE 62.2-2013 ventilation standards, then a very air tight building is required to have a lot more ventilation.  Enough that you can potentially loose some of the benefit from being air tight.  However - the house indoor air quality is far better -- than even with windows open --!!!   The reason for the later is the recommendation that incoming air to the HRV go through a MERV filter to remove the dust and pollen.  A good filter system in the air handler plus the HRV and the ventilation can maintain a high indoor air quality... but at the expense of the power for the HRV,  and heat loss/gain in the HRV/ERV.   I believe 62.2-2013 still allows for some leakage through the envelope - and that may be what the building official was talking about.  However, you often do not know where that air is coming from,  it might be from areas with mold,  radon, etc.. pulling in air from unknown places is never as good as using a balanced airflow through an HRV/ERV.

A lot of it still comes down to the context of the conversation...  and it changes for big buildings,  hospitals, schools, etc.

Well, passive house would disagree, as well as other folks in the Seattle area. As a BPI trained individual, and IAQ consultant, I've have never heard a comment like this, sick house syndrome maybe, but not uncomfortable! What go's out needs to come in equally, every room should have a intake/outtake. 

Back to passive House, they've been doing tight homes for many years, and that has not been an issue! If you live in Sweden and Germany, most if not all houses are built this way, whether your poor or wealthy. Equality housing for all!

You have to pick one. If you want energy efficiency you have to seal the envelope. Once sealed you have to control the flow of air, in and out of the envelope. What the appropriate air flow should be is highly dependent on the house and its occupants. 

All of this is predicated by the climate in which you build. 


As an LBNL building scientist who studies deep retrofits, I can confidently tell you that (1) airtightness matters, even in Berkeley, and (2) that it is very unlikely to make a home uncomfortable (assuming you provide ventilation and appropriate conditioning and over-heating protection). In any given home (in nearly all cases), a more airtight envelope will reduce energy consumption, but that does not mean that a home needs to meet a very aggressive threshold, such as 0.6 ACH50, in order to be successful or comfortable. I assure you that I know of many successful, comfortable deep retrofits that are not that airtight. In fact, when you look across populations of deep retrofit homes, there is just about zero correlation between airtightness and either energy reductions or post-retrofit usage. We found this in our analysis of US DERs (, and the same has been found in a sample of ~30 DERs in Massachussets/Rhode Island (, as well as in another sample of DERs in the UK ( The reason is that MANY other important factors (e.g., heating system type, insulation levels, occupant behavior, set-points, etc.) are drowning out the "airtightness signal" in the cross-sectional sample of homes. This doesn't mean its not important, but it does suggest that there are many paths to success, and extreme airtightness is not necessarily required.

My two cents would be that it is a waste of money to target 0.6 ACH50 in Berkeley; you would be much better served by further investing in PV or advanced DHW or MELS controls or just don't spend the money at all. I would recommend that a gut-rehab target 3 ACH50 and provide appropriate mechanical ventilation, which includes a kitchen range hood exhausted to outside. I strongly urge you to avoid the recirculating units common in Passive Houses. And no, continuous 30 cfm general kitchen exhaust is not anywhere near equivalent.     


Thanks, Brennan.

That was the point I was trying to make.  And the Berkley building official may have been trying to suggest the same point.

Thanks Brennan for your opinion. To clarify, the question was whether or not air tightness matters for energy performance *and since we are in Berkeley, CA, does it matter for us here). The issue how much airtightness is a separate question. As I understand it the answer to the first question is YES. However, the city of Berkeley energy expert thinks that it does not. The second question of how much air-tighnes is good? is a lot more controversial and I suppose the best response will do a cost/benefit analysis to come up with the optimum level of airtightness required. Therefore, the Berkeley energy expert was NOT making the same point. On the contrary she was denying the significance of airtightness. Her thing is insulation insulation and insulation. 

Ugh,  hopefully she doesn't advocate the air filtering fiberglass insulation.

I suppose her argument is also that any house approved for construction and remodeling in California would need to meet prescriptive codes at about 3ACH50,  so she is perhaps arguing that meeting the minimal prescriptive code and loading up on insulation is better.   But adding insulation also has a diminishing return. Doubling up the insulation doesn't mean you use half as much energy. Going for R100 buys little... over perhaps R49.  

You can estimate the savings from 3ACH50 to 2ACH50 or 1ACH50.    Good builders that are used to building 1ACH50 can do that pretty economically. Builders that haven't built tight houses before can struggle to get to 1ACH50.

There are a lot of things you can trade off that also save energy when your are going from 1.0ACH50 to less than 0.6ACH50.  SolarPV might be an option (generally a more expensive route than insulation or air tight),  better HVAC,  going with LED lights,  better daylighting,  shading, etc.

The tighter the house, a good ventilation becomes with good filtering of the incoming makeup air becomes more important.  With increased balance ventilation there is an increased electrical load.  But that good ventilation (and filtered) means better healthy air also...


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