Weep Screeds and Halloween

There actually is a connection between the most commonly used weep screeds and Halloween — they both can involve some scary outcomes!  The purpose of a weep screed in thin veneer wall is to provide drainage at the bottom of the thin veneer wall. Unfortunately, the manufacturer’s literature often states that this drainage space will come from the formation of a shrinkage crack. This is neither a predictable nor adequate solution for providing the necessary drainage of moisture at the bottom of a thin veneer wall.

A paradigm shift is needed when it comes to draining thin veneer walls. Most architects and builders now recognize the need for a drainage plane (commonly referred to in the industry as a drainage mat) behind thin veneers. These products create a space behind the veneer that acts as a capillary break and a transport mechanism to move water that gets into the building envelope down to the bottom of the wall. The problem arises when that moisture reaches the base of the wall; the most commonly employed weep screeds restrict the flow out of the wall because of that pesky shrinkage crack! And no, those tiny little holes are not for drainage. Again citing the manufacturer’s literature, they are for “attachment purposes (not weeping).

Moisture-related failure of walls is not as much about volume of water in walls as it is about the time that some moisture is allowed to remain in that wall. If an adequate opening isn’t available at the bottom of the wall for moisture to exit and adequate airflow to occur, the wall is ripe for failure.

I prefer to remain optimistic about the building industry, but I recently read an article in a national building trades publication on the correct installation of adhered masonry veneers that set my optimism back a bit. As many of you know, adhered concrete masonry veneers have experienced a large number of moisture-related issues when not installed properly. Many articles have been written about this issue including “Best Practices: Adhered Concrete Masonry Veneer” by Mark Parlee that appeared in the Journal of Light Construction. Parlee, who is a builder as well as a forensics expert, notes in his article that ACMV walls have now become a trigger for inspections because of the large number of moisture-related failures they have experienced. He goes on to state that the solution is “drainage.”

Back to the article I read. It implied that drainage was necessary, but it referenced the use of two layers of WRB to create that drainage. That is a very old technique, proven by testing to retard the rapid transport of moisture out of walls. It does not provide the minimum drainage space specified by respected scientists like Dr. Joseph Lstiburek. In his article Mind the Gap, Eh! a minimum 1/8” gap or void needs to be present to create a capillary break and an effective drainage mechanism.

The building trades magazine article also mentioned the use of a weep screed, but it did not indicate what to look for in an effective product. Remember, the holes are for attachment, and a shrinkage crack isn’t predictable. I am disappointed that while we seem to embrace the goal of better buildings, we still employ old, outdated techniques even though many of the new materials we build with don’t work with the old way of doing things.  We need that paradigm shift!

You need to look for a weep screed that provides frequent, large openings for drainage. They do exist. Without “real” drainage space behind the veneer and “real” openings at the bottom of walls, you will wind up with a moisture “trick” rather than the “treat” of a beautiful, long-lasting building. Happy Halloween, hope you get a treat!

*For more information about weep screeds and weeps at the bottom of walls, download the MTI article “MTI-014: Getting to the Bottom of Moisture Management” in the MTI Library at http://www.MTIdry.com.

ACMV wall failure in a Midwest hotel.

This photo shows a moisture-related ACMV wall failure in a Midwest hotel.

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

insulation_moisture

Holes Keep Walls Dry – Fact or Fiction?

It seems counter-intuitive to add holes to a wall to keep the building envelope dry, but it is a necessity in rainscreen building envelopes. In preparing for a presentation we will be doing at the Sealant, Waterproofing & Restoration Institute 2010 Fall Technical Meeting this October, I came across an excellent article by Brett Newkirk entitled, “Creating Holes to Stop Leaks” in the August issue of The Construction Specifier. If you have any reservations about the necessity of drainage in rainscreen walls, I encourage you to read this article.

In summary, Newkirk posits, “Holes or weeps are needed in buildings constructed using water-managed cladding systems…because it is anticipated that water will penetrate the veneer and drain down the underlayment and exit to the exterior.” We need to provide a drainage plane and weeps (holes) at the lowest point in the wall to make this possible! According to Newkirk, “The only type of wall not requiring holes is a ‘barrier’ system…and that is an extremely difficult system to successfully achieve 100% of the time.”

So what’s the quick take? In MTI’s opinion, and it is an opinion based on testing and research, if you are building with a rainscreen building envelope, you need to provide a drainage plane and weeps (holes). The drainage plane needs to be a predictable void behind the veneer; it also needs to be a predictable pressure equalization plane. The weeps are an integral part of this drainage plane system, and they need to be placed frequently and at the lowest point of the wall.

Newkirk goes into great detail about the why and where of “holes”. The article is available online, and I encourage you to read it. Those are my thoughts, as always, I welcome yours!