Read More On Fake Parapets In This Part II of The Series
Last week, we opened the first part of a three part series, looking at parpets, the requirements and benefits of rooftop parapets and this week continue by looking at the related building code requirements.
The outline of this series of articles follows:
- Purpose of a parapet
- Building code requirements
- Implications of property lines (and rights)
- Fire separation
- Joining disparate roof materials
- Better / best practices: dimensions, continuity, combustibility, durability, structural capacity
We pick up in section two of this outline.
Building code requirements
The 2018 International building code says the following related to parapets:
- “705.11 Parapets.
- Parapets shall be provided on exterior walls of buildings.
- Exceptions: A parapet need not be provided on an exterior wall where any of the following conditions exist:
- The wall is not required to be fire-resistance rated in accordance with Table 602 because of fire separation distance.
- The building has an area of not more than 1,000 square feet (93 m2) on any floor.
- Walls that terminate at roofs of not less than 2-hour fire-resistance-rated construction or where the roof, including the deck or slab and supporting construction, is constructed entirely of noncombustible materials.
- One-hour fire-resistance-rated exterior walls that terminate at the underside of the roof sheathing, deck or slab, provided that:
- Where the roof/ceiling framing elements are parallel to the walls, such framing and elements supporting such framing shall not be of less than 1-hour fire-resistance-rated construction for a width of 4 feet (1220 mm) for Groups R and U and 10 feet (3048 mm) for other occupancies, measured from the interior side of the wall.
- Where roof/ceiling framing elements are not parallel to the wall, the entire span of such framing and elements supporting such framing shall not be of less than 1-hour fire-resistance-rated construction.
- Openings in the roof shall not be located within 5 feet (1524 mm) of the 1-hour fire-resistance-rated exterior wall for Groups R and U and 10 feet (3048 mm) for other occupancies, measured from the interior side of the wall.
- The entire building shall be provided with not less than a Class B roof covering.
- In Groups R-2 and R-3 where the entire building is provided with a Class C roof covering, the exterior wall shall be permitted to terminate at the underside of the roof sheathing or deck in Types III, IV and V construction, provided that one or both of the following criteria is met:
- The roof sheathing or deck is constructed of approved noncombustible materials or of fire-retardant-treated wood for a distance of 4 feet (1220 mm).
- The roof is protected with 0.625-inch (16 mm) Type X gypsum board directly beneath the underside of the roof sheathing or deck, supported by not less than nominal 2-inch (51 mm) ledgers attached to the sides of the roof framing members for a minimum distance of 4 feet (1220 mm).
- Where the wall is permitted to have not less than 25 percent of the exterior wall areas containing unprotected openings based on fire separation distance as determined in accordance with Section 705.8.
- Parapet construction – Parapets shall have the same fire-resistance rating as that required for the supporting wall, and on any side adjacent to a roof surface, shall have noncombustible faces for the uppermost 18 inches (457 mm), including counterflashing and coping materials. The height of the parapet shall be not less than 30 inches (762 mm) above the point where the roof surface and the wall intersect. Where the roof slopes toward a parapet at a slope greater than two units vertical in 12 units horizontal (16.7-percent slope), the parapet shall extend to the same height as any portion of the roof within a fire separation distance where protection of wall openings is required, but the height shall be not less than 30 inches (762 mm).“
Interestingly, this particular row buildings, seems to hardly follow any of those requirements. But the word ‘follow’ is critical in understanding the context and history of how and why these buildings were built this particular way, without parapets extending above the rooftop. These buildings were not built to follow the building code, in fact, these buildings were built before the building code was even established as a governing authority.
The following discussion provides some explanation commentary, definition, and further description of some of the code requirements on roofing and structure, as related to roofing and parapet walls.
The first exception says that walls are required to have parapets if they are not required to be fire rated. Exterior walls, within less than 5′ adjacent properties or property lines are generally not required to be fire rated in several types of rowhome configurations, this would mean that in some cases exterior walls are not required to have a parapet, for compliance.
The second exception allows buildings with no floors greater than 1,000 ft² to not require parapets. It’s somewhat common that buildings in Capitol Hill or other parts of Washington DC, in rowhomes have all floors of the building, each less than 1,000 ft². In fact, most rohomes are generally just below 1,000 ft² per floor level. Some of the larger rowhomes in Capitol Hill and Washington DC are slightly larger than 1,000 ft² per level but it’s rare to have buildings with much larger square foot area’s per floor level in the CBD and/or associated surrounding neighborhoods around the center of the historic city.
These exceptions mean that exterior walls are not necessarily required to have parapets in all locations. The rear termination of a roof is a common example of an exterior wall without a parapet, this is entirely intentional in a typical Washington DC rowhome. Generally the other walls of the building, including the demising walls at the side where the buildings join the front walls will have a parapet but the rear of the buildings Generally have no parapet at all in fact they are often meant to be the lowest part of the roof system so that water can drain from the front of the building roof to the back. This slope to the rear is common, but exceptions may include internal roof drains which allow water to drain to interior parts of the building through dome strainers and channeled through piping that runs through the building, in most cases to below slab or below grade combination storm-sewer drain pipes. Outside of Washington DC, just as a side note, it’s relatively uncommon for commercial buildings to have combined storm sewer and sanitary sewer drains. The combination of these drain systems is a relic of the historic construction of Washington DC.
The next 2 pictures below show the same applied or fake parapet from different angles.
The rooftop on the right side of the picture below is covered with an EPDM type membrane. The roof on the left side of the photograph is similar to modified bitumen. It’s a torch down type application but bleed out is relatively minimal which indicates it could be a different system or an APP type modified bitumen membrane which was poorly installed. The modified bitumen membranes should be either topped with a ceramic granule covering to protect the membrane from exposure to ultraviolet rays over time or the membrane should be coated with a liquid applied coating to give a similar type of protection.
A liquid applied type coating requires quite a bit of work over the life cycle of the roof system. The most durable type coatings are siliconized or silicone based, but those types of coatings while they last much longer are a one-way type of application, meaning that once silicone is applied, no other types of coatings can be applied. By comparison though if an aluminum coat is first applied, an elastomeric or a water based type coating can later be applied on top or in successive reapplications in the future, even silicone can be applied on top of a water based type application, but it cannot be applied in the reverse order. Also, while silicone lasts much longer than water base type applications, it is much more expensive so the pros and cons of the trade off have to be weighed on an individual basis.
Implications of property lines (and rights)
When you look across the face of a row of buildings, it isn’t exactly easy to determine, in most cases, exactly where one building ends and another building begins. In fact often professional painters will slightly mistake the location of the property line and paint a little bit further on to the adjoining neighborhood property across the property line. The easiest way to determine exactly where the property line lies between front yards and backyards and the vertical faces of buildings is to look at the rooftop parapet. That rooftop parapet, in almost all cases, is split exactly on the property line. There are some assumptions built into that statement.If the property line has changed from the time of original construction then there might be variations or exceptions, and if the original contractors misunderstood the survey and layout they could have built the demising wall off the property line, but by-and-large once the demising wall has been built, there is no changing access to the sides of the demising wall. You can never trust the layout of a fake parapet though, unless you go back and use invasive destructive demolition to confirm the layout of the interior demising wall.
The rooftop parapet service extra purpose of indicating the property line between properties, but if the parapet isn’t there it makes it complicated, not just in being able to identify and having the knowledge of where the property line may lay, but also in separating the elements of the building from one another across the property line. The coping is almost always shared, between attached buildings. So in other words even though only one of the building owners, in side-by-side properties, generally the most recent re-roof pays for the coping. that coping helps both buildings because it protects the parapet wall. And the brick of a structural demising wall, is generally continuously brick from top to bottom. That brick is a shared element because it can’t really be dismantled without affecting neighbors on both sides of the property line. But the one of the benefits of the parapet is that it allows a neighbor on one side of the parapet to completely separate the remainder of the roof system from the neighboring properties on the other side of the proper line. That way, and owner can make decisions that affect the life cycle planning of the building and the associated expenses. For example, when one owner replaces their roof, they might chose to go with a good roof system that can last for decades, but the neighbor might not be in a financial position to make that type of long term investment. Because of the parapet wall, one roof can be dismantled and replaced without affecting the neighbors roof.
When 2 neighbors or more have to make decisions about protecting their real estate investments, at the same time together, it could become extremely complicated. So the parapet provides an amazing benefit of being able to isolate and separate rooftops from one another between neighbors.
We talked about how demising walls are generally made, and historic brick buildings in Washington DC, with a double wythe of solid brick. That brick is not combustible. In fact, bricks are made from clay that had been fired in a kiln, so you could say that fire creates bricks. It doesn’t really destroy them. (Technically, there is a temperature point which will cause non-refractory bricks to crack and / or spall and fail, however building fires generally do not reach temperatures quite that high.) By-and-large though, the common bricks used in demising wall construction are considered fireproof or significantly fire resistant.
Joining disparate roof materials
Five of the Materials most commonly used for low-slope roof systems follow:
- TPO (Thermopolyolefin)
- Modified bitumen
- Standing seam metal
- Ballasted BUR (Built-up roof)
Within the list of the top 5 types of roof membrane materials, there are variations and subtypes that could also be selected and used. between these different types of materials, there are generally problems with connection and/or adhesion from one membrane type to the next.
Each individual roof may be completed by different installers or contractors and may be selected by each individual building or homeowner depending on their options as they choose based on cost and longevity and level of required maintenance. Each of these different types of roofs have different costs and different durability and longevity and require different levels of maintenance throughout the life cycle of each system. People make these decisions based on their investment horizon, their timeline of planning for building ownership, and/or plans for potentially selling their property in the future or changing the use of the property.
If each individual owner makes a rooftop material selection based on differing criteria, they will not all have the same type of membrane and they will therein have compatibility problems when joining from one rooftop to the next. However, on a roof system, between multiple buildings without parapets, the individual roof membranes have no method of termination except for from one to the next except when an applied or fake parapet is built. Even though the word fake sounds very bad, in this case it’s better to have built a fake or applied parapet than have no parapet at all.
Better / best practices: dimensions, continuity, combustibility, durability, structural capacity
This applied parapet, installed on each side of the EPDM rooftop covering shown below, looks very similar to a real continuous parapet, but there are some immediately observable differences and there are also some significant differences under the surface:
- Structural capacity
There’s a few signs that indicate, right off the bat, that these parapets are not real parapets. They work, functionally, to terminate the rooftop membrane, but they do not run continuously down to the structural demising wall, and they do not create a complete fire stop to the code requirements of modern construction. This may not be a specific breach of code requirements because many existing details circumstances of historic buildings are accepted under what’s considered a grandfather condition.
The dimensions of this new parapet are approximately 2.5″ in with at the top coping. Almost 3″, at the drip edge projections on each side of the applied parapet. An original, historic and functional brick parapet would be an extension of the substrate demising wall below and would have dimensions of approximately 9 to 11″, from outside to outside of the top of the aluminum coping.
The biggest functional difference between a real and applied or fake parapet is that the real parapet runs continuously and not only can provide a complete fire break between buildings, but for installation of HVAC systems or other rooftop equipment, I-beams are commonly placed on top of structural parapets. I-beams or equipment could not bear on the applied parapet, not only would the applied parapet not have the needed strength, but it may also create pressure points which could lead to punch through at the framing below the rooftop deck.
A fake or applied parapet, although useful in helping terminate between differing material classifications or types of roof materials, has near no benefit in stopping or preventing fires from jumping from one roof to the next and therefore will not help with fire separation. Fake or applied parapets are also built with framing materials, unlike historic original parapets which are built with a double wythe historic brick masonry construction. Framing materials are almost always highly combustible. One particular exception is lumber that has been pressure-impregnated chemically treated to resist combustibility. This type of lumber is often referred to as FRTW which stands for fire retardant treated wood. Because of the extremely high cost, the use of this lumber is rare and little to no regulatory overnight is provided by AHJ’s such as DCRA. For these reasons, there are impediments in the local construction industry that deter or prevent this issue from being corrected or ameliorated.
Durability and Structural capacity
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, lacking in longevity, poor quality or poor workmanship is actually work that was done using expensive 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 principles 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 choose 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.
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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.