Just Right and Airtight [Building Science]

In an article that’s sure to raise the hackles of the Passive House crowd, Joseph Lstiburek, a principal of Building Science Corporation, says the Passivhaus airtightness requirement – 0.6 ach @ 50 Pa — “doesn’t seem to be based on anything that makes any sense.”  He suggests the following: “if you get below 3 ach @ 50 Pa the comfort problems go away, things become predictable, and you save energy. Add the controlled ventilation piece and the combustion safety piece and nobody dies and nobody gets sick and life is good.”  In other words, remove large holes in the building envelope, install a controlled ventilation system, and use sealed combustion or power vented appliances. 

[+] Read BSI-053: Just Right and Airtight by Joseph Lstiburek.

Credit: The Energy Conservatory. 


  • Matt

    excellent article.  love the humor from a building science guy.  will be interesting to hear what the PH folks have to say…

    • http://www.jetsongreen.com Preston

      I agree, humorous and interesting read. 

  • Kristen

    As an architect involved with the passive house community and energy efficiency programs, I  would be thrilled to see all new construction at 3ach@50Pascal. Or even 2 or 3 times that, frankly. No hackles raised here.

    I’d also like to see significantly more building monitoring an analysis, including in situ moisture monitoring of exterior envelope assemblies. Frankly, there’s not a lot ot reseach and analysis that’s been completed on really tight buildings, whether on moisture, IAQ, etc.

  • David

    No argument here from this Passive House proponent. 0.6 is just as arbitrary as 1.5 for R2000. Just better.

  • Richardmills422

    PH in the long run will prove out. High insulation and low infiltration is the best way forward to removing  furnaces and AC not fresh air ventalation. PH homes have proven their ability to satisfy IAQ and low heating costs ten’s of thousands of times in the EU, but I guess thats a German thing.

  • Milos

    Interesting read. As a member of the Passive House movement I must say that his conclusions are rather poorly informed. First of all there are over 30,000 Passive House buildings that all were able to achieve the 0.6ACH blower door test; it’s not easy but it’s certainly possible even on a large commercial building.

    I agree with the conclusion that a house with moderately tight construction has a higher comfort level but I am sure that the energy use is not anywhere near the Passive House requirement. Currently, the Passive House standard has been assimilated into building codes all over the European Union so a lot of folks seem to think that this stringent requirement is necessary for achieving the carbon reductions that we are all striving for.

  • Richardmills422

    If you think of a house as a thermos it becomes clear. You have a tin can w/ a jar in it. how does it keep your drink hot or cold all day without insulation or external heat? Air sealing is the key, you can improve a homes performance by 15% by reducing ACH to .6 compared to code. The energy savings would pay for the added cost and an HRV day one when added to the mortgage. Mr.Lstiburek idea is to have a thermos w/ the lid off, close but no cigar.

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