Last week, we had the opportunity to take a look at the shell of an old block building that has been in disrepair for many years. Today we will look at a second part of that case study, as we look at additional visual aspects of the building which have implications in the structural and masonry construction. We pick up where we left off last week and we talk about corrugated metal roofs.
Metal roof deckingCorrugated metal roof decking is one of the most ubiquitous roofing materials in the world. It is strong, lightweight, and relatively durable in terms of corrosion resistance and or deterioration resistance from the elements. There are a relatively small handful of roofs in the Washington DC and Capitol Hill area which have standing seam or similar flat seam metal roofs, but they’re relatively rare and declining in proportion overall. Flat and standing seam roofs though are slightly different than corrugated metal roofs. Corrugated metal roofs have a degree of rigidity in the panel of each piece, due to the ridge-like angle of the corrugation. That corrugation provides rigidity because the opposing angles of the bent metal stiffen the sheet of metal from which each panel is made. Corrugated metal roofs are much less common in the Washington DC area. Once in a while, on very small roofs we will find them used where there the span of the roof is small enough that there are not many end seams. Seams in panels, like this, are susceptible to ice damming in relatively low slopes. Ice damming is a condition where water will build up and rise vertically in events of precipitation with temperatures hovering around 32° F for an extended period of time. In those particular conditions water will build up and rise upwards under a sheet of near frozen or semi-frozen materials on top. Moreover, standing seam roofs, with their sleek, uninterrupted surfaces, offer an aesthetic appeal that sets them apart from the more common corrugated counterparts. The decline in their proportion within the Washington DC and Capitol Hill area may be attributed to cost considerations, or advancements in roofing technologies favoring single-ply thermoset or polymer materials. Despite the decline in metal roof prevalence, in the DC area, metal roofs can still work in specific applications such as low front porches where the roof is in view from the ground. Some building designers might opt for metal roofs to achieve a contemporary look. The corrugated metal roof panels are secured on a purlin system, in this case the purlins are the smaller elements running the length of the building in resting upon the larger roof trusses which act similar to girders in Capitol Hill and Washington DC roof systems. Often, in our region, in a stick frame scenario, the girders are referred to as king joists because they are essentially built very similar to regular wood joist or rafters, just doubled or tripled for additional strength. Due to the untempered nature of the space below, there is no insulation underneath of the roof structure nor on top. By comparison, most buildings in the Washington DC and Capitol Hill region require a significant amount of insulation at the underside of the roof or at the top of the interior ceiling. Block Infill around the Truss EndsLast week, we looked at pictures of the structure of this building from several different angles. You may have noticed that there is a band of block around the top of the exterior walls which is different in color. That block was installed separately and after the majority of the block walls in the structure of the building. We speculate that the base building walls were built and as the trusses were manufactured to the specifications of the building, some time had passed between the installation of the walls and the installation of the roof trusses. During that time the supply chain availability may have changed and the original builder may have had to switch to this different block for the very top of the structural walls. Those structural walls though, all possibly equivalent in structural capacity throughout, are different at the very top. The block at the top two courses is set in place only to fill the gap and provide a type of roll blocking at each trust location. Essentially, the trusses are only bearing on top of the original block work and the infill block at the top then has no structural bearing of the roof placed upon it. Gable EndAlthough the slope of this roof is relatively low, the building is still built with Gable ends at the front and back. Gable roofs are one of the simplest layouts, a step up in complexity from a flat roof, they just have a center ridge, in most cases. The slope of this roof is around 2.5 to 12. That’s one of the lowest slopes to be considered a slope roof and not a flat roof. Lower than about that angle, a roof may be considered a flat roof. In most cases, flat roofs are not really flat, even though they’re called flat or often more accurately called low slope roofs, they must have some degree of angle or grade or slope to allow water to shed off of the roof itself passively, through gravity alone. At the top on the right hand side of the gable, to adjust for either a miscalculation or a change to accommodate the roof system, they extended the original beam. Generally, in most building layouts, the gable end and the associated gable wall actually has a lower structural load and therefore requires a lower structural capacity than the other walls of the building. In most simple layouts, the gable end is less wide than the walls which carry the eave of the roof system. Most of the weight and or bearing of roof trusses, or roof rafters rest upon the walls under the eave of the roof. Most stick frame buildings with gable roofs in the United States carry the roof rafters or roof trusses on the eaves, more than at the gable ends. Gable ends generally have a rake board that runs underneath of the roof to terminate the wall at the Gable end of the building, and that wall carries much less of the roof load then the perpendicular opposite walls of the building. Unstruck Mortar JointsStriking a mortar joint involves using a joiner tool to shape and refine the mortar joint, transforming it from a raw extrusion to a precisely contoured form against the masonry. This meticulous process plays a crucial role in enhancing the aesthetics and structural integrity of brickwork. In Washington DC, the practice varies across historic and modern constructions, with distinct mortar joint types prevalent in different architectural contexts. Flush struck joints, commonly observed in historic common brick structures of Washington DC, feature mortar in plain with or close to the brick face. This process imparts a clean and uniform appearance, reflecting the historic charm of the buildings. Conversely, modern brickwork in the region often is built with concave joint striking. Using a concave jointer tool, this method creates a slight radius indentation in the mortar, adding a contemporary touch while also serving functional purposes. Beyond flush and concave joints, other common types include weather struck joints. These joints involve shaping the mortar at a slight angle, preventing water from pooling at the edge of the brick and enhancing durability against weathering. This detail in joint striking serves as a protective measure, addressing concerns about moisture infiltration and potential damage. The rationale behind joint striking extends beyond aesthetics; it encompasses practical aspects like compaction. By striking the joints, the mortar is compacted, ensuring a denser, more durable outer structure. This compaction contributes to the overall longevity of the masonry, strengthening it against external elements. In the case of this particular building, the joints have not been struck, they are almost raw and similar to a flush strike but never smoothed or compacted at the surface of the face of the block or masonry. In this particular case, unlike historic buildings in Capitol Hill and the historic neighborhoods of Washington dc, the masonry joints have not been struck because the final finish of the wall was intended to not leave the block work exposed. They were planning to install a stucco or parce coat type finish on the walls. Concrete Subfloor Intentionally Built Extra LowMany people might walk right past these steps and not notice that the treads at the stairway have all been built a little bit lower than the top stair riser. This isn’t just an omission or mistake, it was done intentionally. In the plan for construction, the builder intended to apply a slab on top of the ground and on top of each of the treads. The slab at the treads would have likely been decorative and each riser would have been increased about 2 in. There are some commonly adopted building codes in the United States, but almost each municipality throughout the country has a right to adopt their own building code. In most cases though the building code requires a minimum and a maximum riser and only about 3/8 of inch total deviation throughout the highest and lowest stair riser within the entirety of the staircase. Electrical EmbedsAfter the installation of the block work, if the electrical wiring or tubing or conduit for the electrical wiring is to be mounted on the face of the masonry then the finish such as stucco, furring strips and drywall, or some other type of wallboard then has to be framed out far enough away from the wall so that it can accommodate the space of the electrical conduit. Otherwise, electrical wiring and conduit must be installed on the face of the finished wall which generally looks very unprofessional and /or similar to a utility grade finish. In this particular type of building assembly, it saves cost and looks much better to run the electrical wiring inside of the space of the block work. Historic masonry upkeep and preservationTo properly maintain, repair, and care for these historic buildings, a knowledge, interest and understanding of historic building principles is required. Here in Washington DC, historic masonry buildings are extremely expensive and the amount of financial loss caused by improper repointing and low quality construction is staggering. However, in addition to the direct financial value of the property, there is also a cultural loss when historic buildings are damaged. By comparison, consider neighboring poor cities, when historic buildings are damaged, it’s not just the loss of value to the property owner, there’s also a loss to all inhabitants and visitors of a city, present and future, who care about architecture, history, and culture. We encourage all of our clients, and all readers of this article and to our blog in general, to prioritize the historic built environment of Washington DC and neighborhoods such as Capitol Hill, Dupont Circle, and Georgetown and become educated on on the difference between proper historic preservation versus improper work which leads to significant damage to the historic fabric of a building. From a conservation and preservation perspective, several approaches can be taken to improve conditions related to deteriorated historic brick masonry. Primarily, lime mortar brick joints and low temperature fired soft red clay bricks should be inspected and checked on a routine maintenance schedule, either seasonally or at least annually. If brick masonry is kept in good condition, the life of embedded wood elements can be significantly extended. Hire a professional contractor which specializes, understands and appreciates historic construction elements and buildings. 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, contact us or fill out the webform below and drop us a line. We will be in touch if we can help. <p>The post Case Study of a Large Block Masonry Building Shell – Part II of II first appeared on Infinity Design Solutions.</p> Via https://www.ids-dmv.com/masonry/case-study-of-a-large-block-masonry-building-shell-part-ii-of-ii/
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About UsInfinity Design Solutions LLC (IDS) is a full service general contracting company in the heart of the Dupont Circle neighborhood of Washington, DC. We focus on repair and renovation of buildings and facilities in both historic designated neighborhoods and the commercial-zoned central business district of the city. Follow Us
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