Roof Problems Leading to Siding Rot Part I

In the last week’s blogs, we looked at the closing parts of a series related to common signs of low quality in installation of modified bitumen roofing, examining a variety of types of different problems and quality control issues with modifed bitumen roof installations. We also talked about the best practices that can be learned from examining and correcting the problems created by low quality roofers. Our company happens to specialize in that type of corrective work because the demand for it is so high and the supply is so low.   So, good quality roofers, like our company can continuously improve and do a better job by learning from the mistakes of others.

In the picture below you can see an example of a modified bitumen roof membrane on a flat roof.  This particular case a continuously joined aluminum coping has been installed on top of a parapet wall. 

modified bitumen roof membrane

The parapet wall as shown here; however, previous to this photo was covered with a different aluminum copining.  It was built from similar field bent metal but the roof membrane and the coping were installed before the siding.  

The next picture below shows the parapet and coping on top of the exterior wall of the building. We removed this original coping, install by others, because the original coping was too small to fully cover the top of the siding.   When the siding was installed, it was installed just outside of the edge of the coping covering.  This is incorrect, in the reverse order and allowed water to run right down behind the siding.

In the next picture below, you can see the edge of the trim board at the top of the wall protrudes beyond the edge of the metal coping.

trim board

In the case of cementitious siding, and really almost any type of siding, for that matter, when there’s a horizontal surface that protrudes beyond the cover above, it should be flashed with its own separate z-flashing.  There are all the types of flashings which are used to create a waterproof transition from one type of materials to a next. In this particular case, aluminum is one of the most common and preferred types of materials for roof flashing at transitions of a roof to cover the edge of the siding below. In most cases, the siding work or installation would be complete before the aluminum coping was installed at the roof parapet. This work’s particular sequence may have been reversed because of new construction elements being done out of order by the developer in using cheap contractors and not managing the work properly.

In the picture below, you can see two different images, the first image on the left side shows the full length of the parapet, and then an up close version of that same parapet marked with the labeled parts on the right.  You can see that although the trim board at the top of the vertical siding wall is a typical part of construction, it should not be exposed, as it is in this particular case. Normally the top of the takeboard trim is either covered by the coping or by an extended piece of partially overlapped flashing that goes from underneath of the coping and extends beyond to cover the top of the rake board.

rake board

The picture below shows the coping after completion of modifications and repairs.

coping after completion of repairs

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.

On Key

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