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My Choice in the ‘Building Enclosure’ vs. ‘Building Envelope’ Battle

Max Planck Physicist Nobel Prize Winner

When I wrote about the debate over the terms ‘building envelope’ vs. ‘building enclosure’ a couple of weeks ago, I favored the former but overall felt agnostic on whether we should choose one over the other. I didn’t think I’d change my mind. After reading the many comments from readers here in the Energy Vanguard Blog and in the two LinkedIn groups where I posted the article as well, I have indeed decided that we should go with one of the two terms and abandon the other.

Although I’ve framed this debate as being between only the two terms I mentioned above, some of the commenters suggested other terms as well: building fabric, building shell, and building perimeter. Some also proposed a compromise approach using a combination word: envelosure or enclolope. Another contingent said it doesn’t really matter what you call it as long as the meaning is clear to all parties.

Here’s why I think it does matter, though. Building science is a young science, crafting its own identity only in the 20th century. In contrast, physics has been around for thousands of years, and a lot of the material students learn in introductory physics classes is hundreds of years old. The battles over the fundamental terms is long over in that most fundamental of the sciences but still raging in one of the newest, building science.

It’s important for experts in a field to agree on the terminology for ease and clarity of communication. Although the majority of people see ‘speed’ and ‘velocity’ as synonyms, for example, every physicist knows there’s an important distinction (velocity includes the direction) and uses the correct term when speaking about motion. ‘Envelope’ and ‘enclosure’ don’t have different meanings (yet), but it’s still important to choose one.

Max Planck, the physicist who first recognized the quantum nature of radiation and whose portrait is shown above, once wrote:

“A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather its opponents eventually die, and a new generation grows up that is familiar with it.”*
~ Max Planck

This may not be about a scientific truth, but those who write the building science textbooks and teach the building science courses seem to have made their choice already. Their term is ‘building enclosure.’ As the field develops, more and more people will be exposed first to that term, and those who prefer ‘building envelope’ or other terms will die out.

Well, OK, that may not be exactly how it plays out, but I do think ‘building enclosure’ is the better term to use. I’ve resisted it up till now because I was more comfortable with ‘building envelope’ and because I wanted a better reason than “Envelopes are for Fedex; enclosures are for engineers.” Here’s what’s changed my mind:

  • It’s confusing to have multiple terms in use for the same concept, especially one as fundamental as the boundary between conditioned space and the various types of unconditioned space.
  • ‘Building enclosure’ is already taking over the building science programs.
  • I now believe ‘enclosure’ is a better word for this concept than is ‘envelope.’

Precision of language matters. The building enclosure is one of the most fundamental concepts in building science, and it does make sense to use a single term term to describe it. I’m now a convert to ‘building enclosure’ and will use it exclusively.


* This statement contains an ironic twist because Planck refused to accept the wave mechanics of Bohr, Heisenberg, and Pauli and became one of those old guys who couldn’t see the light, thus proving his statement correct.


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This Post Has 26 Comments

  1. OK … I believe they are two
    OK … I believe they are two different animals that are often the same. Lets take a commercial building or apartment complex with an exterior elevator shaft, enclosed (not conditioned) exterior staircases with no weatherstripping on the entry doors, and common hallways. All of these would be within the building enclosure but probably none within the envelope. The building envelope refers to the air barrier system & enclosure refers to the bricks & mortor. 
    Another example would be buildings where the attic floor is insulated … that floor delineates the envelope but the roof delineates the enclosure … makes sense to me.

  2. Paul M.: I
    Paul M.: I follow your logic and agree that enclosure could be used for what most people call the shell. I’m going with enclosure because I think, in the end, it’s going to be the winner.

  3. Allison Bailes:&quot
    Allison Bailes:”Precision of language matters.” 
    Julius Sumner Miller:”Hot air does NOT rise…hot air is pushed up by cold air falling in from below…So, I emphasize the need for using the language like heat and temperature and such with exactness, otherwise they lose their proper meaning” 
    7th RULE: Fights will go on as long as they have to.;-)

  4. John B.: I
    John B.: I almost mentioned the stack effect in this article and then thought better of it. Perhaps I should revisit that topic, but I’ll just say here that ‘rise’ means to move upward. There’s no cause ascribed; it’s just about motion. If heat is moving upward, whether it’s being pushed or through some other action, it’s still rising.

  5. If we can change “Houses
    If we can change “Houses need to breath” or “Hot air rises”, what’s one more “Building Envelope”… Meany of us have already “brainwashed” by Dr. Joe, but I’m sure it won’t take long before others change as well.

  6. Why wasn’t the term &quot
    Why wasn’t the term “shell” included in your previous article? Then, we could’ve debated about selecting between three popular terms, rather than just two.  
    Why did you whittle the candidate list down to only two runner ups, before launching into this debate in the first place? 
    My point is, you’d probably already decided, based on some internal, personal bias of your own, that “shell” wasn’t even a candidate, and two terms you liked better, were. 
    I’d agree that every body of science requires a standard and precise nomenclature in order to work. But personally, I tend to be a functionalist (ala Wittgenstein) when it comes to language and meaning: i.e., the meaning of a term is determined solely by how it’s most often used in meaningful discourse, by some population of practitioners. 
    Just because some body of discourse has several synonyms that are more or less interchangeable doesn’t automatically make them imprecise. They still get used in the same way, with the same results. 
    Arguing over one established synonym versus another reminds me a bit of those folks in Gulliver’s Travels who went to war because they couldn’t decide whether or not to open their eggs at the small or large ends. Functionally, either end got the job done. 

  7. Armando:
    Armando: Well, ‘brainwashed by Dr. Joe’ isn’t a terrible thing, especially if single malt scotch is involved. I actually resisted that, though, and it took a lot of thought to overcome resistance to ‘enclosure’ just because I didn’t want to be brainwashed. 
    John P.: Ah, yes, I guess I’ve never really explained why I don’t like ‘shell’ for this concept. John Krigger and the Saturn crew do like it, however, and use that term exclusively, so there is at least one important player in the field pushing for ‘shell.’ I’m not in favor of ‘shell,’ though, because I consider it to be the outer layer. The roof, for example, is always part of the shell but not always part of the building enclosure.  
    You do make a good point about either term being acceptable, and I was in your camp until recently. I’ve decided to go with ‘building enclosure’ because I believe that in the long run, it’s going to be the winner. 

  8. Apologies that I am late to
    Apologies that I am late to the discussion. I wanted to comment on the first post but I am, uh, busily wrapping up an important project. 
    I prefer enclosure for the reasons you stated above. However, 
    No matter what term we use when speaking to each other (jargon) -allowing us to speak clearly, efficiently and quickly, there is danger when we are speaking to someone outside our group. This is not to say we would intentionally use jargon, knowing that the non-group member has no idea what we really mean by enclosure (Thank you William Lutz and your essay “Doublespeak”. The real danger is assuming they do.  
    The Lutz priorities are in the proper order. Speak clearly. Speak efficiently. Speak quickly. No matter who you are communicating with. That is the mark of a real teacher and master of this science.

  9. Hi Allison, 
    Hi Allison, 
    Actually, I personally prefer “enclosure” myself.  
    My point focused more on the nature of the debate itself, rather than the terms, because, quite frankly, these kinds of issues of language and semantics and meaning interest me enormously. 

  10. Allison,  

    How can a roof not be a part of the “enclosure”? The primary function of a building enclosure is to separate the inside from the outside. While a roof may not provide the main thermal separation between inside and outside, but it certainly provides the most important separation – it keeps the rain out.

  11. Allison, 

    Good fun writing as usual – I would typically use both terms as Paul McGovern stated in the comments. With your new conversion to the religion of the word enclosure do you agree with his comment or what? Is there a good definition of this word you recommend. 
    FYI – I don’t care but do want a consistent set of terms to use so I can get along on the important work of saving the world. One building at a time.

  12. Jeff M.:
    Jeff M.: Clarity is critical. Yes, every field has its jargon, but when speaking to those not in the know, we must define our terms. 
    John P.: I think you know that these discussions interest me enormously, too. 
    John S.: As Jeff pointed out, we’re in the realm of jargon here, and terms don’t always have the common meanings. Velocity to a physicist, as I mentioned, means something different than it does to most people. Enclosure is being conscripted to do what I learned as the building envelope. I use the term shell for the outer layer that keeps the rain out and now enclosure for the part that wraps up the conditioned space. I could easily have made different choices, but I’m going to go with the folks who are writing the building science textbooks and training new building scientists. 
    Jason Q.: No, I don’t use the words the Paul McGovern described. What he calls ‘enclosure,’ I call ‘shell.’ What I now call ‘enclosure,’ I used to call ‘envelope.’ The definition, which I should have provide in the article, is:  
    Building enclosure – the boundary between conditioned space and the various types of unconditioned spaces (ambient, attic, ground…) that surround it. The building enclosure is composed of the air and thermal control layers, which should be in contact with each other.

  13. This definition of Building
    This definition of Building enclosure is equivalent to what I would typically have called the thermal envelope (I’ve no issues with Thermal enclosure also called Building enclosure). 
    This can coincide with the air tightness layer (air tightness enclosure now?) and weather tightness layer (weather tightness enclosure?) but often does not.  
    Thanks for the definition. 
    English – yes it’s how we communicate.

  14. And here’s Joe Lstiburek’s
    And here’s Joe Lstiburek’s definition, taken from his article, Vocabulary
    Building enclosure – the system or assembly of components that provides environmental separation between the conditioned space and the exterior environment. Note: The enclosure is a special type of environmental separator. Environmental separators also exist within buildings as dividers between spaces with different environmental conditions.

  15. Your previous post got me
    Your previous post got me thinking about the importance of consistency in communication. You make a very good case for that here. I think it matters less as an internal conversation amongst ourselves, the building science crowd, than it does when we are talking to building owners and occupants. We understand each other (well, sometimes) and we understand the concept well enough so that a slight change in wording doesn’t affect that. 
    It does matter to the people we should be educating on this stuff. Teaching is about clarity. The only way we will project that is if we give up the disparate terms and settle on a clear definition. 
    I’m tossing my vote to enclosure as well. I think it’s less ambiguous and you don’t have to lick it to keep it closed. I don’t like shell because to me it connotes something easily cracked. I like my enclosures to be robust.

  16. really? 

    to me it seems to be much ado about nothing.  
    even if a definitive term is chosen..there will be people who chose to use the other term. just to be contrary.  
    it is this way in other box vs supply boot. and it is clearly a hvac trade 
    sole plate vs bottom plate 
    in building trades. 
    as a woman in this field I have come across many things with multiple names. 
    to add more terms that mean the same thing..only confuses the issue. 
    we are trying to do our work the field.. 
    not sitting behind our desks creating new terminology .. 
    which confuses what we are trying to explain to the general public. 
    I get called old school by new people in my trade. old equipment isn’t brand new, I can find insulation voids in the attic without a thermal scan…by doing the visual inspection.  
    so now building envelope will be old school, and the new folks will use building enclosure. 
    there is already enough problems in breaking down building science to joe public. to add changing terminlolgy to this mix.. 
    seems like just a waste of effort to me, and it confuses the issue. 
    of all the topics to address this should be low on the list of pirorities. 
    implementing the science not just nitpicking about terminoloty should be the priority. 
    and the whole mixing two words to create another one? if it isn’t in the isn’t a word. we have enough destruction of english going on with out adding to it. what are we..12 that we create words? 
    just amazes me that this even rates space in an otherwise useful blog. 

  17. Bill S.:
    Bill S.: You make a good point about the extra meaning behind the word ‘shell’ that I hadn’t thought of. Glad to hear you’re making the switch, too! 
    Debbie: Yes, of course, people will continue to use ‘envelope’ and ‘shell’ and perhaps other terms, too. I’m perfectly fine with that. I also realize that some people see this as ‘much ado about nothing,’ but I think it’s important. I didn’t do a good job of conveying that the folks who suggested the combination words did it in jest, so you don’t have to worry about the enclolope and envelosure crowds trying to get their way. ;~)  
    Stay tuned, though. This ‘otherwise useful blog’ has plenty more to say that you’ll find useful, I believe.

  18. My personal preference is
    My personal preference is “thermal boundary”. This “boundary” may or may not be separate from sun, water, and wind boundaries, or what we commonly call roofs and walls.  
    Now whether “thermal boundary” implies airtighness and water vapor control alongside any insulation properties…that seems to a be similar concern that might arise in “envelope/enclosure” discussion. According to Dr. Joe, an air control layer does not always need to align with the insulation. In such a case the term “thermal boundary” would seem more literal…it’s controlling heat flow but not immediately controlling air or moisture flow. Hmm…

  19. I’ve always been a fan of
    I’ve always been a fan of “shell” and I’m sticking to it! I think it has the best crossover to layman’s (homeowner’s) terms as well…

  20. I prefer to think Allson has
    I prefer to think Allson has been brainwashed by his wife–as well as Dr. Joe. Seriously, the poet in me thinks that  
    “enclosure” is a much better word choice. Hopefully, you building science nerds aren’t just talking among yourselves; you want to talk to a larger audience. If you are going to sell us services and materials, you need to speak in a way that is easily understood by as many consumers as possible. 🙂 

  21. As a homebuilder, I read a
    As a homebuilder, I read a lot of books about homes and residential structures. I have noticed that many of the terms used to describe the building’s parts or a particular process are regional. This may fade away as out language becomes homogenized by the internet and television (YouTube.) In my part of the country, the foundation walls of a home are supported on a footing, and in other parts of the USA it is a footer that is placed beneath the basement wall. Many people speak of and even company names use the word cement to describe what is now commonly called concrete. And the exact meaning of a cripple and sleeper are really hard to pin down. And around here we never “dry-in” a building. We just move right past that step and put the shingles on top of the felt on top of the sheathing and we call it being “under roof.” And when a customer does not understand me, i tell them we put the shingles on yesterday. Do you call it sheeting, or sheathing? Some people just want to stick with the word cellar when around here, we call it a basement. 
    I learned the word Envelope, long before I heard it called an Enclosure. And my father always called air coming into the house “infiltrations, but lately it seems to be called Bypass. Is this really the difference between the air that comes in or goes out and the hole it goes through? 
    In the end, I agree entirely with Allison. Precision in the use of the language of building science really is important.

  22. Interesting to hear about Joe
    Interesting to hear about Joe’s brainwashing in fact Joe heard the term Building enclosure from his mentor’s and not him. Eric Burnett used the term back at Summer camp in 2002. Ther term Seperators was used by Doctor Ted Kesik in Toronto Canada when he taught me Building Science at Ryerson University, the Building science course was actually called seperators where he taught us thermal performance and hygrothermal performance of foundations, walls and roofs. He is one of the best Building scientists out there and very good proffesor. Guess what he loves wine too. It must be a Canadian thing, Eh! 
    I will always use the term Building Enclosure, its the most appropriate technically and literally.

  23. The term “building
    The term “building envelope” indeed does have some ‘value’ for me as a indicator or gauge of sorts. It’s the same gauge that registers when someone says ‘cement steps’ instead on ‘concrete steps’. It helps me fine tune my delivery to my audience. Knowing and understanding my audience better helps me. If someone uses the term ‘building enclosure’ on the other hand, I pretty much know that I don’t have to spend time on basics, etc – that there is a good chance this person has a deeper understanding. It’s not 100% valid, of course, but if you eliminate ‘envelope’, I will have lost a small advantage. 🙁

  24. Hello, 

    Being very critical on wording in my old age makes this all come together. This all makes sense from a pure experience stand point, different words mean different things to individuals in an audience based off their exp too. Outer structure could be a viable option to envelope where defined as if the other side of it meets the outside air. 
    Thank you all for the volumes of knowledge and insight. The only thing I was disappointed about is not one of you asked “How do you like them Apples”.

  25. John Straube’s students
    John Straube’s students converted me over to Enclosure some time ago so I am glad to see agreement on that term which seems correct.

  26. When I am discussing with
    When I am discussing with clients, I differentiate between the thermal barriers and building barriers when they are different.  
    When I took the HERS class with Allison and Mike, the term used was building envelope or thermal envelope.  
    I use both terms NOT interchangeably but very specifically when speaking with my clients. We all end up on the same page with those terms.

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