Rounded corners in Flat Roofing – Part IX

Earlier in the series on techniques and best practices for installation of  modified bitumen roof membranes, we talked extensively about different types of common defects or shortcuts taken wich lead to diabilitation or damage to roof membranes.

Everything in our series has focused on modified bitumen membranes.   Here below you see an example of a granulated APP modified bitumen overlay at the base of a concentric flashing at a pipe penetration.   The outside corner of this membrane has not only been rounded, but it has also been cut at 45° angles.  This type of installation method avoids the need for a sharp ninety degree corner.

app modified bitumen membranes
In some cases, APP modified bitumen membranes can have significantly less bleed-out that SBS membranes.

One of the elements that we also talked about was the fact that exposed edges or corners of roof membranes should be cut on a radius or rounded corner so that there is not a 90° or sharper angle exposed.  In a recent previous blog, we looked at several photographs of the outside corners of membrane terminations where the membrane corners are cut at 90° and not properly rounded. Rounding has to be done manually, with a knife. Stock materials essentially come on rolls, in a rectilinear type shape. The custom rounding has to be done where the at the end of a roll or at an overlaid cut.  Often this is required where he membrane terminates in the middle of the field or in the middle of an installation area without reaching the intended other side.

The picture below shows an inside corner in a TPO roof with an overlaid reinforcement.

overlaid reinforcement
The overlaid reinforcement is properly cut with rounded corners to avoid sharp outside corners.

Although TPO amd modified bitumen membranes are very different types of materials, some of the principles of installation of roofing work, not just in one material type, apply across several different types of flat roofing systems.

substrate base flashing
In the picture above, the substrate base flashing at a vent termination is rounded at the underlying layer and even at the upper overlay.
target patches
Pre-manufactured target patches at pipe penetrations are specifically manufactured rounded to avoid sharp outside corners.

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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