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GreenBuildingAdvisor, Smart Membranes & 475

February 3, 2016

A regular platform of building science debate is the GreenBuildingAdvisor (GBA) website. We’ve been contributors to GBA and engaged in debate there – always with a seriousness of purpose. So it was with great surprise and frustration that we read Smart Vapor Retarders for Walls and Roofs on GBA. No questions were asked of 475 in preparing the article. The article is full of strawman arguments, unsubstantiated claims, gratuitous personalization and bait & switch tactics. Whitchurch Roof



We 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 owner 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 the exactly the assembly the GBA article is focused on – with real world data:  see slides 31-39 of the presentation here (pdf).

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 are vapor permeable 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 careful 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 the limits of 25% to 35% interior RH in relation to smart membrane effectiveness, he is mistaken. INTELLO Plus works effectively at interior RH levels of 50%. Read the INTELLO Primer.


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.  

Smart vapor retarder, 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

475 recommends vented assemblies. See our blog post A high performance roof should be vented – how to do this properly.  

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?

We think the spray foam industry’s dominance in construction is a clear victory of chemical giant marketing over good science. (See our blog series Foam Fails.) And we understand foam isn’t going away – some of our products are foam. 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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