Modified Bitumen Roofing and Telltale Signs – Part VI

The outline for the entirety of this multi-part series on modified bitumen flat roofing follows.  In two different articles this week we will talk about telltale signs of experience and the items for today are highlighted in the outline below:

  1. What is Modified Bitumen Roofing?
  2. Hard Requirements 
  3. Best Practices
  4. Telltale Sign Of Experience
    1. Uniform substrate
    2. No 90-degree outside corner
    3. Double overlay at pipe penetrations
    4. Crickets at curbs and bounded areas
    5. Careful detailing of flashings
    6. Gravel stops instead of drip edges
  5. Core Sampling 
  6. Rounded Corners and Why They are Better
  7. Bleed-out as a Sign for Proper Application 

We pick up today’s article right where we left off earlier this week. We start by talking about crickets at curb and bounded areas.

Crickets at curbs and bounded areas

A typical low slope roof surface, in the simplest sense, runs straight from a high side down to a low side.  The rear termination, and the typical layout, and the upper termination, may be parallel to one another, but they are generally not in the same horizontal plane because the low end is significantly lower than the high end.   This simple layout works very well, but there are typically, especially in historic buildings, chimneys and other elements which can break up that otherwise simple flow of water created by the low but continuous slope.  Other than chimneys, some of the other most common elements which break up that simple continuous flow would be curbs at elements such as skylights and or HVAC equipment, and rear ells where there is a recess or area cut out of the typical rectangular shape of a roof or building footprint.

A buildup is needed in the inside corner at a rear ell, for example. Otherwise water can get stuck in that inside corner without sufficient slope for it to drain out of the nook. The same thing can happen around curbs and chimneys. Buildups which are set with a small ridge and flow around elements that are directly in the field of the roof are referred to as crickets.  Crickets are generally set where there would otherwise be a small ponding area.

The problem is that on historic building construction in Capitol Hill and Washington DC, crickets are often omitted. Even in the areas of rear ells, a buildup in the roof is also often emitted. We considered it a very positive sign when we see that a prior contractor has taken the time to install and build up properly to avoid ponding at these areas at curbs and chimneys and nooks above rear ells.

Careful detailing of flashings

Once a roofing contractor or inspector is familiar with installing roofing and best practices they will notice these differences almost immediately when looking at how flashings are detailed. This is one of the big differences between professionals and amateurs.  Counter flashing, for example, when set into or on a masonry wall should always be set into a reglet or ragle. Termination bars are acceptable alternatives to counter flashing in many cases, but amateurs don’t often use termination bars. In many cases low quality roofers come from the residential roofing industry and are used to installing shingles on pitch roofs in the county or the suburbs. Those roofers may think they can get away with installing flat roofs and often they do get away with it, but they also often leave behind many problems related to quality, particularly in the area of proper flashing detailing and installation.

detailings of flashings

Gravel stops instead of drip edges

Drip edges are commonly used at the sides of balcony roofs, for example, in certain configurations.  In most cases though drip edges are only really needed where water is intended to flow off a roof into a collection system such as a gutter.  At other areas where the roof ends in a flat position but does not have an intended flow of water off of that edge, a gravel stop is a better option. Professional roofers know this difference but often amateur or low quality roofers will grab whatever material is necessary and often drip edges are slightly cheaper than gravel stops. When clients pick a roofing contractor just based on cost they will normally get a roofing contractor who will skip this subtle but important difference in terms of quality.

Over long periods of time even with areas that do not have highly directed slope, when a drip edge is installed, but the water is not fed into a gutter system, that water will run down the face of the building closing slow but insidious damage to the facade. In time drip areas will result in staining and then slow insidious deterioration which can cause rot and or ruin of the facade materials.

The picture below shows an example of a roof edge, not where the gutter is installed, but adjacent to the gutter at a nearby front porch, a gravel stop should be installed there since there is no gutter at the edge of the roof.

gravel stops

Upkeep, Care and Maintenance of Washington DC Roofs

This case study is a perfect example of why a professional roofer should be used for all types of roof installation, even things that seem as simple as a balcony.  Consulting with a roofing professional, like Dupont Roofing, familiar with the specific climate conditions and the building science of roofing in Washington DC is advisable to ensure the roof assembly is appropriately designed and constructed to manage the flow of water, ice damming, capillary action and condensation effectively.

The upkeep, maintenance, and general care of flat and mansard roof systems should be driven by an understanding and passion for historical methodologies, waterproofing principles, engineering and building science. Washington DC, a city built with both vintage charm and contemporary modernities, residential and commercial buildings of substantial value. 

The roofs of these buildings are their defensive shield from the harsh elements of nature. To our clients, as well as all readers of this article and our blog, we emphasize the importance of quality construction and active building maintenance.  Our website includes informative resources you can use to understand and learn about best practices on preservation of your building.  If you are in need of further guidance on the roof and its associated systems for your Washington DC property, we are here to assist, where we can. Simply contact us or complete the webform below and drop us a line and we’ll respond if we can help.

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