Rigid Boardstock Insulation Moisture Management Issues

Rigid Boardstock Insulation: Friend or Foe?

“When the message is absolutely critical, and not heeding the message increases the likelihood that a disastrous outcome will occur, then repeating the message is (or should be) a professional imperative! This has never been more true than with the issue of specifying and installing rigid boardstock insulation exterior of WRB’s and exterior sheathing on the exterior building envelope.”

The preceding paragraph is from the introduction to John Koester’s new white paper on potential moisture management issues architects, contractors and building owners face when they choose to use rigid boardstock insulation directly behind the exterior veneer of the building envelope (see image below). Normally, we release these articles after they have been published in industry-related magazines; however, this one addresses a topic that is so timely, we are going to release it immediately via our electronic newsletter, our website www.MTIdry.com and our social media sites. There is absolutely no charge nor are there any other conditions to access this article. It is immediately available as a PDF document via the link at the end of this article.

The following are some highlights from the “Exterior Rigid Boardstock Insulation Moisture Management Issues” article.

  • Most boardstock rigid insulation has some moisture-resistant characteristics.
  • When layered against a weather-resistant barrier (WRB) on exterior sheathing, an undrained cavity/void will be created that may entrap moisture.
  • Installing a thickness of rigid boardstock insulation over WRBs and exterior sheathing may have an impact on the fastening patterns and/or structural requirements to secure thin veneers (stucco, adhered thin stone and thin brick and various other siding systems).
  • Rigid boardstock insulation may have dynamics of its own.
  • Installing a thickness of rigid boardstock insulation over WRBs and exterior sheathing will impact exterior building envelope rough openings…

The article goes far beyond simply pointing out problems. Through the use of text and numerous detailed drawings (17) it shows how to solve or avoid the problems. We hope you find this information helpful, as well as timely. MTI believes that too much time is spent on the energy-saving side of the building envelope detail while often ignoring the moisture management side of the equation.

Building envelope moisture management must be equally involved in the building envelope detail if sustainability and energy efficiency are the goal!

Download the Rigid Boardstock White Paper

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Creating Sustainable Rainscreen Building Envelopes: It’s Like Motorcycles and Rain Suits!

Sustainable building isn’t possible without moisture management.  And for those forced to live or work in a building without moisture management, life becomes a health and safety nightmare.  Bold statements, but totally supportable.

According to the HUD’s Path Project, “Moisture, in all of its physical forms, is commonly regarded as the single greatest threat to durability and the long-term performance of the housing stock.  Excessive exposure to moisture is not only a common cause of significant damage to many types of building components and materials, it also can lead to unhealthy indoor living environments.  A long list of serious adverse effects can result from moisture problems in houses.  There is wide agreement that successful management of moisture in its various forms is essential for houses (buildings) to be durable, safe and energy efficient.”  In its 2004 report, the Path Projected listed the following outcomes of uncontrolled moisture in the building envelope:

  • Decay of wood and corrosion of metals
  • Infestation by termites and other destructive insects
  • Negative impacts on indoor air quality
  • Growth of mold, mildew and other biological contaminants
  • Reduced building material strength
  • Expansion/contraction damage to materials
  • Reduced thermal resistance of wet insulation
  • Premature failures of paints and coatings
  • Damage to building contents
  • Negative effects on building aesthetics

Enter the key phrase sustainable rainscreen building envelope into Google and you will get more than 18,000 results, including MTI’s “Drainable is Sustainable” presentation delivered at last fall’s technical meeting of the Sealant Waterproofing and Restoration Institute.  A key point of the presentation is that a moisture management solution for the rainscreen building envelope requires a systemic/holistic approach.  There is no single magic bullet; it takes a well-thought-out, coordinated system of products and processes designed and implemented by a team of professionals working collaboratively at every stage of the project to reach a successful outcome.

To illustrate the importance of a coordinated system in moisture management, I used the analogy of a motorcyclist riding towards an approaching storm in that presentation.

“It’s a nice sunny day, so I decide to go for a motorcycle ride.  Being an experienced motorcyclist, I always have raingear in my saddlebags because it’s summer and anything is possible!  As I move through the countryside, I notice that the sky is darkening and a storm is imminent so I pull over and put on my rain suit.

In a matter of minutes, the rain starts.  It’s light at first but soon becomes heavy, and it’s coupled with a driving wind.  Rain is forced around my windshield and into my eyes greatly limiting my ability to see the road.  Water cascades off my helmet and runs down the back of my neck soaking my shirt.  The water on the highway flies upward leaking into my boots through the seams and around the tongue.  To make matters even worse, it’s a hot, humid day so beads of condensation start to form on the inside of my rain suit making for an increasingly miserable ride!  Obviously, even though I thought I was prepared for rain, I hadn’t looked at all possibilities.”

Even though I had a collection of items designed to keep me dry, I hadn’t thought out the outcome fully, and I hadn’t properly combined the items into a functioning system.  If I had used goggles or a helmet with a visor, I could have seen the road better.  If I had used the hood on my jacket and worn it under the helmet, I wouldn’t have gotten rain down my back.  If I had used a rain jacket with vents, air could have moved around inside the system and reduced the condensation. Finally, had I worn rain boots with my rain pants lapped over the top of the boots and fastened snugly, I wouldn’t have got wet from the water spraying up from the road.

So what can be learned from this analogy about the importance of a system in solving the building envelope moisture management problem?  It takes many products, put on in the right order and at the right time, to create a positive result. We need to look at how many factors are in play and then employ several moisture management solutions as part of a system to solve the problem.

This same idea of a coordinated, multi-component solution can be applied to the people designing, specifying and constructing a building.  Gone are the days when designers, specifiers and contractors could successfully do their jobs in a vacuum.  There are just too many new products, processes and complex codes for the “Lone Ranger” approach to work.  Everyone must collaborate and communicate if a sustainable, healthy building is the goal.

Those are my thoughts; I welcome yours!

HD Big Twin