A roof system generally includes several different types of materials and components. Often when people speak about a roof system they refer to the roof system by the type of roof membrane. However, the membrane itself is just one part of many parts which together make up a complete roof system.
The roof system will generally include terminations, transitions, underlayments, sealants, fasteners, flashings, and adhesives, and even insulation (which is part of the roof system and NOT the framing system.) Together this collection of varied elements make up a roof system.Each of these different categories and types of materials include several specific items used in each roof system. From a building science perspective, it’s much better to think about the roof system as a collection of several components with interconnections and dependencies which work together to create a roof.
Used In Flat or Low Slope Roof Systems
- Roof Rake boards happened to be used in both types of flat or low slope roof systems and high slope roof systems. (The slope is also referred to as the roof pitch.) Essentially, around the perimeter of a roof system, just below the roof membrane itself, there is a board to terminate and transition from wall to roof. On the horizontal areas of the roof, that board is generally referred to as a fascia board. At angled and rising areas such as above gable or gambrel walls, a similar board will be installed call it a rake board. The rake board is generally installed along the sides of a building, but not in all cases. The location of the rake boards depend on the facing of the building gable or end wall and there are even alternatives such as gambrel walls and other types of roof-wall system combinations.
Protecting The Subfascia
- One of the main purposes of rake boards, and fascia boards, alike is to protect the subfascia. The subfascia is actually part of the building frame, and although part of the building that transitions from the roof to the walls, it must be protected from the elements. Yet another purpose of trim boards such as facial and rake boards is to provide a substrate to mount or install water diversion systems such as guttering. Almost invariably, rake boards are installed with a metal or similar impermeable drip edge. The drip edge usually underlays the roof membrane and extends beyond the roof membrane to cover the top of trim boards,
In the image below the areas of the fascia board and the drip edge termination one termination on top of that fascia board are labeled for identification and clarity.
Fascia boards can be selected from several different types of material classes. We recommend talking to a contractor such as ourselves for advice and direction on the selection of materials, but overall there is no perfect material for exterior rake boards. Natural wood types are an option but natural wood is expensive and not lasting. Synthetic wood types are long lasting but they are not allowed to be installed in certain types of historic installations and also have lower cohesion rates to coatings such as paint and coatings. Synthetic boards also can deteriorate, warp, and twist at accelerated rates with exposure to sunlight. Cementitious boards are even an option but yet more expensive both in terms of labor and materials. All of these different considerations should be taken into account when choosing the materials for the project, but materials are perfect non-masonry exterior applications.
Maintaining Wood Trim To Last
From a conservation and preservation perspective, several approaches can be taken to improve conditions related to selecting, installing and maintaining exterior wood trim. Primarily, exterior wood elements should be inspected and checked on a routine maintenance schedule, either seasonally or at least annually. If coverings are kept in good condition, the life of exterior trim can be significantly extended. Hire a professional contractor which specializes, understands and appreciates historic construction elements and buildings.
In this article we talked about the following terminology and concepts, follow the links below for more related information from the IDS website:
- System, Roof
- Membrane, Roof
- Roof terminations
- Roof transitions
- Underlayments, Roof
- Building science
- Low slope, roofs
- High slope, roofs
- Pitch, roof
- Gable, roof or wall
- Gambrel, roof or wall
- Rake boards
- Water diversion
- Drip edge
- Natural wood
- Synthetic wood
- Cohesion coefficients
These concepts are part of the fundamentals of low-slope and flat roofing and pitch roofing and historic masonry building repair and restoration. .
The links in the list above will take you to other articles with more information on defects, failures, preservation and repair of historic masonry. You can learn a lot more on our blog. Feel free to check it out. If you have questions about the historic masonry 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.