Exterior Wall Trim Joining Roof Terminations

Exterior wall trim joining roof terminations – a detailed guide

Wall trims, at the exterior of buildings, seal though the space between the top of the exterior walls of the building and the roof system. 

There are three main types of wood wall trims:

  1. Fascia boards
  2. Rake boards
  3. Soffit boards

Functions of a Trim Detail

At flat roof buildings, these trim details work very similar to the way they work and are configured with pitch roof buildings, but particularly in the case of flat or low-slope roof buildings, there is generally an area to be spanned or covered between the start of the framing and the top  of the brick exterior wall of the building. 

Many rowhomes, in historic cities such as Washington DC were built from brick structural walls. Brick creates a durability and fire resistance that wood alone cannot provide.   The vast majority of historic buildings in the center of Washington, DC, for example are build with structural brick.  The only problem though is that, at the roof  brick and wood must be joined in a way that is somewhat seamless and not opened to the exterior elements and rodents.  

The picture below shows an example of a rowhome built slightly higher than the adjoining brick building.   Like an end unit in a row, the top of the exterior side of this building is exposed to the elements.  You can see the exposed area of rake board at the top of the exterior wall at the side of the building.  These exterior wall trims, such as fascia, rakes, soffit, and cornice make those connection points join between the roof and the exterior facades.

In this particular case, the rake board is actually missing, it has deteriorated and fallen from the building and blown away over time in high winds. The board that’s exposed is actually a rafter at the rim of the roof framing. There is intended to be a rake board, at this location, a type of trim board installed over top of the wood framing to join to the brick side wall below.

rowhome built higher

At the exposed side of this building, you can see that the historic brick wall is in need of upkeep, repair, and restoration. Much of this brick should be repointed or tuckpointed.  Most roof companies cannot restore or repair brickwork, but our company is different. Dupont Roofing specializes in and is focused on the flat roofs of the historic buildings of Washington DC and brick repair is a near constant need at or adjacent to the majority of flat roofs replaced or repaired by our company. 

You can see that without that rake board in place, there are exposed and open gaps between the relatively inconsistent brick wall top and the underside of the rafterboard.  The bare, exposed rafter is recessed where instead a rake board should be set proud of the remainder of the wall facade.

rowhome built slightly higher

Why Rake Board Is Important

The next picture shows an adjacent area from a different angle. Without the rake board in place, the next roofing contractor went and installed a modified bitumen membrane without properly terminating the end of the membrane.  Someone, in the past, even painted the exposed rafter as a cheap and dirty shortcut, to save a buck, instead of installing an overlaying, gap spanning rake board. If a rake board is in place, a drip edge is intended to be installed over thelatbrake board. That drip edge can be in the form of a gravel stop at a edge of the roof which is not intended to drain. The gravel stop is similar to a typical drip edge and includes a drip edge projection at the bottom of the bend In the constituting material, but particularly in the case of a gravel stop, the metal of the termination rises to an angle above the roof membrane before returning downwards to the drip edge at the bottom of the termination.

rake board missing

The next picture below shows an angle of the rear termination, this particular picture is looking upwards under the gutter. You can see the brick rear wall of the building at the right of a picture and then a 2x dimensional lumber board installed across above the top of the rear wall of the building. Normally, a 1x trim would be installed here instead of a 2x framing Lumber.  

Synthetic Materials Vs. Natural Lumber

Today, synthetic materials are often used at these locations, instead of the natural lumber which was used historically.   A few things have changed in the building supply industry, over the years. In the past several generations, lumber has become softer pertoday, delethe lumber that is harvested for tremble words is generally from fast growth lumber, harvested at the earlier years of the tree’s lifespan. This lumber is more susceptible to rot and deterioration. Particularly, As modern manufacturing techniques now harvest more of the wood material, the smaller pieces which would otherwise Go to waste or other uses are now incorporated back into wood boards in the form of a composition of smaller materials through glue and joinery such as a common finger joint type of board. These boards are comparatively cheaper but also have a decreased longevity.

As wood has become less durable, synthetic materials have also come onto the market to provide a longer duration material, but synthetic materials also have inherent shortcomings. For example, synthetic trim boards cannot be painted as well as traditional lumber materials with the same type of paints. Alkyd paints are significantly durable but do not all bond well to synthetic materials such as polyvinyl chloride otherwise known as PVC.   Latex paints have similar issues with bonding, and also are generally less durable than alkyd paints, yet many alkyd paints have been removed from the market because of concerns with environmental impacts related to carcinogens and volatile organic compounds.

You can see gaps and inconsistencies in the installation. Those gaps are particularly problematic because even though they are under the flashing between the rear roof termination and the gutter, essentially underneath of waterproof materials or a waterproof assembly, they are open from below which can allow rodents to enter the thin attic space of the building.

rear termination above gutter

The next picture shows the side, the horizontal angle of the side of the gutter and the edge of the fascia board, at the location where the low slope or flat roof meets the top of the rear facade. This picture is similar to a cross-section though and is a good place to view the elements, between the roof and the exterior rear facade, as they all come together. In this case, the particular pieces of the materials are somewhat disarranged and disjointed, but they still show each element in its intended area of installation which illustrates the concentric or overlapped nature of the waterproof membrane of the rooftop and flashing and gutter system.

edge of the fascia board

In this particular case, since the fascia board is warped and twisted out of shape and improperly installed, there is a large space under the fascia board, as shown in the picture above from the angle below the gutter. In this case that gap is so large that one can literally stick their hand up into the open area which then goes into the roof at a space. This is more than sufficiently large for any or almost all rodents to enter the building. Squirrels, birds, and many other types of rodents (even rats here in urban areas) are aggressive and tenacious, searching for areas of shelter and in the winter searching for areas of warmth.

gap in fuscia board

As a makeshift or halfway type of repair, over the years, probably years ago, somebody installed a metal trim or coil stock material over the area where the fascia board is supposed to be installed. It looks like they did this in the lieu of installing an actual fascia board probably to save a little bit of money, but an actual fascia board would fill this space better and extend to the proper location where the gravel stop or drip edge should be installed to terminate the modified bitumen flat roof membrane.

open gap in fuscia board

In the next picture below, you can see that there is a large open gap between the remaining drip edge at the roof termination and the wall below.   The roof projects out at least an inch or two beyond the face of the wall below.  This type of extending projection is not a problem and even sometimes functionally beneficial at the end of a pitched roof eave, but here at the rake (similar to a gable of a pitch roof) the extension is problematic.

gravel stop projects vertically  

The next picture shows the gravel stop at the neighboring roof. In this picture you can see that the gravel stop projects vertically above the horizontal plane of the roof. This vertical rise at the top of the gravel stop allows for a distinction in the direction of waterflow. Water that lands, through precipitation, on top of the roof will flow as directed by the grade of the roof system. With just a basic drip edge, water is intended to drain over the drip edge, a drip edge without a gravel stop will not separate the flow of water, instead it will allow water to flow, as guided by the grade of the roof, generally into a gutter for collection and continued diversion of the water.

The gravel stop, on the other hand, as opposed to a regular drip edge, will split precipitation or rainfall into two different directions. Water that lands just on the outer side of the ridge of the gravel stop will fall away from the facade of the building. The slight projection at the drip edge bottom, of the metal termination, will allow water to fall without running down the face of the facade.  This detail is subtle and works passively but extends and prolongs the life of a building facade.

gravel stop  

Gravel Stop And Leakage

Water that lands or falls on the inner side, the flat roof side, of the ridge will then be directed by the slope built into the configuration of the low slope roof and drain from the front towards the rear, in the case of this particular rowhome layout.

The next picture below shows a different angle of that same gravel stop. Here you can see that the edge of that gravel stop, where it terminates at the next neighboring roof, is not sealed or filled, the gap that’s open at that area should always be sealed up, at least with a gun applied asphaltic or elastomeric sealant. In this case, the space is open and creates a void which could also be a point of water or rodent entry.

edge of the gravel stop

Maintaining Flat Roof Systems In 2023

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. 

Unlike the majority of roofing contractors, as we can clearly see from the conditions abundant throughout the city, our company cares about quality and the longevity of your roof and building.    The biggest difference overall though, is knowledge and understanding. Often, we look at the near limitless amount of poor workmanship done by other roofers throughout the flat roofs of the city. It’s a complicated issue.   It’s easy to dismiss the issue and simply say they’re bad contractors, but that’s a lazy way of looking at the context. There’s more to it than that period often, the vast majority of work that we consider to be defective, short We’re lacking in longevity, wore poor quality or poor workmanship is actually work that was done using expensive material Materials and  onerous amounts of labor.  The work wasn’t done poorly to save materials or time, it was done poorly because the roofer didn’t know better.  No one’s perfect, but our company is significantly different.   We have been trained and educated on the technical fundamentals of building science and understand the procies of best practices.  Decisions are case by case and a makeshift approach can be significantly pragmatic in certain circumstances, but it’s beneficial to every building owner and stakeholder to chose a roofing contractor who cares about building conscientiously using knowledge as a guide.

Quality work of this type can make a big impact and positive difference. Investments into good quality construction have a positive return on investment and avoid the need for continued mitigation of unexpected or unplanned problems throughout the life of 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,  contact us or fill out the webform below and drop us a line.  We will be in touch if we can help.

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