February 2, 2016

GreenBuildingAdvisor, Smart Membranes & 475

GBA has been a place to engage in debate with a seriousness of purpose. But the article Smart Vapor Retarders for Walls and Roofs on GBA is not serious. The article is full of strawman arguments, unsubstantiated claims, gratuitous personalization and bait & switch tactics. GBA failed to ask any questions of 475 while reporting the article.


Whitchurch RoofWe have real-world experience and we have data. The Whitchurch Passive House Cottage, in Middlesex Vermont, built by Chris Miksic of Montpelier Construction with Passive House consulting by Indigo Ruth Davis and consulting by Bill Hulstrunk from National Fiber, for owners Barbara and Greg Whitchurch, is one example of an unvented roof with INTELLO Plus inboard. The project was well suited up with data monitors during construction in 2014 – blogged by 475 here – and we’ve been getting updates. Greg’s readings from Feb 1st 2016, show moisture content at the outer roof sheathing of 8.1%. 

Corson-Ueno Presentation

Corson-Ueno Presentation

Kohta Ueno, a Senior Associate at Building Science Corporation, did a presentation with Chris Corson of Ecocor, at NESEA BE15 – on exactly the assembly the GBA article is focused on – with real world data: see slides 31-39 of the presentation here (pdf).

The renowned Federal German Institute for Civil Engineering or Deutsches Institut für Bautechnik (DIBt) has recently completed extensive third party verification of unvented vapor closed wood assemblies with Pro Clima DB+ and INTELLO smart membranes and has approved their use as code compliant in Germany. Read about it here.

The 475 worldview is not divided between computer simulation and actual experience. 475 is committed to using all the tools at our disposal to lift the quality of building, through: writing and trainings, drawings, computer modeling, real-world experience and data collection.

The Vapor Curve

The vapor curve matters. Contrary to what the article would have readers believe, while many materials have variable vapor permeability, the quality of the permeability curve is quite different from material to material. This difference matters. Vapor retarder paint is not close in performance to a smart vapor retarder. MemBrain has a less robust vapor curve than DB+, and a much less robust curve compared to  INTELLO Plus.  

We’ve carefully laid out some of these differences in our blog post Why The Vapor Curve Matters. INTELLO_membrain_MajpellWhen Joe Lstiburek is quoted in the GBA article, that smart membrane effectiveness is limited by maximum interior RH of 25% to 35%, he is mistaken. INTELLO Plus works effectively at interior RH levels of 50%. Read the INTELLO Primer. GBA should acknowledge that our smart membrane works at a much wider range of interior humidity.


GBA never asked to see the 475 WUFI Pro models. GBA doesn’t know what’s in the WUFI models. Yet the article has further expert opinion telling us what’s in and not in our WUFI models. Strange.

“The 475 Approach”

475 always takes a whole systems approach to making high performance assemblies. While every component is important, how they work together is even more important. As insulation levels grow and expectations of comfort and efficiency rise, assembly drying capacity and reserves are increasingly critical. Experience is a tool. WUFI is a tool. Detailing continuity and training are tools. Blower doors are tools. We use all the tools at our disposal.  

475 recommends vented assemblies – they are the most robust and lowest risk assemblies possible. See our blog post A high performance roof should be vented – how to do this properly.  

Smart vapor retarders, especially INTELLO Plus, can significantly increase drying reserves of assemblies. But contrary to what the GBA article would have readers believe, the addition of INTELLO Plus is not the end of the answer, rather, it is the start. The details must be worked through and the job site execution done properly. Consequently a pencil hole will not endanger the system.

We’ve gained our customer’s trust because we are focused on their specific requirements and solutions. 475 is committed to helping build the highest quality, highest performance, most robust and environmentally sustainable buildings. We’re proud to be part of teams executing some of the most exciting and ground-breaking work across the US and Canada.

Pushing and Push Back

The genesis for developing a safe (foam free) unvented roof came not from marketing research but in working with professionals on flat roof Passive House projects of high insulation levels, where vented roofs would not be effective.  (See two in-depth 475 blog posts on this subject here, and here.) This is the case of the Whitchurch project in Vermont.   

The other impetus for thinking about making a safe (foam free) unvented roof, was in hearing of home retrofits dominated by the application of toxic spray foam, where installers were looking for a safer viable alternative – like this leading insulation contractor in Massachusetts.

We don’t push products. We do push for more predictably energy efficient buildings, and a less toxic environment. Our North Stars are Passive House and Greenpeace. Both are where some of the the most interesting and meaningful work is getting done on the planet.

Is It About Foam?

It is an odd thing that GBA has written this article which on its face works to unfairly discredit an assembly where there is no evidence of damages. While on the other hand GBA spends disproportionate ink in support of spray foam insulation as apparently a low risk approach – a method of insulation that has a history of inflicting both health damages to workers and occupants as well as providing failing performance. What’s going on?

We think the spray foam industry’s dominance in construction is a clear victory of chemical giant marketing over good science. We understand foam isn’t going away, consequently our motto is Less is Best.


475 has big ambitions to help move the enormous US construction industry toward truly sustainable high performance. 475 is happy to challenge convention where we think it falls short, and engage in informed debate. Let’s make better buildings.


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2 Responses to GreenBuildingAdvisor, Smart Membranes & 475

  1. Jeremy Avellino February 11, 2016 at 11:54 am #

    Well said! I saw more holes in that GBA article than in a typical Tyvek WRB installation. My first thought when reading it was why they clearly hadn’t brought 475 into the discussion. Good followup. Pushing a holistic airsealing + insulation approach based in proven science and real world case studies seems to challenge too much of the multi-billion dollar US construction industry right now. I’m glad you keep doing it. Its so necessary to move our industry into a more logical, transparent, regenerative approach.

  2. Martin Holladay August 10, 2016 at 3:35 pm #

    A recent GBA article summarized Kohta Ueno’s conclusions about the unvented roof details promoted by 475:

    ““It works,” Ueno reports, “because the assembly includes an interior variable-permeance membrane, because the builders tested for airtightness, and because the roof has no permanent shading. I trust the Passivhaus builders to put this together. But on a normal job site? I don’t know.”

    In comments posted on GBA, Ueno noted that inward solar vapor drive helps keep this type of assembly safe. “Any stored moisture is blown out of the outer sheathing and pushed inward,” Ueno wrote.

    This approach requires perfect detailing and attention to airtightness. Moreover, the roofing must get enough sunlight for the inward solar vapor drive phenomenon to work; that means that north-facing roofs or roofs shaded by trees are much riskier than south-facing roofs that are unshaded. Ueno concluded, “I’d definitely be concerned releasing this assembly on the general construction market.”

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