Moulded, Preformed Flashing Systems

20 – July 1975

These systems consist of various assemblies of metal sections with and without flexible plastic sheet components.  they are manufactured for use as roof edge, wall or curb flashing and expansion joint systems. CRCA has been asked to approve several of them.

It is not CRCA policy to approve products by trade name.  Conversely generic approval in this case in considered too all-embracing due to the existing and distinctly possible future variations between the different systems.

The roofing industry faces the dilemma of how to predict the long term effect of the introduction of newly developed component products into established roofing systems.  Any apparent conservatism of roofing contractors towards new products is not based on prejudice but on the vital need to avoid unreasonable risks.  That there have been some expensive failures is well known.

To help avoid such unreasonable risks, CRCA has established a procedure to be followed before acceptance of any new product.  Probably the principal element of this procedure is time – time for the new product to be installed under varying Canadian climatic conditions and time for a reasonable assessment of the durability of the product under the same varying climatic conditions.

The CRCA Technical Committee has studies the literature on the subject systems and has received some field reports.  At this time the committee feels it cannot go farther than to suggest some general guidelines for the use of these systems.  The guidelines are based upon practical experience of what happens on a roof during application and subsequent weathering.  It is hoped that these guidelines will help to avoid some possible problems.  At the same time, it is recognized that some of the products have been on the market for years but do not seem to have received national exposure.

The suggested general guidelines are:

  • A metal cant strip at wall or roof edge should have the triangular space beneath filled with insulation to minimize the danger of condensation if warm humid air should be able to leak from inside the building and come into contact with the cold metal.
  • Any in-wall reglet in a poured-in-place concrete wall is prone to have concrete break off in places along the top edge – particularly when concrete forms are removed. These placed must be carefully prepared to prevent water getting behind the flashing.
  • Installation of any reglet on top of a parapet wall cannot be considered good roofing practice (see CRCA Specification Manual page 12.6 Spec FL 111A).
  • Any system requiring nails or screws through the waterproofing element at or near the top of the cant should have the specified cant height closer to 8 inches (the minimum recommended height for nailing of flashings of any kind) rather than the normal cant height of 4 inches. Furthermore, it has been found that these nail or screw fastenings tend to get loose, requiring almost annual tightening.
  • Bellows type low profile expansion and control joints are not approved by CRCA for installation at roof level. They should be elevated on cant strips or curbs and, where water might be expected to lie, they should be well above roof level.  Further, as with any fire wall coping or fabricated metal expansion joint, they should be protected where even normal-in-service roof traffic passes over them.
  • Suppliers and specifiers of any system or detail using a flexible plastic sheet should ensure that the material will withstand the climate in which it will be used and that the joint installation is practical under normal adverse outdoor conditions at the time of year it will be required. It must be recognized that roofing application is, of necessity, a rough filed application and not a shop job.  Finally, these plastic sheets must have cold weather flexibility, resistance to fatigue to give a respectable service life and excellent bonding not only at the sheet joints but also at those joints where the sheet has to be bonded to the roof membrane.