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Belgian Passivhaus is Rendered Uninhabitable by Bad Indoor Air

Inward solar vapor drive and damp earth tubes conspire to ruin an expensive new superinsulated home

Posted on Jun 1 2012 by Martin Holladay

The first single-family Passivhaus in the U.S. was completed by Katrin Klingenberg in 2004. Klingenberg’s superinsulated home in Urbana, Illinois includes two unusual features: a ventilation system that pulls fresh outdoor air through a buried earth tubeVentilation air intake tube, usually measuring 8 or more inches in diameter and buried 5 or more feet below grade. Earth tubes take advantage of relatively constant subterranean temperatures to pre-heat air in winter and pre-cool it in summer. In humid climates, some earth tubes develop significant amounts of condensation during the summer, potentially contributing to indoor air quality problems., and walls that include an interior layer of OSB. These details were not invented by Klingenberg; she adopted practices that were commonly used by European Passivhaus builders.

Although many North American designers have copied Klingenberg’s details, earth tubes are beginning to fall out of favor. Yet even in 2012, earth tubes are still being promoted by some Passivhaus builders.

By December 2007, when I first interviewed Dr. Wolfgang Feist, the director of the Passivhaus Institut, Feist was no longer recommending earth tubes. When I asked Feist whether earth tubes in Europe had experienced problems with condensation and mold, he answered, “There were problems in northern Europe, especially in Scandinavia. In Central Europe we haven’t had any hygienic problems so far. Actually, I’m not sure why we don’t have these problems in Central Europe. But I don’t advertise these systems any more, mainly because they are too expensive.”

The classic European wall

European Passivhaus builders (and Klingenberg) favor the use of a superinsulated wall system with three distinguishing characteristics:

  • Vapor-permeable exterior sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. made of fiberboard.
  • Thick insulation — usually cellulose or blown-in fiberglass rather than spray foam or rigid foam.
  • A layer of OSB on the interior side of the wall to act as an air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both. and vapor retarder.

Many American Passivhaus proponents (including Albert Rooks of Small Planet Workshop) endorse this type of wall assembly. They often claim that such a wall assembly is a better choice than one with thick exterior foam, arguing that it’s best to use vapor-permeable exterior sheathing so that a wall can dry to the exterior.

A case study in Belgium

Homes with earth tubes and vapor-permeable exterior sheathing can perform well — but only if the designer uses a whole-building approach that considers moisture movement from all angles. Moreover, if a builder makes installation errors, all bets are off.

A recent case study of a house in Belgium highlights the importance of getting these details right. The home's problems were discussed in an academic paper by Dr. Hugo Hens, a professor in the Building Physics unit of the Department of Civil Engineering at the University of Leuven in Belgium. His paper, “Passive Houses: What May Happen When Energy Efficiency Becomes the Only Paradigm,” was presented at the 2012 ASHRAEAmerican Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). International organization dedicated to the advancement of heating, ventilation, air conditioning, and refrigeration through research, standards writing, publishing, and continuing education. Membership is open to anyone in the HVAC&R field; the organization has about 50,000 members. Winter Conference in Chicago. (I'd like to credit Richard Kadulski, the editor of Solplan Review, for alerting me to Hens’s paper.)

The Belgian house was designed to meet the Passivhaus standard. Here are some facts about the house:

  • Completion date: December 2005.
  • Area: 2,034 square feet (1,561 sq. ft. of treated floor area using the PHPP definition).
  • Number of stories: 2 stories plus an unoccupied conditioned attic.
  • Foundation: Slab on grade.
  • Foundation insulation: 7 inches of foam (R-36).
  • Wall construction: Wood framing.
  • Wall details, inside to outside: drywall, OSB vapor retarder/air barrier, 12 inches of cellulose insulationThermal insulation made from recycled newspaper or other wastepaper; often treated with borates for fire and insect protection. (R-43), vapor-permeable wood fiberboard exterior sheathing, 1 inch air space, brick veneer. (The type of fiberboard sheathing used in Europe is impregnated with wax; like Zip System sheathing, it is considered a WRB if the seams are taped, so no housewrap or asphalt felt is required.)
  • Roof assembly: Insulated sloped roof with 12-inches of cellulose (R-43).
  • Windows: Triple-glazed low-eLow-emissivity coating. Very thin metallic coating on glass or plastic window glazing that permits most of the sun’s short-wave (light) radiation to enter, while blocking up to 90% of the long-wave (heat) radiation. Low-e coatings boost a window’s R-value and reduce its U-factor. windows with argonInert (chemically stable) gas, which, because of its low thermal conductivity, is often used as gas fill between the panes of energy-efficient windows. gas fill.
  • Space heating system: Air-to-water 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. with electric resistance backup.
  • Space heat distribution system: Hydronic coil in the ventilation supply duct.
  • Mechanical ventilation: HRV(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. with fresh air intake drawn through a buried earth tube.
  • Air leakage rate: 0.68 ach50.

Something is terribly wrong

The homeowners (a family of five) moved into their new home in December 2005. Hens wrote, “Shortly after moving into the just-finished dwelling, the first complaints surfaced about degrading health with [these] main symptoms: coughing, shortness of breath, headache, dry throat, pain and weakness in the legs, painful muscles, fever, diarrhea, paleness, nausea, tiredness and a loss of taste. Also, visitors staying in the dwelling for a couple of days developed analogous symptoms. The complaints were confirmed by a medical diagnosis of [the] parents and children at a university hospital.”

The family complained that the house was uncomfortable, with “very high relative humidity indoors. … They mentioned too low room temperatures in winter and unpleasant high living room temperatures in summer. … The inhabitants confirmed they were forced to open the two windows in the attic space to keep the indoor environment ‘habitable.’ ”

Several problems were discovered, including the following:

  • The air space between the brick veneer and the wall sheathing was not ventilated at the top and bottom of the wall.
  • The insulation contractor left insulation voids at the top of the exterior walls.
  • There was standing water in the earth tube.
  • The OSB installed on the interior walls was damp.
  • The HRV air flow was less than the design specifications.

Inward solar vapor drive

As builders in the U.S. have known for many years, the combination of a so-called “reservoir” claddingMaterials used on the roof and walls to enclose a house, providing protection against weather. like brick veneer and a vapor-permeable sheathing like fiberboard is extremely risky. Hens noted, “During warmer weather after a rainy period, part of the moisture [absorbed by the brick veneer] diffuses across the inside leaf to the inside where it humidifies the OSB, a phenomenon called solar-driven vapor flow. ... In fact, temperature at the cavity side of a wet west … [or] south looking brick veneer wall may pass 35°C (95°F) during warm summer days, giving water vapor saturation pressures up to 5260 Pa (109.5 lbf/ft²), high enough to create an additional daily vapor flow to the inside, which further increases humidification of the OSB. Solar-driven vapor flow may thus have activated global aldehyde release by the OSB during the summer months. … Solar-driven vapor flow is not considered by most of the designers and builders.”

Hens concluded that “high relative humidity, in combination with quite high summer temperatures indoors, must have boosted formaldehydeChemical found in many building products; most binders used for manufactured wood products are formaldehyde compounds. Reclassified by the United Nations International Agency for Research on Cancer (IARC) in 2004 as a “known human carcinogen." emission by the oriented strand board sheathing.” The concentration of formaldehyde in the indoor air was measured at 43.4 to 70 µg/m3 (35 ppb to 57 ppb). According to Hens, “the formaldehyde concentration is much higher than allowed in most countries.”

This same phenomenon — inward solar vapor drive from brick veneer through vapor-permeable sheathing — caused a disastrous cluster of building failures in Cincinnati, Ohio. The Ohio problems began surfacing in July 1999. Hundreds of homes suffered wall rot, and the enormous repair costs drove the developer, Zaring Homes, into bankruptcy.

If only Zaring Homes had specified rigid foam sheathing instead of fiberboard sheathing, these walls would have been fine.

You call that fresh air?

As it turned out, the earth tubes installed at the Belgian house were a big mistake. Hens wrote, “The search for causes [of the IAQIndoor air quality. Healthfulness of an interior environment; IAQ is affected by such factors as moisture and mold, emissions of volatile organic compounds from paints and finishes, formaldehyde emissions from cabinets, and ventilation effectiveness. problems] started with a camera inspection of the overall ventilation system. … [The camera] revealed the presence of stagnant water and construction dust in the supply ducts." According to Hens, the source of the water was rainwater intrusion.

Hens continued, "In 2006, the contractor renewed [repaired] the ground pipe, however without success. Again, it collected water. A second renewal in 2007 brought some upgrade; however, still, the ground pipe did not remain dry. In fact, in summer, relative humidity in the pipe passed 80% during prolonged periods of time, creating favorable conditions for mold to germinate on the pipe walls.”

IAQ testing “revealed the presence of spores of penicilium, aspergillus fumigatus, aspergillus versicolor and aspergillus niger.” Hens noted, “High relative humidity in the supply air leaving the ground pipe also caused humidification of the filter at the supply side of the heat recovery unit, turning it into a preferred medium for mold to germinate and sporulate. That most probably explained the presence of aspergillus spores in the indoor air.”

Hens concluded, “Ground pipes are potentially a risky technology. Though solely promoted as energy savers, their impact on energy consumed is too minimal [for] the possible risk they create in terms of degrading supply air quality.”

The ventilation rate was low

According to Hens, the air flow delivered by home’s mechanical ventilation system was less than the design specification. (Considering the fact that there was standing water in the fresh air supply duct, it’s hard to know whether this was a problem or a blessing in disguise.)

The designer called for 182 cfm of ventilation. By U.S. standards, this was a very high ventilation rate. (According to the ASHRAE 62.2A standard for residential mechanical ventilation systems established by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. Among other requirements, the standard requires a home to have a mechanical ventilation system capable of ventilating at a rate of 1 cfm for every 100 square feet of occupiable space plus 7.5 cfm per occupant. formula used in the U.S., the home should have been ventilated at a rate of 53 cfm.) The supply air flow was measured with the HRV operating at high speed; it was only 62 cfm. Although this air flow rate exceeds the ventilation rate stipulated by ASHRAE 62.2, it was less than the rate called for in the construction documents — indicating (according to Hens) that the ventilation system was never commissioned properly.

Local authorities conclude: it’s uninhabitable

Less than two years after the family moved into their new home, the house was declared uninhabitable. “Indoor environmental quality … was so health-threatening that the passive dwelling was declared ‘uninhabitable’ by the communal authority in 2008. After the family left the house, the health complaints mentioned above disappeared.”

Since the home was vacated, contractors have been working to correct the building’s flaws. I haven’t been able to learn any details about the ongoing corrective work. Lawyers are now involved; according to Hens, it is now “a court case which demands correct privacy.”

What are the lessons?

Hugo Hens’s case study is certainly valuable, but it’s hard to draw firm conclusions about what went wrong without knowing all of the facts. It would be interesting to know, for example, whether the buried earth tube was sloped to a sump. Here’s my guess: no, it wasn’t.

Even with imperfect knowledge, I’m willing to stick my neck out and offer my own conclusions:

  • If earth tube ventilation systems are well designed, properly installed, and regularly inspected, they can perform well. However, earth tubes are expensive to install, provide limited energy savings, and incur a significant risk of developing moisture and mold problems.
  • Most walls with vapor-permeable exterior sheathing and interior OSB perform well. However, it’s probably not a good idea to specify OSB with formaldehyde on the interior side of your walls.
  • Vapor-permeable exterior sheathing does nothing to slow inward solar vapor drive. If you plan to install a “reservoir” cladding like brick veneer, it’s safer to use rigid foam sheathing than a vapor-permeable sheathing like fiberboard.
  • Homes with high-R walls and low air-leakage rates are vulnerable to a variety of problems if details aren’t well thought out or if contractors are sloppy.

Last week’s blog: “Window-Mounted Air Conditioners Save Energy.”

Click here to follow Martin Holladay on Twitter.

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Image Credits:

  1. Hugo Hens
  2. Martin Holladay

Jun 1, 2012 10:15 AM ET

Edited Jun 1, 2012 10:26 AM ET.

Good Discussion
by albert rooks


What a catastrophe. I'm glad that you brought this up. We need to have this discussion.

While I can't say anything about the earth tubes since it's out of my area of knowledge, I do feel strongly about permeable assemblies - in the right climate.

I wish we had the details for the rainscreen. This is a real stumbling block here in the US. When we talk about a rainscreen gap, to us 1/2" is a "big one". When you consider the major function in this case of the gap is to vent the driven moisture out of the cavity so it's not driven into the wall. For that reason we recommend a minimum gap of 3/4" with clear vent channels top and bottom. It's still worthy to note that the standard gap used on these applications is 40mm, or 1-5/8". We recommend this, but it's such a leap here to do that on a wall most builders and passive house designers balk at it.

Here we can see a failure of two systems (we think). Bad things happen on all continents.

I don't agree that our methods and habits of exterior foam is the right course. I think it's the wrong course. We've got a lot of "smarts" here in the US who have built permeable assemblies over the years successfully. Doug McEvers is one of them.

When East meets West and we try new things, we are going to have some failures. I'm very dedicated to seeing this through and pushing permeable assemblies here in the US -with the right details. They have a lot to offer. So far we are only talking about firbeboard as sheathing, the next step is low density fibre board that is a high perm sheathing and a thermal break.

Wood is good and these wood based permeable assemblies correctly built (like anything else) will last generations. However, we have no right to skimp on the details and do it wrong. No mater if it's wood, foam or putting away a wet camping tent, moisture is pretty unforgiving.

Btw... Martin. This type of assembly is not unique to passive house. It's the most widely used central european bu ild: OSB on the inside and high perm outside. (Floris K, please feel free to dis-agree if you do, but it sure is what I see most on a wall, but not roof).

Jun 1, 2012 10:23 AM ET

Response to Albert Rooks
by Martin Holladay

You're right that vapor-permeable sheathing is common in Europe.

As I've written many times, back in the 1970s, everyone worried about wintertime vapor diffusion from the interior to the exterior; that's why so many builders used to install interior polyethylene. In a way, the use of interior OSB follows a similar philosophy -- the idea being that OSB is a vapor retarder, and that's a good thing on the interior of the wall. (Fortunately, the permeance of OSB is variable, so it's able to act as a smart vapor retarder to some extent.)

Here's the problem with the old 1970s theory, however: there really aren't any diffusion-related disasters due to diffusion of interior moisture outward. On the other hand, there are an increasing number of diffusion-related disasters due to diffusion of exterior moisture inward.

During the summer, vapor-permeable exterior sheathing isn't such a good idea -- especially if you have brick or stucco cladding. That's why rigid exterior foam performs so well behind brick or stucco.

Jun 1, 2012 12:18 PM ET

Is the "Euro-Wall" really the problem ?
by John Brooks

Most of the European walls and roofs that I have observed while websurfing seem to have claddings that are well ventilated.
I think this project may have many issues.

Did the "University Doctors" determine if the health threat was from the OSB off-gasing or from the Mold Spores?

Zero Roof Overhang and The Unshaded Summer Glazing probably didn't help.

Unshaded (high SHGC) glazing overheats living area in summer... OSB and (& plastic toys) cook.
It's warmer inside than outside (UninHabitable)
Air inside becomes less dense (more buoyant) than outside air
Occupants open attic windows...(a path)
The Atmosphere pushes uber air thru the 80% RH Earth Tubes (and mold factory filter).

Jun 1, 2012 12:28 PM ET

Edited Jun 1, 2012 12:30 PM ET.

Response to John Brooks
by Martin Holladay

The "Euro Wall" can certainly work if it is well detailed; however, as I noted in my concluding bullet list, I certainly wouldn't use vapor-permeable sheathing behind brick veneer.

As I noted in my article, many errors contributed to this failure. The fact that the air gap between the brick veneer and the sheathing wasn't ventilated certainly contributed to the problem. (However, it's worth noting that in the U.S., the weep holes at the base of brick veneer walls are often too small to provide an adequate inlet for ventilating air, and many brick veneer installations lack venting at the top.)

And I'm sure you know that it's very difficult for physicians to pinpoint the cause of symptoms like those of the Belgian family discussed in this article. The air in their home had a great many problems, ranging from high humidity to high formaldehyde levels to the presence of mold spores. Suffice it to say that the air was unhealthy.

Finally, you're right that opening second-floor windows could have increased the rate of air flow through the damp earth tubes.

Jun 1, 2012 2:23 PM ET

Foam sheathing
by Doug McEvers

In the late 1980's I built a house in the Twin Cities that had 2x6 walls specified and was to be brick on the front and the rest stucco. In my move to make the house more efficient I insisted we use foam exterior sheathing to increase the wall R-value. The stucco contractor installed felt and metal lath, then did the typical 2 coat stucco. This house performed well and adding the foam sheathing probably saved me a big headache. It has been my policy when using a single 2x6 wall to add foam sheathing to increase performance, every once in a while things work out.

This was before the discovery of interior polyethylene, exterior OSB and the disaster with stucco and brick cladding. In a cold, dry climate I do prefer a double wall with a high perm sheathing and rainscreen, sometimes space does not allow it.

Jun 1, 2012 3:58 PM ET

Related Article
by John Brooks

Another Article related to Inward Solar Vapor Drive

Jun 1, 2012 4:12 PM ET

Response to John Brooks
by Martin Holladay

Thanks for the link. Here's a quote from Joe Lstiburek's podcast:

"So it rains on the brick, the brick gets wet, there is a lot of water stored on the surfaces of the brick. It is not drained because it is stored. It is like a sponge: You fill up the sponge with water, and then, once the sponge is filled, only then if you add more water does water drain out. In other words, if you add water to a brick wall, water doesn’t come out of the bottom; it keeps building up until you can’t store any more water, and then the water drains out. The reservoir is charged. Think of this as a water source.

"Next, the sun comes out and beats down on the brick. What happens to the temperature of the water in the brick when the sun beats down on it? It gets higher. Now there is hot water on the outside of the wall. So moisture flow is going to go from where? Warm to cold. Think of the water as splitting—some of it is going to evaporate to the outside, and some of it is going to evaporate to the inside. The concentration of water in the brick is greater than the concentration of water in the outside air but also the water in the air behind the brick. Moisture is going to go from a higher concentration to a lower concentration."

Jun 1, 2012 4:45 PM ET

John, I think I see external
by mike eliason

John, I think I see external shades tucked behind the brick, though it's hard to tell from the photos.

Wow. Thoroughly disgusting. Did the article state if the pipes were plastic v. concrete? Was the system designed to drain? Doesn't sound like it.

Two things stand out...
One - 0.68ACH50, paired with insulation voids leads me to believe there were some large quality control issues on site. Construction dust in the ducts would seem to reinforce that.

Two - I've never seen this wall assembly paired w/ a brick fassade. And I read and/or own waaaay too many EU technical manuals.

In Hens previously published papers - it seems his nomenclature when describing PH projects has evolved from 'additional insulation' to 'extreme insulation'. In a fairly recent article, he seemingly slams balanced ventilation because during a blackout, you can't open the windows or else intruders will get in. This seems a rather odd statement to me, as the tilt/turn window allows just that (ventilation without intruders), and is commonplace throughout the EU.

Jun 1, 2012 5:00 PM ET

Wow. This is a juicy one,
by John Semmelhack

Wow. This is a juicy one, Martin!

First, a small point - if the air leakage rate you mentioned is correct (0.68 ACH50), then this can’t be a Passivhaus. A Passivhaus would have to be just a little bit tighter.

Next - to my knowledge, earth tubes have never held much favor with North American designers (Passive House designers or otherwise). Specifically regarding Passive House practitioners in North America - in PHIUS’ trainings going back to at least 2009 (PHIUS only started training consultants in 2008) earth tubes were and have since been presented as “risky” and were only to be attempted on consultants‘ own houses, if they felt like taking a chance.

Finally, linking this case with the Zaring Homes debacle is going too far. While it’s always good to remember when and why our buildings fail, the Zaring wall assemblies had three big differences to the Belgian assembly: 1) The Zaring brick was coupled to the fiberboard sheathing. No air gap. 2) The Zaring walls had an interior polyethylene vapor barrier. 3) The Zaring homes were cooled in the summer. 1+2+3 = building failure in lots of climates.

Jun 1, 2012 5:14 PM ET

Edited Jun 8, 2012 9:48 AM ET.

Response to John Semmelhack
by Martin Holladay

Of course their are differences between the Zaring Homes failures and this Belgian failure. Nevertheless, there were major similarities, including brick veneer, vapor-permeable sheathing, and enough inward solar vapor drive to contribute to serious problems leading to the abandonment of the affected homes.

Many North American Passivhaus builders are enamored of earth tubes. Among the Passivhaus projects that have included earth tubes are:

1. Katrin Klingenberg's house (also known as the Smith house);

2. The Waldsee Biohaus in Bemidji, Minn.;

3. Chad Ludeman’s passive house project in Philadelphia;

4. A passive house in Toronto; and

5. Jason Morosko’s passive house in Ohio.

Below are two photos of earth tubes. The top photo shows the earth tubes at Jason Morosko's house, while the bottom photo shows the earth tubes being installed at the Waldsee Biohaus.

If you want to enlarge one of the photos, just click on it.

Jason Morosko - earth tubes 2.jpg BioHaus - earth tubes 4.JPG

Jun 1, 2012 10:35 PM ET

Edited Jun 1, 2012 11:23 PM ET.

I'm not overly sensitive
by albert rooks

John & Mike,

This isn't an indictment of Passive House. It just one of many building failures. This one just happens to be a Passive House project.

We need to talk about failures in an open conversation. They happen no matter what the design goals are. The future is in High R envelops. No question. As such, we all benefit from a healthy debate and maintain that "fear of failure" in ourselves and the building culture.

To that end, Martin, I'll throw out a couple of points of discussion:

Btw... I'm in the Pacific Northwest. Brick facade is a minority, so I'm leaving that point with your or others experience.

You wrote: "Many American Passivhaus proponents (including Albert Rooks of Small Planet Workshop) endorse this type of wall assembly. They often claim that such a wall performs better than a wall with thick exterior foam, arguing that it’s best to use vapor-permeable exterior sheathing so that a wall can dry to the exterior."

Thanks, I'm happy to be the "poster child" for drying to the exterior in cold climates. Even if I take some "bruises" over it. You wrote" They often claim that such a wall performs better than a wall with thick exterior foam" Maybe it didn't come out as you intended, or maybe I don't express it right, but both you and I know that from the narrow U Value (or factor) point of view: It does not matter if you arrive at that low conductivity by foam or fibre... It's still the same value. So it's not that it will perform better in a cold climate, it's that I think it's a better choice.

I don't want us to build millions of homes with 4" of exterior foam. Frankly, while it may thermally isolate the occupants and not cause health problems, consider that the average US home has around 2500 square feet of wall area. At 6" depth that is 1250 cubic feet of foam per average house. As High R value envelopes exponentially increase over the next 20 years and we get towards a million units... we get 1.25 billion cubic feet of foam. Like nuclear waste, it going to be with us for a while.

I think that's a crazy self destructive idea. I don't even feel the need to go further and explain why I feel that way. However... It's my judgement call based on my personal values, It's not that I'm saying that they perform better, I'm saying it's a more rational environmental choice.

I'm choosing to voice alternatives to wrapping everything in pretty blue, pink, or shiny foil faced foam, As you know, I'm a big fan (as you are too:) ) of exterior mineral wool. But... my personal favorite is wood.

We can build really good high R value assemblies that deal with cold sheathing by drying to the exterior. We can also screw them up just like the unfortunate collisions that come from an inch or two of exterior foam with a layer of Polly behind the drywall in a cold climate. You recall the Q&A case a week or two ago where the Q&A community were advising against a near disaster.

Jun 1, 2012 11:09 PM ET

Edited Jun 1, 2012 11:28 PM ET.

How about that Stucco?
by albert rooks


Just to lob a little challenge your way :)...

You wrote: "During the summer, vapor-permeable exterior sheathing isn't such a good idea -- especially if you have brick or stucco cladding. That's why rigid exterior foam performs so well behind brick or stucco."

The hard part for me to square with this is: The Swiss, Germans, and Austrians have had such great success with Permeable sheathing topped with stucco. It's the predominant exterior finish. Typically it's on masonry construction, but over the last 20 years, on high perm wood too.

As you know, I import woodfirbe boards from Agepan in Germany. You were there the day my first samples arrived in Olympia:) I've toured job sites, toured the woodfibre plant in Meppen, and I see that they have systems that call for a direct application. They have been doing this long enough that the building are working fine.

Attached is a picture that I took a few weeks ago in Hannover of a Passivhaus, in a 300 unit Passivhaus development in the center of town. I talked to the builder quit a bit. It was tough as his English was not good. The house in the pic with the vertical red detail is: drywall+service cavity+OSB+2x6 (or so) stud cavity+about 8" of high perm wood fibre at around R 3 per inch. Just like the Agepan THD that I stock and bravely promote. The exterior finish is stucco. Blow up the picture and look how big the field is between expansion joints.

I think they've got a system that works. While I don't have it down yet, I'm enough of a stubborn "woodhead" that I'm going to learn it.

It's still early in our small companies experience, so I'm pretty conservative in how we treat the high perm assemblies. As you can see, we have not put up any propaganda on the Agepan wood fibre on our website yet. We will only deal with a specific project, in a specific location until we are a little further down the road with it.

Okay... I guess the only challenge I threw out was to "challenge the limitations" of what some "think" can't be done with wood. Just because we can't today, doesn't mean that we can't tomorrow.

So where is Phillip Gross when you need him!?!

Image 8.jpg

Jun 2, 2012 5:39 AM ET

Edited Jun 2, 2012 7:49 AM ET.

Response to Albert Rooks
by Martin Holladay

First of all, thanks for being a good sport about my electing you to be the poster child for vapor-permeable exterior sheathing in the U.S. I'm well aware that my decision to elect you to that position is somewhat unfair.

Also, thanks for suggesting that it would be more accurate to report that you feel that vapor-permeable exterior sheathing "is a better choice" rather than "performs better." I have corrected the text of the article to reflect that point; I'm sorry if I was misrepresenting your position.

And yes, I remember standing with you outside of your garage in Washington as you opened the cardboard boxes containing samples of fiberboard sheathing shipped from Germany. If European-style fiberboard sheathing eventually becomes a common building product in the U.S., I'll be able to say that I was present at the birth of an industry.

Concerning building failures in general: I agree with you. While every building failure is a tragedy for the builder involved, it is an enormous opportunity and gift for the construction community in general. Builders should eagerly study failure stories; they are instructive. They help us all build better buildings.

Dramatic failures regularly occur in foam-sheathed buildings, of course, and also (apparently) in at least a few buildings sheathed with vapor-permeable sheathing. Each example of failure can provide a lesson.

You wrote, "I don't want us to build millions of homes with 4 inches of exterior foam. ... As high R-value envelopes exponentially increase over the next 20 years and we get towards a million units, we get 1.25 billion cubic feet of foam. Like nuclear waste, it going to be with us for a while."

Fair enough. But if your concern (and the concern of many builders who don't like exterior foam) is that foam is environmentally damaging, that doesn't mean we have to switch to vapor-permeable sheathing. We can also choose plywood, which might (for example) perform better than vapor-permeable sheathing behind brick and stucco.

Finally, you raise questions about the use of stucco over vapor-permeable sheathing in Europe. I'd love to know more about the details of these walls. Do European builders include a drainage gap between the stucco and the sheathing, for instance?

I know that in the U.S., tens of thousands of homes with stucco, OSB, and wood framing have experienced dramatic, expensive failures. I have reported extensively on these problems, both in Energy Design Update and in an article on GBA. According to many experts, inward solar vapor drive appears to be one element in these failures. That's enough of a concern that -- speaking personally -- I would never build a house with stucco siding over a wood-based sheathing unless the system included an air gap between the stucco and the sheathing.

Finally, here's a photo I took showing you with your newly delivered samples of vapor-permeable European fiberboard:

Albert Rooks - softwood fiberboard - 3.jpg

Jun 2, 2012 5:47 AM ET

Where did the water in the earth tube come from?
by Martin Holladay

This morning I just received an e-mail from Hugo Hens with an answer to my question about where the water in the earth tube came from. He wrote that the water in the earth tube was mainly due to the infiltration of rain water into the pipe, but that it is possible, even in "rainproof pipes, [that] relative humidity might touch such high values during late spring and summer that mold develops."

So -- it was liquid water intrusion. Obviously, the intake pipe did not drain to daylight; nor was there any provision for drainage on the house side of the system.

Jun 2, 2012 12:35 PM ET

Ventilation the key problem? / No VB in vapor perm. walls?
by Paul Price

Having more than one big problem does make sorting out the effects more difficult, and more difficult to draw conclusions. Obviously, in the Belgian case there are several problems especially the HRV with 'fresh' air from the earth tube and the bricks / poorly vented air gap / osb problems.

Surely the key causes are to due to inadequate ventilation design, both externally and internally, rather than in the use of vapor permeable insulation. Particularly if brick is used as a cladding, but ideally anytime, a very well ventilated air gap behind the cladding is essential, even with foam. Having a drainage plane moisture barrier (taped as an air barrier) to the outside of the fiberboard would also have been a good idea. As for the air from a mouldy earth tube, not good.

Do you think a vapor barrier in a thick, moisture-buffering (cellulose) wall/ wood fiberboard insulated wall is at all a good idea, especially in the non-extreme Belgian climate? How about getting rid of the OSB and using let-in 4x1 diagonal bracing for the racking. Then the wall is highly vapor permeable and breathes inward or outward depending on the season. Good ventilation on both sides takes care of the rest. There could be a vapor check to the inside, more as a second air barrier. Service cavity and breathable finish inside this.

Interested in how you think this plays and how resilient this build-up would be in different climates or with air conditioning?

Jun 2, 2012 2:16 PM ET

Edited Jun 2, 2012 2:43 PM ET.

Ah yes. what about that OSB?
by albert rooks

Martin wisely states:

"Even with imperfect knowledge, I’m willing to stick my neck out and offer my own conclusions: - Most walls with vapor-permeable exterior sheathing and interior OSB perform well. However, it’s probably not a good idea to specify OSB with formaldehyde on the interior side of your walls."

I'm not too concerned about our American OSB in this application. They do contain UF along with all of the other engineered wood products (TJI's LVS, etc). These products are exempt from the the current bans on UF.

However, we are not seeing the failures and toxicity even though we have plenty of opportunities to see them besides this interior OSB design.

The concern that the Belgium case has brought up is: Inward solar vapor drive that results in such high humidity that the inner OSB starts reacting and creating these high levels of toxicity. The case is put that the vapor drives through the high perm sheathing and onto the OSB. It's worse than normal because the OSB is on the inside of the air and vapor barrier (pressure boundary). There is no further check for it to infiltrate the inhabited space.


How is that different than an American code wall with a poorly vented reservoir material on the outside? In a code wall, you'd have the same drive hitting the OSB. The inner face of the OSB would off-gass into the stud bays and onto the imperfectly sealed drywall. The toxins would leak past the finish layer into the habitable space, just like it would leak through the smaller service cavity and past the imperfectly sealed finish layer in the diffusion open wall. In both of those cases the drywall is not the airbarrier.

To me it doesn't matter if the OSB is behind a 2.5" service cavity on the inside of a thick diffusion open wall, or on the outside of a 5.5" thick code wall. The point is to not create a situation where the drive wets the OSB. That is done by creating enough venting in the gap to accommodate venting the moisture drive. Theoretically you can place the brick veneer in the application provided the vent channel is big enough. However in practice, the vent channel requirement is not realistic to the realities of building, so no brick no matter whether the OSB is inside or outside.

I'd certainly rather not see any urea formaldehyde in the envelop at all. I was getting ready to check on the Belgium case study because I'm under the impression that these regions have regulated UF our of the products and they are now using PU. At least, the vendor I'm working sells it in Germany as a commodity. We should be demanding our mills to drop UF and supply us with non toxic materials.

When you wet OSB as much as the Belgium case, if it isn't the UF toxicity, it'll be the rot and mold that will make it uninhabitable. UF, or no UF, does not overcome improper layering.

Jun 2, 2012 3:22 PM ET

Vent the cladding
by K Willets

I'm not sure if the earth tube will add much humidity in the summer, given that RH already averages over 70 percent outdoors, and the temperature is close to indoor temperature.

I like to check the math on these things, so here goes:

If somehow the house is getting an additional 20% RH at 22C/70F, that's about 22 grains of water per pound of air according to a table I found. Assuming 100 cfm ventilation, that's

(.075 lbs/cf air weight)*(100 cfm ventilation)*(.000143 lb/grain)*(22 grains/cf vapor fraction)*24 hr*60 min. =33.97 lbs/day H20 added to the air. That's either a very leaky pipe, or the vapor is coming from somewhere else.

For the vapor drive issue, isn't venting the cladding the most immediate solution?

Jun 2, 2012 3:42 PM ET

Edited Jun 2, 2012 3:47 PM ET.

USB as a vapour barrier
by Colm O hAonghusa

Interesting thread this thus far.

I work with German made wood-fibre products here in Ireland and the general consensus now is that OSB, even 18 mm ( almost 3/4") thick graded as exposure class 1 cannot be relied on as a reliable vapour barrier. Tests have shown that even within the same batch there is a hugh variability in permeability levels.
If the budget will take it then I use an intelligent membrane over the inner face of the OSB, else use a more normal VB.
Unless the OSB is required for racking then 1/2' can be used which reduces the cost somewhat.

In the case under review, the lack of ventilation in the cavity behind the brick facing did'nt help.

What is not clear is if there were any fixings from the brick through the external sheathing to the timber frame.

Jun 2, 2012 4:35 PM ET

stucco over wood fiber
by mike eliason


In every holzfaser system i've seen, there is no gap for the stucco. they're all similar to this:

i think it's a separating layer/reinforcing mesh, followed by a 2 part, diffusion-open stucco system.

Jun 2, 2012 7:56 PM ET

Edited Jun 3, 2012 5:31 AM ET.

Response to Paul Price
by Martin Holladay

You wrote, "Surely the key causes are to due to inadequate ventilation design, both externally and internally, rather than in the use of vapor permeable insulation."

I don't think so -- at least concerning the lack of ventilation of the gap between the brick veneer and the exterior sheathing. After all, most U.S. brick veneer installations are very poorly ventilated, and yet most such installations don't result in failures due to inward solar vapor drive. That's because OSB and plywood are vapor retarders -- unlike fiberboard sheathing. Foam sheathing is better still.

You asked, "Do you think a vapor barrier in a thick, moisture-buffering (cellulose) wall/ wood fiberboard insulated wall is at all a good idea, especially in the non-extreme Belgian climate?" Vapor barriers are generally not problematic if they are integral with an insulation product that has a high enough R-value to keep the cold side of the insulation above the dew point. Vapor barriers are only a problem when they have no R-value. In other words, thick rigid foam won't cause problems, but polyethylene often does.

You are certainly right that the bad design and installation of the mechanical ventilation system (the HRV system) played a decisive role in this failure.

Jun 2, 2012 10:01 PM ET

Edited Jun 3, 2012 9:56 AM ET.

by aj builder, Upstate NY Zone 6a

Rooks and all

OSB is inexpensive and that is why it is used. But it when subjected to moisture can be the most expensive mistake in picking a sheathing material to utilize. It is not my favorite material.

Jun 3, 2012 12:18 AM ET

European Stucco
by steven konstantino

I believe they typically use a mineral silicate paint over stucco in Europe. This is a breathable, integrated weather barrier that lasts a long time. Maybe that helps. The homes in Albert Rooks photo also have decent roof overhangs. I would certainly call for a properly installed, vented rain screen no matter what.

Jun 3, 2012 4:29 AM ET

Response to Albert Rooks
by Martin Holladay

You wrote, "How is that [the Belgian case] different than an American code wall with a poorly vented reservoir material on the outside? In a code wall, you'd have the same drive hitting the OSB. The inner face of the OSB would off-gas into the stud bays and onto the imperfectly sealed drywall. "

There are two important differences:

1. In the U.S. case, there is an intervening layer of insulation -- ideally, 5.5 inches or more of cellulose (although more typically fiberglass) -- between the OSB and the interior drywall.

2. In the U.S. case, the damp OSB dries to the exterior. In the Belgian case, the OSB dried to the interior (meaning that evaporation was occurring -- including the evaporation of the formaldehyde -- on the interior side of the wall).

Jun 3, 2012 4:32 AM ET

Edited Jun 3, 2012 4:37 AM ET.

Response to Kendall Willets
by Martin Holladay

You wrote, "I'm not sure if the earth tube will add much humidity in the summer, given that RH already averages over 70 percent outdoors, and the temperature is close to indoor temperature. "

I haven't reviewed your math, but intuitively, it can't be a good idea to pull your fresh ventilation air through a duct with standing water in it.

You wrote, "For the vapor drive issue, isn't venting the cladding the most immediate solution?"

It would certainly help -- although job-site conditions often conspire to keep the weep holes at the base of brick veneer walls small. Moreover, masons often clog air gaps with mortar droppings, and masons have been known to screw up the ventilation at the top of a wall. These details require supervision and inspection, which adds cost to the job.

So, I'm not sure that ventilation is "the most immediate solution," since a layer of rigid foam is easier and (because it requires less supervision and inspection) probably cheaper.

Jun 3, 2012 4:42 AM ET

Response to Colm O hAonghusa
by Martin Holladay

You seem to be concerned about the fact that when OSB is used as an interior vapor "barrier" (I would probably use the phrase "vapor retarder" here), it doesn't stop the vapor well enough. You think that an additional product is needed to be sure that the OSB is better at resisting vapor flow.

But I don't think that there is any evidence that the house in Belgium needed a better INTERIOR vapor retarder. What this house needed was a better EXTERIOR vapor retarder.

Jun 3, 2012 4:47 AM ET

Response to Mike Eliason
by Martin Holladay

Thanks for the link to the photo.

To GBA readers who (like me) were momentarily puzzled by Mike's German vocabulary, "holzfaser" means wood fiber. Mike is referring to European systems that use stucco applied on top of vapor-permeable sheathing.

It's interesting that there is no gap. I wonder if any research labs have tested these systems for inward solar vapor drive.

Jun 3, 2012 4:50 AM ET

Response to Steven Konstantino
by Martin Holladay

It's possible that, as you suggest, the paint is protecting these European walls. But if your guess is correct, that means that failure of the paint could be enough to change the performance of the wall and put the wall at risk.

I certainly wouldn't want to select a wall system that depended on the integrity of a layer of exterior paint to keep moisture out of the wall.

Jun 3, 2012 7:15 AM ET

Edited Jun 3, 2012 7:15 AM ET.

OSB and European external render systems
by Colm O hAonghusa

The tests on the OSB to which I refer were to tape a a layer of a barrier on the inner face of the OSB and then apply the blower test with negative pressure. The layer bubbled as soon as there was a very small negative pressure. This to me is an air barrier failure.

This would suggest that in the case under review, the lack of air resistance on the inner face, ie the OSB meant that the solar vapor pressure build up had somewhere to go, line of least resistance so to speak.

The European renders on the external wood fibre materials, typically used in EWI projects, differ from a brick layer in so far as they dont have the mass or the specific heat capacity to heat up in such a concentrated way as brick. Neither do they aborb as much water in such a concentrated area.
They are, by design, water resistant but vapour permeable and work well in tandem with the natural materials used as insulation.

I cannot comment on the performance of foam/PU/PI/etc rigid insulation behind European type EWI renders. There is a lot of it being used in retro work for the housing stock in UK and Ireland but I think the jury is still out on the longer term performance issues

I cannot comment on the paint issue and its role in the EWI buildup, in any projects I have done the colour is in the render and no further painting is required. However it does point to the need to tell the home owner that if painting, it needs to be chosen carefully.

Micky mouse weep holes are never going to perform. Just consider the code requirements for ventilated eaves...

Jun 3, 2012 7:49 AM ET

Response to Colm O hAonghusa
by Martin Holladay

I was confused when you wrote (in your first post) that "OSB, even 18 mm ( almost 3/4") thick graded as exposure class 1 cannot be relied on as a reliable vapour barrier." The statement in your second post -- referring to "an air barrier failure" -- makes more sense. It sounds like the OSB needed better tape at the seams.

You wrote, "Mickey Mouse weep holes are never going to perform." Depending on your definition of "Mickey Mouse" -- not a technical term as far as I know -- I disagree. Properly detailed brick veneer installations can work well. The weep holes don't necessarily need to allow for significant ventilation -- although it wouldn't hurt, of course, if they did -- but they do need the following characteristics:

1. They need to be above grade.

2. They need to be integrated with durable flashing at the bottom of the air gap, and the flashing needs to be integrated with the WRB.

3. The flashing needs to extend to the exterior. In other words, the lip of the flashing should be visible below the weep holes.

4. The air gap above the weep holes must not be clogged with mortar.

Such systems work quite well -- especially if the brick veneer is installed on a building with exterior rigid foam sheathing.

Jun 3, 2012 8:28 PM ET

QAQC is critical to success
by Katrin Klingenberg

...with skillful design by a trained professional, a pre-certification design check and rigorous PH specialized onsite third party QAQC (such as in PHIUS+ RESNET QAQC) the problems that led to the downfall of the Belgian project would have all been caught during construction. Without rigorous quality assurance we might see failures of this kind here in the not too distant future also.

... 10 years later, the 8 projects in Urbana are doing exceptionally well, with and without earth tube! John is correct, we have never promoted earth tubes as PH solutions in NA, only for those who know how to handle them correctly. They can be an appropriate choice. All depends.

Jun 4, 2012 5:36 AM ET

Response to Katrin Klingnberg
by Martin Holladay

I agree with both your points. Clearly, the construction quality on this job in Belgium left a lot to be desired, and no one was looking over the builder's shoulder.

And it's good to hear that the homes in Urbana are doing well.

Jun 4, 2012 11:43 AM ET

Response to Martin re: Response to Colm O hAonghusa
by albert rooks


I'm pretty sure that Colm was describing a different test:

"The tests on the OSB to which I refer were to tape a a layer of a barrier on the inner face of the OSB and then apply the blower test with negative pressure. The layer bubbled as soon as there was a very small negative pressure."

Meaning that he was testing the OSB itself for air leakage. Place the AB at center of the OSB barrier, de-pressurize the envelop and watch for air passing through the OSB at panel center, not the taped seams.

This is not the first European builder that I've had discussions with that has tested the air leakage of OSB. It's seems like it becomes more common as builders work below 1 ACH50 as a matter of practice. -When you work on the "frontier" of building, you meet the darndest people...

Jun 4, 2012 11:52 AM ET

Edited Jun 4, 2012 11:53 AM ET.

Response to Albert Rooks
by Martin Holladay

If I understand the test correctly, there is an installed piece of OSB on the interior side of a wall. Let's assume that the OSB measures 4 feet by 8 feet. Then a builder tapes a piece of membrane to the center of the OSB; this membrane measures less than 4 feet by 8 feet. Let's assume it measures 2 feet by 3 feet.

After the membrane is taped in the center of the OSB, the house is depressurized. The builder observes a bubble of air that appears between the OSB and the membrane. Do I have it right?

If that's what's going on, why do you conclude that the air is leaking through the OSB? It seems far more likely to me that the air is leaking through the taped seams (that is, the tape used at the perimeter of the membrane).

Jun 4, 2012 12:13 PM ET

Edited Jun 4, 2012 12:18 PM ET.

Response to Martin Holladay
by albert rooks



"There are two important differences:
1. In the U.S. case, there is an intervening layer of insulation -- ideally, 5.5 inches or more of cellulose (although more typically fiberglass) -- between the OSB and the interior drywall.
2. In the U.S. case, the damp OSB dries to the exterior. In the Belgian case, the OSB dried to the interior (meaning that evaporation was occurring -- including the evaporation of the formaldehyde -- on the interior side of the wall)."

To try and be a little more detailed in my example:

1. In the U.S. case, there is an intervening layer of insulation -- ideally, 5.5 inches or more of cellulose (although more typically fiberglass) -- between the OSB and the interior drywall. [AR]: For my example, lets make it a code minimum wall which to me means it's probably a fiberglass batt (and not perfectly installed).

2. In the U.S. case, the damp OSB dries to the exterior. In the Belgian case, the OSB dried to the interior (meaning that evaporation was occurring -- including the evaporation of the formaldehyde -- on the interior side of the wall)." [AR in both cases the brick was not properly installed. That means that the US case cannot dry to the exterior. Solar Vapor Drive floods the system and it forces the same toxic behavior that can only seek balance to the interior. The batt insulation and drywall would not put up much resistance to the OSB drying and off-gassing to the habitable space, much like a lesser depth service cavity + drywall appears to have "passed gas" in Belgium.

I was only trying to suggest that the OSB's reaction to an improperly vented brick veneer would be similar regardless of it being "diffusion open to the exterior in Belgium", or an "American code wall in Minnesota". In both cases, the OSB is flooded with high humidity and must release the humidity, along with the toxins, to the interior as the system tries to balance itself.

My point was that in an extreme failure like this, the added 3" in cavity depth and batt insulation of the US wall would not be much resistance. The interior space would be equality uninhabitable.

The take away is that interior OSB is no more dangerous than exterior OSB to the effects of an unvented solar vapor drive.

Jun 4, 2012 12:29 PM ET

Edited Jun 4, 2012 12:31 PM ET.

Response to Martin Holladay
by albert rooks

OK, maybe it's me who is misunderstanding... - Not you!

You've got the test right as I was describing it. As far as the why's, I don't know. I've only heard about these tests and have never done one.

Now... I have to try it :)

I can take care of the edge issue by priming the tape with SIGA Dockskin. OSB + Dockskin + 1" of tape. That will create a perfect air seal. The remaining 1" of the 2" wide tape is on the membrane or poly. Darn I just missed a blower door test last week. I'll have to wait for the next project where we can replace a door with an OSB panel.

Jun 4, 2012 12:53 PM ET

Recently, Dr. Joe made this
by mike eliason

Recently, Dr. Joe made this statement regarding formaldehyde and ventilation rates...

"What’s amazing is formaldehyde in houses doesn’t respond to ventilation rate changes. So if you’re ventilating at 0.1 versus 0.2 versus 0.3, the formaldehyde concentration remains constant. The reason is the more you ventilate the more it emits. You ventilate less it emits less. Don’t put it in the building, that’s a phenomenally successful way of dealing with the problem."

So wouldn't this be an issue that's beyond whatever convoluted QAQC program anyone wishes to develop?

Regarding the leakiness of OSB - this came up on a couple of EU discussion boards lately, as well as a linkedin group. There was also a report titled, "Air Permeability Requirements for Air Barrier Materials in Passive Houses" that discussed the wide variability in leakiness through OSB. How's your Flemish?

I've seen some speculation that the EU OSB is leakier due to composition (less formaldehyde/more wax?) but I haven't seen anything remotely conclusive.

Jun 4, 2012 1:02 PM ET

Edited Sep 8, 2014 8:30 AM ET.

Response to Mike Eliason
by Martin Holladay

My Flemish is weak. My family lived in Holland for three years (1955-1958), but I since I was born in 1955, I don't really remember my time there ... or the Dutch I learned as a toddler.

There's always Google Translate: "[We] checked with manufacturers [who] taught us that some people claim that their [OSB] panels [are] airtight and they have never received any complaints regarding such a phenomenon. Others admit that their OSB panels are indeed not completely airtight."

[Later edit: Here is a link to the paper in English: "Air permeability requirements for air barrier materials in passive houses."]

Jun 4, 2012 1:17 PM ET

OSB inside vs. outside
by Douglas Horgan

In a summer vapor drive scenario, wouldn't exterior OSB be warm, nearly the temperature of the brick veneer (or the cavity air anyway)? Therefore well above the dew point?
OSB on the interior side of the insulation, on the other hand, will be much cooler, often below the dew point behind the solar-heated, rain-saturated veneer. (Particularly if air conditioning is in use.)
The one time I saw this in real life, the exterior OSB sheathing looked and measured dry, with no biological growth; but the interior drywall was saturated and moldy.

Also, Martin I think there would be no pressure difference between the back of the OSB and the plastic in this test scenario, so no reason for air to enter through the tape. For depressurizing the house to push the plastic toward the interior, there must be connections through the OSB to the outside.
While I haven't seen much about this issue in North America, I did hear about a house where the air leakage went up after the roofers nailed down the shingles. The contractor believes it was all the little holes!

Jun 4, 2012 2:15 PM ET

earth tubes and K Klingenberg
by Laura Blau

For the record. I took the PHIUS Passive House training summer of 2009 at Parsons in NYC and Katrin did not encourage eath tubes. She was quite clear that earth tubes were not appropriate for most US climates, and required maintenance similar to a "pet", her dry humor for discuraging their use.

Jun 4, 2012 2:28 PM ET

Response to Laura Blau
by Martin Holladay

I'm glad to hear that there is a general consensus on the fact that earth tubes are usually ill-advised. It's too bad that the Belgian designer and builder didn't get good advice before they finalized their plans.

Jun 4, 2012 2:45 PM ET

Response to Mike Eliason
by John Semmelhack


Regarding quality assurance and quality control - why would the elimination of urea-formaldehyde in certain materials be beyond the potential scope of a QAQC program (internal or 3rd-party)? It seems to me that eliminating the source of the problem would be something a project team would wish to assure.

Jun 6, 2012 4:42 PM ET

Unbuilt houses often work well
by Derek Roff

Martin said, "If only Zaring Homes had specified rigid foam sheathing instead of fiberboard sheathing, these walls would have been fine." It's easy to claim great performance in a house that was never built. This kind of "spec" housing always performs well. But in an article focused on real, as-built houses, and their problems, I think it out of place to offer such predictions of how a group of homes would have performed with one change. It's misleading at best to compare a possible design change of one wall-assembly element to complex in-the-field failures of the Belgian house. After all, just like your hypothetical modified Zaring Homes, the Belgian house performed perfectly, up until construction began.

I have a similar objection to the statement, "Vapor barriers are only a problem when they have no R-value." This is an overly broad assertion, to which many counter-examples have been described in actually built houses using foam. I'm not saying that foam was the sole source of the problems, just that having an R-value in your vapor barrier doesn't guarantee anything.

Jun 6, 2012 5:04 PM ET

Brick airgap with (now) unvented attic
by Josh Wimpey

Hi, I live in a 1953 house outside of Washington DC with exterior walls of the following construction and zero roof overhang:

fiberglass batts
drywall/plaster/wood paneling (depending on the room)

We recently insulated the roof with 3.5" of CC polyurethane spray foam because the attic had too many protrusions to seal tightly and the duct work is all exposed there as well. My concern is that by retrro-fitting an unvented attic, there is now no place for the brick-to-block-to-drywall cavity(s) to vent their moisture trappings to.

We have been monitoring the attic temp and humidity levels and have thus far seen nothing out of the ordinary but wonder if we should do some forced ventilation or dehumidification as a precautionary measure?

Jun 6, 2012 5:45 PM ET

Response to Martin comment #33
by Derek Roff

Martin said, "It seems far more likely to me that the air is leaking through the taped seams (that is, the tape used at the perimeter of the membrane)."

It seems to me that Martin's explanation means that air is leaking from the reduced pressure airspace in the room to the increased pressure airspace between the membrane and the OSB. Leaks in the tape could neither create nor maintain airflow from low pressure to high.

Jun 6, 2012 6:34 PM ET

Edited Jun 6, 2012 6:43 PM ET.

Response to Derek Roff's comments on Zaring Homes
by Martin Holladay

I'm not sure why you are scoffing at my suggested change to the sheathing that was used in the failed Zaring Homes. According to many building experts who looked into this disaster, the cause was clearly inward solar vapor drive from the damp bricks through the fiberboard sheathing that led to the moisture entering the wall cavity. Clearly the fiberboard sheathing was the weak link in the system. Of course, you could change other aspects of the wall assembly if you preferred -- for example, substituting vinyl siding for brick veneer would also have prevented problems.

The other sentence you object to -- "Vapor barriers are only a problem when they have no R-value" -- was stated in the context of a longer paragraph. If a vapor barrier has a high enough R-value to keep the cold side of the material above the dew point, you're not going to get condensation. As long as a wall assembly can dry in either direction from such a vapor barrier, the wall will perform well. This is in stark contrast to a vapor barrier like polyethylene, which has no R-value and can lead to all kinds of problems.

Jun 6, 2012 6:38 PM ET

Response to Josh Wimpey
by Martin Holladay

You don't have to worry about the performance of your wall assembly. Brick veneer over a concrete-masonry unit wall is a very robust system. Especially since you note that you "have seen nothing out of the ordinary," I don't think you have any reason to worry.

Jun 6, 2012 6:42 PM ET

Response to Derek Roff's comment about leaks through tape
by Martin Holladay

I'll admit that I don't know what's going on with the OSB air leakage test that Albert Rooks described. All I know is that I find it hard to imagine that much air leaks through the field of an OSB panel.

Jun 7, 2012 1:14 AM ET

Importance of vapor-permeability, Sydney Australia
by Meredith Trevallyn-Jones

A very informative post. Here in Sydney Australia we enjoy a warm temperate climate, build in brick-veneer and have only in the last few years started to require insulation in walls and, as a result, experience condensation problems.
Typical wall construction - inside to outside: drywall + 2x4 studs (now with 3 inches fibreglass batts) + building wrap + 2 inch cavity + brick veneer. The building wrap has typically been vapor impermeable but the emergence of winter condensation problems in houses built in the last few years has led to recommendations for permeable building wrap and the installation of impermeable membranes such as polythene or aluminium foil on the interior side.
Since Sydney has warm summers (warmer than LA) and summer rainstorms and air conditioning is the norm, I'm wondering if solar vapor drive could become a problem. I note that the first Passivhaus now being built in Auckland New Zealand - which has a similar climate to Sydney - is using a variable permeability air tightness system (Pro Clima Intello) at the interior. Does anyone have any experience with such products?
Thanks also for bringing up the issue of earth tubes. There has been some experimentation here with them but not enough discussion about the possible health issues.

Jun 7, 2012 12:19 PM ET

More information from Hugo Hens
by Martin Holladay

A few days ago, I sent an e-mail to Hugo Hens asking whether this wall assembly included a water-resistant barrier (WRB) like Tyvek or asphalt felt on the exterior side of the fiberboard sheathing.

The answer was surprising, to say the least: there is no WRB at all -- no membrane to address liquid water that gets past the brick veneer.

In other words, this house had a whole basket of problems.

Jun 7, 2012 7:08 PM ET

HRV intake
by Hobbit _

At the risk of getting completely buried under a long thread...
In various thinking about my own pending retrofit and HRV
installation, it's occurred to me that the fresh-air intake
of one that isn't an ERV should have a humidity sensor in the
stream, so that if it's about to shovel stupidly humid air into
the building it can either shut down, or go to a really
minimal flow rate -- something that the HVAC will be able
to easily deal with, rather than forcing it to handle extra
latent load. Once my system is installed I might experiment
with this. Such a rig might have saved the earth-tube situation,
or at least alerted someone that the air from them wasn't
acceptable to bring inside.
My system is also going to vent the cathedralized attic -- not
in an extreme way, but enough to matter. This seems to be
something that's completely ignored -- what happens in the attic
under a tight envelope if it's basically sealed off with no
air passage other than a few ceiling leaks??

[Editor's note: To continue reading comments, click on Page 2]

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