Ponding Water On Low-Slope Roofs – Part II

Everything you need to know about ponding water on low-slope roofs

In a recent article, we talked about the problems associated with ponding water on low slope roof surfaces.   It continued that discussion today and we look at the areas of rooftop curbs without crickets or provisions to shed rooftop water and flat seams that are in areas that become submerged in ponding areas.

Ponding Water Example – Skylight

The picture below shows an example of a skylight, in the middle of the field of a roof layout. This skylight is relatively small, but there’s also a ponding area just on the upper side of the curb. One way to fix an issue like this, at the time of original construction is to frame a small cricket. A cricket is a small angled buildup com up like a triangular type shape that will shed water away from a ponding area.

ponding water skylight roof

The location shown in the photo above, the incident of ponding water has deteriorated the roof coating, overtime. That roof coating, after being submerged after each incident of precipitation and then stang submerged for a significant amount of time because of the roofs inability to shed water properly has allowed the roof coating area to stay submerged and therein calls the situation where the roof coating has deteriorated and were eliminated from the roof substrate surface because of its exposure to constant residual water.

Eventually, over time areas like this can cause leakage. Particularly, where ponding water is condensed it with roof seams come of what I will find this way through in time, generally this type of deterioration happens in a time span shorter than the intended lifespan.

Ponding Water – Rooftop With a Parapet

The picture below shows another area of ponding, at a different roof. This area of ponding happens to be near the front termination of the roof where the rooftop is built with a parapet at the front of the building.

ponding water parapet roof

At this particular location, there is a scene in the flat laid single-ply modified bitumen roof membrane materials.   The area of pond income as highlighted in the picture below, is within some of the adjacent seams come up but this picture happens to have been taken a few days after the most recent rainfall and during rainfall and the time that follows rainfall coma the area of pawning will actually be greater and cover some of the same areas which is problematic.

ponding water on low-slope roofs

In the picture below, you can see the area of membrane seams more closely.   Modified bitumen roof membrane is applied in thin layer which overlap.  It’s best practice to avoid seams that run in the direction of the flow of water,  Seems of this type that we’re technically allowed in conditions where there is an overlap of at least 3″. Also, at the overlaid material, it’s best practice to trim the bottom corner so that the corner has a slight radius.   The radius cut at the edge avoids a thin corner which is exposed on 2 sides.

The same in the picture below though terminates with a sharp 90゚ corner which is not best practice and may be out of tolerance for the manufacturer’s installation requirements..

membrane seams

How Important Is Waterproofing

Smart proactive replacement, construction, upkeep and maintenance of low slope roof systems requires an enthusiastic interest and understanding of waterproofing principles and building science.   Here in Washington DC, historic and modern residential and commercial buildings are extremely expensive and the roof and related systems provide the shield that preserves the building. 

We encourage all of our clients, and all readers of this article and to our blog in general, to prioritize the value of quality construction and building maintenance, and develop a relationship with our company.  You can learn a lot more on our blog.  Feel free to check it out.  If you have questions about the roof and related systems of your building in Washington DC, fill out the webform below and drop us a line.  We will be in touch if we can help.

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