Of Parapets and Peril

MTI has put together a series of articles on “special moisture management problem areas.”  The first of these articles was the Window Rough Opening piece we blogged about last time.  This month we are making available “Moisture Management of Parapet Walls.”  The following text is an excerpt from that article.  The entire piece can be downloaded at http://www.mtidry.com/news/ParapetWallArticle.pdf.  You can also find links to this article and the previous “Moisture Management in Window Rough Openings” on our News an Views page at http://www.mtidry.com/news/index.php.

Parapet walls – what are they good for?  Parapet walls perform a number of important functions:

  • They can be designed in various shapes to create a desired façade
  • They can be designed to hide roof top equipment (AC units, etc.)
  • They help prevent roof edge blow off by diverting air flow up, over and away from the roof edge.
  • They can be a stable termination point, for roof edges and flashings.

However, even though parapet walls perform a number of important functions, they are moisture management headaches!

The phrase ‘Out of sight out of mind” is, unfortunately, the rule of the day with construction details that are not easily accessible.  Parapet walls fall into this category.   The required timely maintenance is neglected because of this and regrettably, the need for maintenance becomes apparent only as a result of a failure such as a leak.  On top of this, parapet walls have a rather rough life since they are subjected to wind, dramatic temperature changes, moisture from three sides and roof system stresses.  The result is a construction detail that is both neglected and abused.

The answer to the question “Why do parapet walls fail?” seems obvious.  The solution is just as obvious – design them to be better and maintain them properly.

The most fundamental rules of moisture management “Keep moisture away from, off of and out of a construction detail” and “Move moisture away as quickly as possible” always apply.  However, two additional practices should be employed.  First, use good moisture management design and identify and isolate the moisture risk zones in such a way as to separate high risk from lesser risk.

Like all structures a parapet wall suffers the fate of its roof – the coping.  Failure of the coping is closely followed by wall and interior failure.  Use the link above to access the entire article with proposed solutions to the parapet moisture management dilemma.Adobe House with Parapet