Roof Gutters, Supports, and Seams – Part II

In a recent article, we discussed building damage from rains that overflow where rear gutters are installed at a insufficient capacity or are not properly maintained to verify and maintain free flow of draining water from the rooftop.   We are going to continue looking at that topic today, but we are also going to examine some of the relationship between systems deterioration and expanding and increasing damage to building systems.

When we talk about upkeep and preservation and maintenance of roof systems, the topic of accelerated deterioration will often be mentioned.  Infinity Design Services, a local DC company, specializing in historic masonry restoration, in their website:, explains the non-linearity as follows:

The non-linearity of the deterioration curve is a crucial aspect to comprehend when analyzing and understanding the aging and degradation of historic masonry and associated lime mortar. As these materials deteriorate, their decay occurs at an accelerating rate, through a series of compounding effects.  These compounding effects of deterioration can be described in terms of intensifying, exponential, and increasing at an accelerating rate.

The context of accelerated deterioration applies to roofing systems as well. In the first part of this topic, we discussed the gutter supports which had resulted as a shearing resistance failure as the fascia board under the modified bitumen membrane rotted away, due to improper coverage from a spanning metal flashing.

Some of the most important characteristics or details of gutter systems follow:

  1. Grading for Slope: Gutters are installed with a slight slope or pitch to facilitate water flow. This slope ensures that the rainwater naturally moves towards the downspouts or drain outlets. Typically, a slope of ¼ inch per 10 feet is recommended, although the exact slope may vary depending on the gutter system design and local building codes. The slope allows water to flow downhill, preventing any water accumulation or stagnant areas in the gutters.  

The next picture below shows the full length of the gutter with water accumulated and stagnant in a belly type area at the middle.  The gutter has sagged and no longer is properly graded.   As areas of the fascia board have rotted, fasteners which connected and supported the gutter in a linear but slightly sloped installation have now failed.  As a result as a result the gutter sags in the middle and stays nearly full of water.

full length of roof gutter

2. Drain Outlets: Drain outlets, also known as downspouts or leaders, are vertical pipes attached to the gutters at regular intervals. They serve as the exit points for the collected rainwater. The gutters are designed to direct the water towards these drain outlets, which are positioned to ensure efficient water flow.   In historic neighborhood such as Capitol Hill downspouts or rainleaders are often coincident with underground drain pipe hubs. Downspouts often extend down the side of the building and can be connected to these underground drainage systems or directed away from the foundation to avoid water pooling near the building and foundation. 

In the picture below you can see the west edge of the gutter at the property where we are working, the neighboring gutter, yet further to the west has a clear outlet which let’s water flow, even in rainstorms.

west edge of roof gutter

3. Seams in the Gutter System: Gutters are typically manufactured in sections that are joined together to cover the entire length of the roof’s edge. Seams are the points where these gutter sections are connected. The most common type of gutter seam is a slip-joint connection, where one section of the gutter is seated into another and is secured with screws or rivets.  Seams play a critical role in the functionality and durability of the gutter system. They need to be properly sealed to prevent leaks. Improperly sealed or damaged seams can lead to water leakage, which may cause damage to the building’s structure or surrounding areas.  To maintain the integrity of the gutter system, it is essential to inspect the seams regularly for any signs of damage, such as gaps, cracks, or separation. If any issues are detected, they must be repaired by resealing the seams or replacing the damaged sections of the gutter.  In some cases, seamless gutters are used to eliminate the need for seams. Seamless gutters are custom-made on-site using a die machine, similiar to an extrusion, but actually just bending the coiled metal, resulting in a continuous length of gutter that fits the custom dimensions of the roof’s edge. This minimizes the number of seams and potential points of failure, improving the overall performance and aesthetics of the gutter system.  In summary, gutters collect rainwater by being positioned along the roof’s edge, are graded with a slight slope to facilitate water flow, and use seams to connect the gutter sections. The seams must be properly sealed to prevent leaks and ensure the efficient conveyance of rainwater away from the building. 

In the next picture below, you can see that water is spouting out of an area of a seam.   Unlike a seamless gutter, gutter sections like this half round historic style gutter have seams at joints within areas less than about 16 foot.  This particular seam though was really unnecessary and only added or built in this configuration as the original builder took a shortcut to save money and use two partial sections of scrap or excess material instead of using a new full length piece of gutter material. 

seam of the roof gutter

In the next even closer view of the same area, you can clearly see that the leak is spouting out of an area below the gutter and not a result of water running over the edge or lip of the metal gutter.

seam of gutter closup

In an upcoming future article, we’ll talk about the benefits and potential shortcomings inherent in the use of gutter leaf guards.  While gutter leaf guards can be helpful in some ways, they’re not a perfect solution and still generally require maintenance.

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 complete the webform below and drop us a line and we’ll respond if we can help.

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