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Green Building Vocabulary Disputes

Watch out — sloppy terminology may earn you a scolding from the word police

Posted on Jul 23 2010 by Martin Holladay

As any builder knows, construction terms vary from job site to job site; one carpenter’s furring strip is another carpenter’s strapping. Like carpenters, building scientists are inconsistent when it comes to technical terms — in part because building science is a relatively young field.

In new fields of learning (including building science), vocabulary generally wanders at first, and eventually converges once consensus is reached. Reaching agreement on technical terms is useful. It helps achieve a desirable goal: efficient communication.

Some people cling tightly to their favored vocabulary and resent efforts to encourage consensus on technical terms and definitions. That’s fine, as long as no misunderstandings result.

Unless you’re a word junkie, you may roll your eyes at some of the technical disputes listed in the table below. After all, who cares whether WRB stands for “weather-resistant barrier” or “water-resistive barrier”? (Just help me nail up the freakin’ housewrap, okay?)

Other readers will delight in these debates. For interested readers, these disputed terms may be food for thought.

For the record, I’m not necessarily in favor of all of the terms in the “preferred” column. Many of these vocabulary disputes are not yet resolved. In the meantime, the words we choose should communicate our meaning clearly. Adopting an unusual (though technically correct) term doesn’t improve communication if it leaves the listener or reader confused.

Last week’s blog: “One Air Barrier or Two?”

Out-of-favor term Preferred term Comments
Air-to-air heat exchangerDevice that transfers heat from one material or medium to another. An air-to-air heat exchanger, or heat-recovery ventilator, transfers heat from one airstream to another. A copper-pipe heat exchanger in a solar water-heater tank transfers heat from the heat-transfer fluid circulating through a solar collector to the potable water in the storage tank. Heat-recovery ventilator(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. The industry reached a consensus on “heat-recovery ventilator” two decades ago.
ECM motor ECM “ECM motor” is redundant, since ECM stands for “electronically commutated motor.”
Energy-recovery ventilator Enthalpy-recovery ventilator Enthalpy accounts not only for sensible and latent heat but also mass; however, purists are unlikely to prevail on this one.
Geothermal heat pumpHeating and cooling system in which specialized refrigerant fluid in a sealed system is alternately evaporated and condensed, changing its state from liquid to vapor by altering its pressure; this phase change allows heat to be transferred into or out of the house. See air-source heat pump and ground-source heat pump. Ground-source heat pumpHome heating and cooling system that relies on the mass of the earth as the heat source and heat sink. Temperatures underground are relatively constant. Using a ground-source heat pump, heat from fluid circulated through an underground loop is transferred to and/or from the home through a heat exchanger. The energy performance of ground-source heat pumps is usually better than that of air-source heat pumps; ground-source heat pumps also perform better over a wider range of above-ground temperatures. The term “geothermal” is best reserved for phenomena like geysers and hot springs.
Green roofRoof system in which living plants are maintained in a growing medium using a membrane and drainage system. Green roofs can reduce storm-water runoff, moderate temperatures in and around the building (by providing insulation and reducing heat island effect), as well as provide a habitat for wildlife and recreational space for humans. When properly constructed, green roofs can increase roof durability because the roof assembly’s air and water barriers are buffered from temperature fluctuations and UV exposure. Vegetated (or living) roof “Green” has so many meanings that its use in this phrase is imprecise.
Heat exchanger Heat transferer Proponents of this substitution point out that heat is transferred in one direction, not two; however, “heat transferer” has not caught on.
Permeance of a material Permeability of a material “Permeance” is used when discussing a sample of a defined thickness; “permeability” is a material property independent of thickness.
Photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. panel Photovoltaic module A photovoltaic module is made up of a number of photovoltaic cells; a photovoltaic array contains several modules.
Return-air register Return-air grille Registers include dampers, while grilles do not. Of course, return-air grilles do not require dampers.
Sealed crawl space Closed crawl space Consultants from Advanced Energy in Raleigh, NC, prefer “closed crawl space,” since a closed crawl space can work well even without extraordinary air-sealing efforts.
Solar panel Photovoltaic module or solar thermal collector “Solar panel” fails to distinguish between two different technologies.
Solar photovoltaics Photovoltaics In this phrase, “solar” is redundant.
Tankless water heater Instantaneous or on-demand water heater “Tankless” introduces possible confusion with old-fashioned tankless coils.
U-value U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value. Technically (and mathematically) speaking, this number is best described as a factor, not a value; at least the NFRC gets this one right.
Vapor barrier Vapor retarder “Vapor retarder” (or, for the truly precise, “vapor diffusion retarder”) is the best term for materials that slow the passage of water vapor; “vapor barrier” should be reserved for materials with a permeance of 0.1 perm or less.
Vent Grille, register, air intake, exhaust outlet, flue “Vent” is vague, except in phrases like “soffit vent” and “ridge vent”
Weather-resistant barrier Water-resistive barrier The International Code Council Evaluation Service voted that “WRB” shall henceforth stand for “water-resistive barrier.”
Dense pack cellulose Dense-packed cellulose Just as a difficult battle is a “hard-fought victory,” not a “hard-fight victory,” cellulose that has been installed tightly is “dense-packed cellulose.”

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Jul 23, 2010 6:44 AM ET

by John Brooks

When I first read the title of this Blog
I thought you were going to talk about Joe's Vocabulary
Enclosure vs Envelope
Water Control Layer vs Weather Resistive Barrier
Ginger vs Mary Ann

Jul 23, 2010 7:42 AM ET

Sealing the deal
by James Morgan

Clarity of language, that precious jewel. Thank you Martin for this.

There's one comment I didn't quite follow. "Consultants from Advanced Energy in Raleigh, NC, prefer “sealed crawlspace,” since a closed crawlspace can work well even without extraordinary air-sealing efforts." Did you mean to write that they prefer "closed crawlspace"? That would seem to make more sense with the explanation that follows.

Jul 23, 2010 7:53 AM ET

Response to James
by Martin Holladay

Thanks for catching an editing mistake. You're right, of course. I have made the correction in the table.

Jul 23, 2010 8:15 AM ET

Response to John Brooks
by Martin Holladay

As I wrote above, many vocabulary disputes remain unresolved. Joe Lstiburek (like Eric Burnett) prefers “building enclosure” to “building envelope.” But I have no problem with “building envelope.” I reported on some of these vocabulary disputes in the October 2003 issue of Energy Design Update, where I wrote:

“Eric Burnett, the director of the Pennsylvania Housing Research Center, is concerned that many of the terms used by building scientists have been adopted without due care. After an initial assault on ‘weather-resistive barrier’ (see EDU, April 2003), Burnett has broadened his crusade for vocabulary reform with public attacks on ‘building envelope,’ ‘reservoir cladding,’ and ‘redundancy.’

“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.’

“However, the word ‘enclosure’ is no more likely than ‘envelope’ to evoke the inclusion of a building’s sub-grade shell. Among the dictionary meanings of ‘envelope’ are ‘the bag that contains the gas in a dirigible or balloon’ and ‘any enclosing membrane, skin, shell, etc.’ These definitions are not far off the mark in the context under discussion. The definitions of ‘enclosure,’ a word with agricultural origins, include ‘something that encloses, as a fence, wall, etc.’ The image evoked by ‘enclosure’ -- a fenced pasture -- is more two-dimensional than the one conjured by ‘envelope,’ especially in the special sense used by balloonists.

“Burnett would like to replace the term ‘reservoir cladding’ -- a Joe Lstiburek coinage describing any siding that absorbs moisture -- with ‘storage cladding.’ According to Burnett, ‘When you think of a reservoir, you think of lots of water. But such claddings don’t necessarily have to store much moisture. It can be either a lot or a little. That’s why the word “storage” is better than “reservoir.” ’

“Yet the word ‘storage’ gives rise to the unanswered question, ‘What is being stored?’ The term ‘reservoir,’ on the other hand, clearly evokes the concept of water storage -- as opposed to, say, thermal storage.

“Finally, Burnett would like to banish the use of the adjective ‘redundant’ to describe secondary barriers to water penetration. Burnett notes, ‘“Redundant” means “superfluous.” One could say that a building component is there as a reserve, or for safety, or to reduce risk, or “just in case” -- but we should never use the word “redundant.” ’

“Here the professor is on firm ground, and EDU is willing to stand shoulder-to-shoulder with Eric Burnett in the battle against ‘redundancy.’ ”

Jul 23, 2010 8:17 AM ET

We'll alll have to practice saying 'vegetative'
by James Morgan

On GBA's home page immediately below the headline for this blog entry I see this item:

"Green Roof Plants
Green Roof Plants (Emory Knoll Farms) is the only company in North America known to specialize solely in plants for extensive (low-profile) green roofs. In operation for six generations, the company has shifted production solely to green roof applications."

The article is actually a good example of the kind of sloppy writing that Martin seeks to address - sorry GBA but if your best friends don't tell you who will? It continues: "The company's greenhouse is powered by a 3 kW PV system, and solar power also powers water pumping." The solar radiation that actually supplies most of the input energy to their growing house (do they really only have just one?) is much greater than 3 kW and does not come from the PV array. The PV system presumably supplies energy merely to the building's lighting system, a very small component of its total energy needs. Given this audience it might also be nice to know *how much* of their lighting and pumping needs are supplied by the photovoltaics. 100%? 50%? 5%?

Oh, and see what I did there? 'Greenhouse' is, well, confusing in a forum that discusses 'green houses' extensively, if vaguely. 'Glasshouse' is a traditional alternative that is largely out of date now that most of them are plastic. Can we make a case for 'growing house' as a specific descriptive?

Jul 23, 2010 8:38 AM ET

Vapour Control Layer
by Brian O' Hanlon

Martin, as usual you blog entry got me thinking, and as my response got away too long and complex, I decided to post it over in 'Green Building Techniques' to solicit further comment.

Jul 23, 2010 8:48 AM ET

Response to James Morgan's second post
by Martin Holladay

Excellent post! Keep it up! All of your points are observant and appropriate.

As you can imagine, GBA is a sprawling Web site with contributions from dozens of authors and staff members. I haven't had a chance to review everything on our site yet, and the page you referred to definitely needed some copy editing. Your suggestions were good ones, and I have already made several corrections to the page in light of your comments.

As far as "growing house" is concerned -- I think I'll wait on that one. "Greenhouse" is a very common word, well entrenched in everyday speech, and is unlikely to be uprooted and replaced easily.

Jul 23, 2010 2:57 PM ET

by Michael Blasnik

tankless water heaters are not instantaneous -- they actually take longer to produce hot water than having a tank. I think the trend in usage is toward tankless, as it should be.

Jul 23, 2010 8:06 PM ET

sloppy terminology
by Jorg Breuning

In most „cases” it isn’t sloppy. It is misleading on purpose. Very common in the US – even my company is taking advantages of this technique and the general green confusion in the American market. In Germany where most of these technologies are standardized since decades the terminology is also standardized – not only in standards. This helps to make more sale since the clients know what they can expect and get.
Since I am German I might take advantage of it…:
Our company is the only company in North America known to specialize solely in German technology for high-profile green solutions. In operation for 18th generations of Germans, the company has shifted services solely to the USA…..
…it is not experience and education it is only in the genes.

Jul 24, 2010 1:51 AM ET

passive house & passivhaus
by mike

really wish the US would adopt the UK/IE method of calling a passivhaus a passivhaus, thereby avoiding many ridiculous arguments and articles about why a passivhaus is not necessarily a passive solar house, etc. i think it would have made the intro to the states a little smoother and confused significantly fewer people.

Jul 24, 2010 5:09 AM ET

Response to Mike
by Martin Holladay

I agree with you completely on the importance of distinguishing between a passive house and a Passivhaus. Since I first began reporting on the Passivhaus standard in February 2004, I have tried to be consistent and refer to Passivhaus buildings using the German spelling. It is a courtesy to readers.

Unfortunately my aim for consistency breaks down when I need to refer to the Passive House Institute U.S. or feel the need to quote some U.S. authors. Some contributors to GBA continue to insist on referring to Passivhaus buildings as passive houses, muddying the waters.

The British got this one right.

Jul 24, 2010 6:27 AM ET

by Brian O' Hanlon

I'm going to be plain awkward on this one I'm afraid. I live in Ireland, and we came very close to becoming German speaking back in the mid 20th century. I just can't bring myself to do it, I tell ya. I just can't bring myself to do it. Using the term 'passive house' suits me just fine.

But Mike's argument is perfectly logical.

Jul 24, 2010 7:32 AM ET

Response to Brian
by Martin Holladay

So how to you propose to handle the resulting confusion? Here in the U.S., tens of thousands of homes were built in the 1970s, 1980s, and 1990s following passive solar principles -- and none of these homes meet the Passivhaus standard. I call such a home a "passive solar house" but I have heard others call them "passive houses." Hence the confusion and the need for a system to distinguish between the two types of houses.

Jul 24, 2010 8:30 AM ET

by Interested Onlooker

The term redundancy is a well-understood carry-over from systems engineering. Redundant systems provide protection when the principal system fails to do what it's supposed to - exactly the way in which the term is being used here. The notion of using the word 'reserve' is questionable - a reserve is more of the same which is not deployed until required. Like adding another battalion of disposable infantry or a coat of paint.

A redundant system is not a reserve - it is a complete replacement. And yes, it is superfluous, until the primary system fails - which it will. Failure mode analysis is something the building industry is not very good at and its products tend to fail rather often and rather messily. If a system (building, whatever) is going to fail (which it will) then it should fail partially, obviously and in a manner which can be corrected without wholesale dismantling of the system. A blocked toilet is a good example of this. Failure of a WRB, backed by OSB and fiberglass batt is a really, really bad (but fortunately rare) example.

Jul 24, 2010 10:46 AM ET

Resulting Confusion
by Brian O' Hanlon

Yeah, I know Martin. I am not able to defend my position, and will not try.

The trouble with the Passivhaus for me really is, the amount of the iceberg underneath the waves, versus the amount visible above water. In the real world, the vast majority of building stock is the portion of the iceberg beneath the waves. Many close colleagues of mine are Passivhaus designers. I count myself very lucky to have the benefit of their knowledge and skills offered to me, on many an occasion. However, our conversations hardly ever lead up to talk about 'deep retrofitting', and the excellent work done in that huge field. Be it working on heating systems to make them better, or improving the airtightness of existing buildings through basic work, such as replacing old, single glazed leaky windows.

No, when I talk to my pals who are Passivhaus designers, our discussion always revolves around some new cutting edge project, recently completed by them. All of the housing stock (the iceberg underneath the wave) doesn't seem to bother them. The message is not getting through yet, to mister and missus Joe Six-pack, about their leaky single glazed windows. Mister and missus Joe Six-pack, receive all kinds of subsidy and support from central government, which is duly sent out through the cracks again, in high gas fuel and electricity heating bills. I would like to give the Passivhaus movement the respect that it most definitely deserves, for setting a high standard. But the situation across the entire range of building stock is so bad - morally speaking, I cannot endorse the glory of one regiment of super-Panzer mark IV's. When the bulk of the army is still of foot, and probably bedded down in the trenches. When we have a more even distribution of quality in our housing stock, then I will give due recognition to Passivhaus's efforts. Many people will disagree with my position, I know.

Jul 24, 2010 11:08 AM ET

Basic Energy Improvements
by Brian O' Hanlon

I'll copy this comment over from the Q&A, How thick a SIP should I use? Just for the sake of information about energy retrofit policy in Europe. And to highlight the problems that exist in the larger part of the iceberg, that is our national building stock.

-40 F = -40 C
-30 F = -34 C
-20 F = -29 C
-10 F = -23 C
0 F = -18 C
10 F = -12 C
20 F = -7 C
30 F = -1 C
40 F = 4 C
50 F = 10 C
60 F = 16 C
70 F = 21 C

Okay, I think I have a handle on this Fahrenheit business now. Anything below 30 F in Ireland is considered a show stopper. The entire country simply grinds to a halt, and no body leaves their homes. Well that is an exaggeration - but surfice to say, we aren't set up to deal with cold conditions. That is why our building standards and codes were always so easy to meet.

Anything above 70 F, is considered overheating of the living space during the heating season, and a waste of energy in our 'Building Energy Rating' software. Somewhere between 60 and 70 F, is considered okay for the non-living area zones during the home-occupied hours of the heating season. If you can tolerate below 70F in your living room, well and good.

But the trouble with many of our homes here in the British Isles, is that they are currently over-heating to an excessive amount, and thus burning through too much fuel. That is what our energy rating scheme was designed to fix. Though the tax credits and such, have not been set up in anything like the way they do in north America. We still rely on fairly inefficient grant systems to try and stimulate a retro-fitting industry here. There are grants to install room and WH thermostats etc.

Jul 25, 2010 10:44 PM ET

by mike

I have tried to be consistent and refer to Passivhaus buildings using the German spelling. It is a courtesy to readers.

and i thank you for it!

i just refer to them as PHIUS on my blog and with correspondences...

after working/living abroad so long, i prefer zuerich or zürich to zurich, koeln or köln to cologne, etc.

Jul 26, 2010 11:12 AM ET

by the way
by j chesnut

Please note my legal and given full name is J Chesnut; not J. Chestnut.
; )

Jul 26, 2010 11:41 AM ET

Response to J. Chesnut
by Martin Holladay

J. Chesnut,
Correction noted, although I suspect you posted your comment on the wrong page.

Jul 27, 2010 4:45 PM ET

by the way J not J.
by John Brooks

I think he is also trying to tell you that his first name is "J" not "J."

Jul 29, 2010 3:37 PM ET

Passive House
by Greg Duncan

The correct spelling in the United States is Passive House, not Passivhaus. The concept of super-insulated passive solar buildings started in the United States and English-speaking parts of Canada. Dr. Wolfgang Feist, the head of the Passivhaus Institut, uses the term Passive House when writing in English. If we adopt the German spelling of "Passive House", should we also adopt the German spelling of the word "institute"? And instead of "car" let's call it a "PKW" -- less ambiguous and reflects the German origins of the automobile. You get my point. Anyway, the official certifying agency for Passive Houses is the Passive House Institute US, which uses the English spelling.

Jul 29, 2010 3:49 PM ET

Response to Greg Duncan
by Martin Holladay

The chief responsibility of a journalist (or any writer) is to serve the reader. The entire country of Great Britain, and at least half of all journalists writing in the U.S., agree on the importance of distinguishing between the passive solar houses that have been built here for decades and recently built houses that have met the Passivhaus standard established by Dr. Feist in Darmstadt.

The "Passivhaus" spelling is respectful of the standard's origin and serves a vital purpose -- avoiding confusion. It establishes a distinction that the use of the phrase "passive house" fails to make.

Jul 30, 2010 12:50 AM ET

Passive House
by Greg Duncan


I hope you didn't see my comment as a criticism of your use of the word "Passivhaus". Your audience is international and it makes sense that your word choice reflects that. My point is that the capitalized term "Passive House" is the correct designation for a building certified by the Passive House Institute US and that PHIUS has logical reasons for using this English spelling.

Moving on, I totally agree with the preferred terms "vegetated roof" and "ground-source heat pump". Those are much clearer than "green roof" and "geo-thermal heat pump".

Aug 1, 2010 5:34 PM ET

Clarification Sought
by Interested Onlooker

"the capitalized term "Passive House" is the correct designation for a building certified by the Passive House Institute US and that PHIUS has logical reasons for using this English spelling."

Does the Passive House Institute US decree that its acronym be pronounced fie-us, pious or in some other way?

Dec 15, 2010 10:31 PM ET

Edited Dec 15, 2010 10:34 PM ET.

An Adjective Phrase, Not a Modified Verb
by Riversong

As a stickler for clear and accurate language, I think the common usage of "dense pack cellulose" is fine, as it is meant to differentiate itself from attic "loose fill cellulose" (not loose filled).

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