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Building Envelope or Building Enclosure: Which Is the Better Term?

building science summer camp 2012 bookshelf envelope vs enclosureIf you travel down into the building science vortex, you start discovering that people argue over a lot of things that most people never think twice about. Wait. Most people probably never think once about these things. Earlier this year I wrote about the stack effect and used the expression ‘heat rises.’ Whoa! I was nearly excommunicated on my way to Sunday School. I had awakened the Building Science Fight Club.

If you travel down into the building science vortex, you start discovering that people argue over a lot of things that most people never think twice about. Wait. Most people probably never think once about these things. Earlier this year I wrote about the stack effect and used the expression ‘heat rises.’ Whoa! I was nearly excommunicated on my way to Sunday School. I had awakened the Building Science Fight Club.

I like these discussions, though, so let’s open up another: building envelope versus building enclosure. Most people I know use the former. Joe Lstiburek prefers the latter. In a paper on vocabulary, he began, “If we don’t call things by their right names we don’t really understand how things work.” I agree. Language matters, and not just when it comes to sales.

Diving deep into definitions

But envelope versus enclosure isn’t a slam dunk like the term ‘control layer,’ at least not in my mind. According to Merriam-Webster, an envelope is “something that envelops,” and an enclosure is, “something that encloses.” But an enclosure could also be “something enclosed,” as a photograph in an envelope. That muddies the waters a bit.

Even muddier they get, though, when you consider that a fence around a pasture is an enclosure. It’s completely open on the top. It’ll keep the cows in but won’t keep deer or gophers out. That sense of the word may work for a lot of existing homes, with their swiss cheese ceilings and floors, but I think most of us would prefer buildings to be completely enveloped by appropriate control layers.

At Building Science Summer Camp this year, I asked Joe about these words. He responded, “Envelopes are for Fedex. Enclosures are for engineers.” In the vocabulary article, he wrote similarly, “They are building enclosures—they are not building envelopes. You put letters in an envelope not people.” Neither comment explains why he prefers enclosure to envelope.

A bit of history

That photo of books at the top of this article shows that the guys who did a lot of the mid-twentieth century building science work in Canada preferred the term envelope. Those are older books at Joe’s house. As I understand it, Professor Eric Burnett introduced the idea of enclosure as a replacement for envelope.

Martin Holladay, the EnergyThis house with part of the ceiling missing could have a building enclosure. Nerd at Green Building Advisor and another stickler for using proper language, discussed this in a comment of his article on Green Building Vocabulary Disputes. (See comment #4.) There he quoted from a 2003 article he wrote when he was editor of Energy Design Update:

“Burnett proposes replacing the term ‘building envelope’ with ‘building enclosure.’ At the recent Building Science Symposium in Westford, Massachusetts, Burnett said, ‘The term “envelope” does not imply the inclusion of the below-grade enclosure. It comes from curtain-wall construction, and it connotes something thin.’

That seems like splitting hairs to me. It also ignores the basic definitions of the two words, as discussed above. An envelope envelops completely; an enclosure encloses but maybe not on all sides.

According to the December 2003 Energy Design Update, Burnett also proposed replacing weather resistive barrier (WRB) with the term, ““The exterior membrane to the exterior sheathing.” Uh, yeah. Let’s replace one already-too-long term with an even longer one. I’m sure that’s gonna happen. Any day now.

What are people saying?

According to my unscientific poll on our Facebook page, 10 out of 12 people prefer building envelope to building enclosure. One prefers “enclosure-envelope. Leave off the building, please.” The other doesn’t care what you call it as long as his pipes don’t freeze. In conversations I have with other folks, most use the term envelope.

Then there are groups like the Building Enclosure Council. I’ll be doing a workshop called How to Be a Control Freak with Building Enclosure Control Layers at the Raleigh, NC chapter in January and have adopted enclosure for that event. They’ve clearly taken a position, and now the schism has moved out of our discussions and is embedded into our industry’s organizational infrastructure.

On the textbook front, Building Science for Building Enclosures, of course, takes Burnett’s term, since he wrote it with John Straube. But Green Building: Principles and Practices in Residential Construction, an introductory level textbook by Carl Seville and Abe Kruger, sticks with building envelope.

I generally use the term building envelope. I’ve tried building enclosure a couple of times, and it makes me feel smarter, part of the elite crowd. It’s like putting on a tuxedo when I say it. Sometimes it makes me want to smoke a pipe while wearing a tweed jacket with elbow patches. But I grew up more in a working class family, so I think I’ll stick with building envelope* for the most part.

The upshot

The adocates for building enclosure have made enough progress that I don’t believe that term is going away. Those of us who still prefer building envelope are numerous enough to prevent it from being washed away. It seems that the two terms will have to coexist. Both are perfectly adequate, but the existence of two terms for the same thing will create unnecessary confusion. Such is life.


*If you prefer envelope to enclosure, you then must decide on which pronunciation you prefer: en-velope or ahn-velope. Saying the latter almost gets you back to the tweed jacket with elbow patches, but without the pipe. Since both of my parents died of lung cancer, I’ll happily forgo the pipe.


Related Articles

You Do NOT Talk About Building Science Fight Club

Who Knew the Stack Effect Could Be So Controversial?

Be a Controlling Building Enclosure Control Freak with Control Layers

Green Building Vocabulary Disputes by Martin Holladay at Green Building Advisor

Vocabulary by Joe Lstiburek at

This Post Has 19 Comments

  1. Home Energy Audit sounds like
    Home Energy Audit sounds like the IRS. Envelope sounds like USPS. Joe has a point. 
    I’ll stay with E Envelope. Makes a great metaphor, I carry an Envelope labeled USPS with my Sample Kit. If I took an enclosure, I’d need another bag. 
    I would suppose we could call it a blanket! DOE actually uses that in some info. I think Joe would prefer sweater!

  2. Allison, good article as
    Allison, good article as always. To straighten this out, from now on I propose we all use term “enclolope” instead. And everybody will be happy.Sounds too intelectual?

  3. At the risk of being yelled
    At the risk of being yelled at, how about considering yet another term – “Building Perimeter”? It deals with length and distance but what the hey…

  4. Danko D.:
    Danko D.: I love it! Building enclolope should satisfy both sides and maybe even fool a few cyclopses into joining the movement.

  5. Please allow for regional
    Please allow for regional differences in pronunciation. My uncle is married to my “ahnt”, not my “ant”. Although I’ve lived in the South for over thirty years, I grew up in New England, where diction was a required subject. We’re not putting on airs. And you never hear of a pilot pushing the “enclosure”, do you? As long as the other person understands what you are saying, it really doesn’t matter.

  6. Walt S.:
    Walt S.: Good points, but you and I both know that Florida is only nominally a Southern state. ;~)

  7. Terry H., Jim S.,
    Terry H., Jim S., & Darrell T.: I see I was too narrow in my thinking. The list of candidates now looks like this: 
    I still like Danko’s idea, though:  

  8. While all sciences require
    While all sciences require some standard nomenclature, real scientists don’t take working terms too literally, IMHO, and readily understand what’s being referred to from the context, whenever terms get used interchangeably. 
    Like, for example, “measure” versus “unit” versus “metric”. Does anyone really care about, and is anyone really willing to argue over, the subtle differences in meaning of these words? Of course not. The real practitioners know which one is meant, from the context in which its being used, and are comfortable about using them relatively freely. 
    Anyone who frets too much about ascribing infinitely precise and immutable definitions to terms is really wasting their time. Next thing you know, we’ll be arguing about the real existence or non-existence of the Platonic archetypes that “building envelope” and “building enclosure” are projections of. Or something like that… 
    ~ John

  9. Either term implies one thing
    Either term implies one thing – a “boundary”. I believe this is where the true hair splitting occurs. Is this “layer” a boundary for outside air penetration (like wind), rain penetration, moisture movement, interior air movement, heat flow? Each object above is currently “bounded” by differing and varied means hence the discussion fodder. I think we might be better served if we start referring to the specific parts of the construction rather than the generic terms (e.g., is the roof a “boundary” or the interior ceiling? – answer: both). I believe it is this use of the generic terms that causes such turmoil among those who truly think about and strive to improve the several “boundary” layers in construction.

  10. Just stop it! In teaching
    Just stop it! In teaching this stuff there are so many terms, so much information that it is already overwhelming for people getting into this! What we need to do is agree on what the terms are and what they apply to. If we can’t even agree on the terms, how on earth are we going to agree on the use of undiluted CO or COAF or the area of the kitchen or the height of the building? The terms should be the simple part! Let’s put up a poll of terms and then agree on the results so we can teach consistently. . . . Please.

  11. Paul, I can’t believe you are
    Paul, I can’t believe you are dissing a perfectly ridiculous disagreement. Why shouldn’t we consume our waking hours talking about the value of words rather than actually getting the details right in the field?  
    In the hope of settling this once and for all, and for those few who remember “Rumpole of the Bailey”, I would like to propose the term “That which keeps the outside out”. No doubt about what we are trying to accomplish and you don’t have to worry about whether it is what the postman delivers or what is inside that delivery. 
    There’s a song about this too, now that I think of it. Props to first to figure out the tune:  
    Outside out, 
    Inside in, 
    Got a place 
    To drink my gin…

  12. in germany, they call it a
    in germany, they call it a huelle, which translates to shell/envelope/wrapper. and in the PH community, thermal envelope seems to reign supreme.

  13. I’m with WS and JP.
    I’m with WS and JP. Terminology is important when the wrong term could lead to confusion. But this is hardly the case here.

  14. building envelope is the term
    building envelope is the term we used in all the classes I’ve been to. 
    lets not make it confusing like the hvac companies who want to disreguard everything you say when you say supply box instead of supply boot. or lock tie instead of pundit… 
    pick one..envelope enclosure ..and move on. 

  15. Send the problem to RESNET;
    Send the problem to RESNET; they’ll have several deliberations. solicit input from the world, have more deliberations, etc., etc. and finally determine the winner. 
    They just did a wonderful job defining the word “Shall”. :^))

  16. Very good point, Stan. I was
    Very good point, Stan. I was pretty amazed to read the RESNET interpretation of a simple word that has had the meaning they came up with for 400 years. I was in a class once where the instructor was reading to the class off the very plainly written slide on the screen and kept using the word ‘may’ every time she came to the word ‘shall’. When I questioned her about her word exchange, she told me they were interchangeable…NOT. When I pointed out the difference in the two words in question, she got very irate and told me in no uncertain terms that I was wrong and she was right. I shall keep using ‘envelope’ until someone tells me not to, and actually has some negative consequences for me if I don’t follow their orders. I’m with Walt, it really doesn’t matter in this instance. 😉

  17. My opinion is that the word,
    My opinion is that the word, envelope, is so common and over used, like green roof versus vegetative roof.  
    Reliable Webster has a great definition for both: Envelope: “a set of performance limits (as of aircraft [or building]) that may not be safely exceeded” 
    Enclosure: “the act or action of enclosing.” We all know the building is at a minimum, six sided effort. 
    As an architect responsible for the design and construction effort I had rather think of this as a conscientious, active, design effort. 
    I will stick with NIBS and use enclosure if none other than it makes people think like this discussion.

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