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Green Building News

Researchers Seek High-Performance Walls for Study

Wireless sensors will be installed in exterior walls to gather information on moisture and temperature

High-performance walls like this double-stud wall are the target of an upcoming research project that will include measurements of moisture content, relative humidity, and temperature. Volunteer builders are being sought.

Researchers are looking for builders willing to volunteer to take part in a field study that will measure moisture, temperature, and humidity inside high-performance walls in moderate and cold climates.

The Home Innovation Research Labs, a subsidiary of the National Association of Home Builders (NAHB), has put out a call for builders of new homes — additions and remodels aren’t included in the study — who would allow wireless sensors to be installed inside wall cavities. The sensors — as many as ten in a single building — will transmit the data to a remote server.

There are a couple of caveats: walls should have an R-value of at least 20, be relatively airtight, and be located in Climate Zone 4 or higher.

“The results of the study will provide real-life data on long-term performance of walls constructed using energy-efficient practices,” an announcement from the Research Labs said.

It doesn’t cost anything for a builder to participate, and neither builder names nor exact building locations will be included in the final report. Builders can submit multiple homes; monitors will go in this spring and summer with monitoring to continue for at least a year.

Program details and objectives

Research Labs will provide the sensors and related hardware, along with instructions for how to install them. Builders will be responsible for installation, discussing the project with homeowners, and supplying design and construction documentation, such as the results of blower-door testing.

Moisture accumulation in exterior walls is an area of intense interest to building scientists. As buildings become tighter and better insulated, the risk of for long-term moisture damage to sheathing and framing has gone up, particularly in regions with long, cold winters. The topic is the focus of research by public and private labs and has been addressed in many articles and Q&A threads at GBA.

Nay Shah, one of two directors of the project, said that moisture and temperature issues in milder climate zones are much better understood, but there are still plenty of unknowns about high-R walls in cold climates.

“Yes, this has been studied a lot by many people,” he said, “But we do believe there is lots to be learned.”

Of particular interest: what happens inside walls with vapor impermeable layers on both the outside and inside; how ZIP System walls with exterior insulation perform; and which type of rigid insulation applied to the outside of the building (extruded polystyrene, expanded polystyrene, or polyiso) works best.

The number of sensors will vary by the house, but typically would range from five to ten, he said, adding that it was important the sensing equipment be installed before drywall.

“We don’t want to tear into your walls,” he said.

Partial results should be available by next spring, with a full analysis completed by June 2017. Interested builders can apply online at this link.


  1. user-1041981 | | #1

    Why Only Foam
    The article says NAHB wants to research "which type of rigid insulation applied to the outside of the building (extruded polystyrene, expanded polystyrene, or polyiso) works best."

    Why only vapor-closed foam? What about mineral wool like "ComfortBoard IS"?

    (note: I used Zip Wall with ComfortBoard IS on the exterior for my house last year)

  2. GBA Editor
    Martin Holladay | | #2

    Response to C.B.
    I'm not involved in this research in any way -- but many researchers narrow their focus, because it's impossible to study all variables. If you limit the variables, you make the research easier to perform (and more affordable).

    Another issue: it would be hard to round up enough builders who have built homes with exterior mineral wool.

    Finally, few building scientists worry about moisture buildup in walls with exterior mineral wool, because these walls dry easily to the exterior.

  3. user-1041981 | | #3

    Response to Martin
    I agree with the concept of limiting the variables.

    The reason I mentioned what I did is that while "few building scientists worry about moisture buildup in walls with exterior mineral wool because these walls dry easily to the exterior", I'm not completely sure that is true with Zip System. Huber publishes the permeance (12 to 16 perms) of the WRB part of Zip, but I haven't seen them confirm the permeance of the full Zip board. How much moisture accumulates in the winter in Zones 5/6 which can't work through to the outside?

  4. GBA Editor
    Martin Holladay | | #4

    Response to C.B.
    The permeance of Huber Zip-R sheathing is less than 1 perm. No builder should install Zip-R sheathing under the misapprehension that this type of wall will dry to the exterior. No significant amount of drying will occur through the Zip-R sheathing, so these walls should be designed to dry to the interior.

    That means that anyone who purchases Zip-R sheathing should make sure that the R-value of the Zip-R sheathing meets the minimum thresholds set out in this article: Calculating the Minimum Thickness of Rigid Foam Sheathing.

  5. user-1041981 | | #5

    Response to Martin
    I agree with your comments about Zip-R.

    However, the product I was refering to was the standard Zip (without integrated insulation). Huber publishes the permeance of the WRB part of the Zip System (green or reddish colored adhered membrane) as 12-16 perms, but they do not publish the permeance of the complete Zip System sheet. I have attached a Huber document where the second-to-last sentence describes the permeance of the WRB-portion of the Zip System sheet, but it doesn't say the permeance of the complete WRB+OSB Zip System sheet.

  6. GBA Editor
    Martin Holladay | | #6

    Response to C.B.
    Regular Zip sheathing has a permeance of between 2 and 3 perms. I don't know where I first learned that fact (which I have recorded in a permeance table I maintain); I learned it either from the technical team at Huber, or from building scientist John Straube.

  7. christopherw | | #7

    Zip Perm numbers
    A while back, I spent quite some time trying to find that information. However, once you have the right search criteria, it's pretty easy to get Google to cough up the specific docs on Huber's site:

    Page 23 of The Zip System Architect Booklet:

    And slide 10 of the Zip-R Sheathing Overview:

    In both cases, they're referring to the 7/16" version though. I would assume the 5/8" would be a hair tighter.

  8. user-1041981 | | #8

    Response to Christopher Welles
    Thanks, Chris. Page 24 of the Zip System Architect Booklet shows it as 2-3 perms in the picture. Wonder why they don't describe it anywhere in the text or in the table on page 31.

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