C&R-2
281 Calhoun Street HP 8030 / HSPV 803 Assignment #3 By: Amber Anderson, Shannon Devlin & Jacqueline Don
Page 17
Page 1
C&R-2
Report Contents: Report Contents: Description of Building Systems..........3 Diagram of Building Systems................7 Description of Building Systems..........3 Conditions: Annotated Images.............9 Diagram of Building Systems................7 Conditions: Deterioration Glossary...12 Conditions: Annotated Images.............9 Building Pathology...............................17 Conditions: Deterioration Glossary...12 Bibliography..........................................22 Building Pathology...............................17 Bibliography..........................................22
Page 2 Page 18
Page 2
C&R-2
Diagram of Building Systems
Page 7 Page 19
C&R-2
Single-ply roof membrane
Roof: Site-cast concrete slab decking
HVAC (?): Inconclusive information available
Steel truss frame
Typical windows: curtain wall with aluminum frame
Typical door: solid core metal
Foundation: slab on grade
Site-cast concrete structural body
Typical wall: site-cast concrete Page 8
Page 20
C&R-2
Building Pathology Building Pathology
Page 17 Page 21
Page 17
C&R-2 Built in 1974, 281 Calhoun Street is only fourty years old –a rarity by Charleston, South Carolina, standards. The building systems and materials discussed in the “Description of Building Systems” section, however, have fared relatively well over the last fourty years. Expected mechanisms of decay are affecting the materials which have an understood shorter life span, like sealants, while the more durable product of concrete has only minor defects. The following discussion of this building’s pathology in relation to the conditions outlined in the previous sections will take a top down approach –meaning that it will begin with the roof and follow the flow of gravity and/or water down through the foundation and into the soil below. Though access to the roof of 281 Calhoun is limited to blurry aerial images, there is a noticeable amount of dark discoloration near its east and west edges (05.01.01). This discoloration is likely the product of water damage in the form of staining and biogrowth. Both of these issues are created by the concentration of water and debris on the surface of the roof. Water is a particular problem on the roof of 281 Calhoun for a number of reasons, including: its low slope, parapets, and numerous penetrations through the single-ply membrane. Low-sloped roofs are notorious for problems with ponding water. Ponding can begin immediately from defects in the construction process, such as a slope shallower than 1:48 or insufficient drainage facilities, or over time with the eventual breakdown of the roofing materials. In either case, concentrations of water on the surface of the roof will lead to exponential growth in the deterioration process. As more water collects, the roofing materials deteriorate faster and allow even more water to flow to the area. This becomes a problem when the roofing membrane can no longer efficiently keep water outside of the building assembly. A plethora of aesthetic and structural concerns begin to surface with the onset of water leakage into any area of the building. 281 Calhoun’s roof also allows water to collect by way of its parapets and roof-penetrating elements. As both the outer edge of the roof and the projecting central column contain parapets, there are numerous locations which encourage the concentration of water. In condition 05.01.01, the highest levels of discoloration are noticeable at these locations –especially where the two parapets meet on the east and west sides near the central column. When a parapet projects upward from a low-sloped roof it creates a barrier which blocks water from running off the edge of the building. Although parapets have positive aesthetic and functional qualities, it is important that careful attention is paid to their waterproofing details. The major cause of concern in relation to 281 Calhoun is the condition of flashing at the parapet-to-roof detail. To direct the flow of water from the top of the parapet down the slope of the roof and towards appropriate drainage flashing needs to provide adequate coverage over the joint between the two planes. This flashing needs to contain both an adequate upstand and downstand in order to prevent water from flowing behind or underneath of it. Ideally the upstand of the flashing will be tied into the parapet wall to further prevent water flow. In other building types this can be done in the form of through-wall flashing or by lapping a row of weatherboard over the flashing. If the presence, condition, and assembly of the flashing at 281 Calhoun is allowing water to access the parapet-to-roof junction this creates a prime environment for deterioration. If the roof simply lacks flashing this could mean that water is entering the building through this junction. While this is obviously problematic it would also mean that water would have the potential to evaporate on its own during normal wetting periods. However, if there is flashing that is not doing its job adequately this could trap unwanted water for longer periods. Dislodged or improperly applied flashing creates an impermeable layer which prevents any moisture from evaporating in a timely manner. It also creates a trap for any debris. These factors will inevitably accelerate the deterioration process. Additionally, while elements which penetrate the roof membrane need flashing similarly to parapets, the flashing details and functions are not exactly the same. In the case of ventilation pipes, flashing details can become rather tricky. Designing effective flashing involves precise geometry in Page 18 Page 22
C&R-2 order to protect all sides of the penetrating element. This detail is particularly important as well as the penetration essentially creates a hole in the roof and a direct line of access into the building assembly. Leaks associated with improperly flashed roof penetrations also tend to prove difficult to correct. The actual source is often difficult to determine as water tends to move in unpredictable ways once inside of the roofing system. Noticeable water staining in a certain location on the top story’s ceiling does not necessarily indicate that the leak is directly above this location. Roof leaks often translate into semi-destructive investigation work. Though access was not granted to the inside of 281 Calhoun, inspection of the interior ceiling should be conducted. If any leaks have manifested in the ceiling itself, further investigation needs to be undertaken to determine the source. Additional investigation should be conducted on the roof itself to determine whether or not the discoloration seen in aerial images is representative of the potential larger problems described above. Just below the roof, on top of the steel truss frame, runs a narrow band of metal (likely steel) which is badly corroding (02.04.01). While there are some instances of corrosion on the adjacent steel, this is the area of highest deterioration. This is likely due to this band’s exposure to the elements. Sitting at the top of the wall, this band receives the brunt of water, wind uplift, and ulta-violet damage. The location of this band means that water from the top of the wall runs directly onto it. This constant first contact with water has translated into an accelerated process of corrosion. The material has oxidized and is flaking. Wind uplift and ultra-violet rays are also likely causing stress in this area. While ultra-violet rays result in the faster breakdown of material, wind likely causes an uplift force on this topmost piece of metal. The combination of these factors puts extra stress on the metal and inevitably causes the rate of corrosion to increase. Left unattended this material will continue to deteriorate and likely direct more water into the adjacent steel frame. The area could potentially be cleaned of oxidation with a wire-brush and primed with a corrosion-inhibitor. It is important to note that the inhibitor should be applied to the cleaned steel immediately following wire-brushing as this leaves it extremely vulnerable to environmental decay mechanisms. Following this application paint would help to protect the area from further corrosion.1 281 Calhoun’s steel truss frame appears to be in relatively good condition. Minor corrosion is evident in expected areas. For example, the lower southwestern corner (02.01.02) shows mild signs of oxidation. As this is the last location that water can run down the outside of the frame before the return to the concrete core below, it makes sense that water would flow and collect in this area. Corrosion is also predominate above minor projections in the steel, such as in this example, which allows for additional water collection. This exposed location is also likely more susceptible to driving rain than other locations. The mineral-laden marine environment in Charleston also likely contributes to any corrosion found on the building. However, in this location the problem is only in its initial stages. Mild discoloration has begun from oxidation but no layers of oxidized material have begun to flake. Brushing these areas of the minimal oxidation, priming them with a corrosion-inhibitor, and painting them would likely halt any deterioration currently taking place. Typically when addressing corrosion mechanisms it is ideal to address the source of the water as well. However, the nature of this system would not easily allow this to take place without visually intrusive measures. In this particular situation cyclical maintenance is preferred. The steel also shows signs of improper cleaning techniques (02.01.03). When undertaking maintenance work it is important to choose the appropriate products and tools. The work done in this location likely made use of a wire-brush or similarly abrasive tool. An inappropriate chemical, such as bleach, may also have been used liberally. Abrasive cleaning was likely unnecessary in this location and 1. Sharon C. Park, FAIA, “Preservation Brief 13: The Repair and Thermal Upgrading of Historic Steel Windows..” Technical Preservation Services. National Park Service. Accessed electronically on December 1, 2014: http://www.nps.gov/tps/how-topreserve/briefs/13-steel-windows.htm
Page 19
Page 23
C&R-2 will contribute to the breakdown of the steel. The steel appears to be scratched as a result of the abrasion and is thus more susceptible to corrosion. In order to mitigate the effects of this abrasive cleaning the surface should be gently cleaned, primed, and painted. Though some of the original material is likely gone, this process will help to protect what is still there. In future cleaning cycles a nylon-bristle brush and mild soap should be used. The aluminum-framed curtain wall windows on the second floor of 281 Calhoun appear to be in excellent shape. Though some minor discoloration has taken place over the last fourty years, there is less than would be expected (02.02.01). The aluminum-framed drive-up window on the first floor is in similar condition. This is likely attributable to the lack of exposure to both of these systems have. On the second floor the windows set back from the steel truss frame about a foot, while the first floor window is completely covered by one of the cantilevers. Though the second floor curtain wall may endure some rain and window loads, they are likely minimal. The mild discoloration in some areas is probably due to air pollutants as the building is placed on a busy street corner. On the second floor only one mechanical issue was spotted. A small strip of gasket on the eastern side of the building has come loose from a window section. This is to be expected due to the building’s age and would likely have been fixed if the building were still occupied. On the first floor of 281 Calhoun a window air conditioning unit has been placed in one of the driveup window openings (see right). This unit is in poor shape likely due to deferred maintenance. There is demonstrable soiling and corrosion throughout. A metal strip appears to have been fastened to the wall below the unit, perhaps for support, which has become loose and badly corroded. This corrosion and subsequent breakage are likely due to water leakage from the unit itself. A modern PVC pipe has been installed near this metal strip indicating that the unit had a recurring problem with water leakage. If this building were to be reoccupied in the future the need for this unit would have to be investigated. Perhaps an insufficiency with other existing HVAC would need to be addressed. Regardless Deteriorated air conditioning unit. of the interior conditions, this unit should be removed and replaced if necessary. It is evident that it is not functioning properly due to the mechanical nature and limited expected life span of these systems. Additionally, the current pipe is directing water into a problem area of the building’s foundation discussed below. In general, the concrete body of this building is in good condition. There are a few areas of expected soiling (01.02.02) and minimal spalling and delamination (01.02.01 and 01.02.03). The soiling is typical of high traffic areas and is likely only an aesthetic issue. This could be left as is or gently cleaned. The spalling is so infrequent that it does not appear to be indicative of any larger issues. It is likely the result of mechanical abrasion. If over time water begins entering a this location it should probably be patched. The delamination of concrete (01.02.01) near the base of the building is near plant growth. These two factors likely indicate that water collects in this area. As Charleston floods regularly this is likely the case. While this issue has not progressed to a serious condition it should be monitored regularly to determine whether or not it is actively deteriorating or was the product of certain nonrecurring conditions. If more of the aggregate becomes exposed a concrete patch should be undertaken to protect Page 20 Page 24
C&R-2 the wall and foundation from additional water entry. In a larger scope, the grade of the adjacent ground should ideally be altered so that water runs away from the building. As it currently stands, asphalt runs right up to the surface of the wall, thus preventing proper draining. An induced slope could mitigate these effects. The most disruptive and potentially serious of 281 Calhoun’s conditions is the settling or upheaval of the extended concrete base on the north side of the building (01.01.01 and see right). This small slab was clearly poured separately from the rest of the building, but appears to have been level in previous years. This is made evident by the fact that some type of sealant was used to fill the subsequent separation from the rest of the building. These sealants have fared poorly over time and are now failing (03.02.02). This is to be expected of caulkings and sealants, though, as their composition only enables them to be effective for a short period of time.2 The sealant failure is by no means the cause of the concrete in question’s differential settlement. However, the lack of effective cover is likely allowing additional water entry which is in turn exacerbating any problems below. The cause of this concrete slab’s differential Differential settlement of extended slab portion. settlement could be a number of things. As this material was clearly added in a different pour than the rest of the building, it could have been a later addition. This means that this slab may not have the same type of footings, properly located footings, or any footings at all. The lack of applied support below this slab may have resulted in sinking of the portion furthest from the rest of the building -which is sufficiently supported. There may also be a lack of ties from this slab into the rest of the building. Rebar would help keep this additional slab level if tied into the main structure. Another potential cause could be problems with the soil below the building. If the soil was improperly excavated there may be softer and harder spots. There may also have been improper backfill once the foundation was poured, leading to uneven soil depths around the building. Depending on the moisture content of the soil, which is likely high given its location, there could also be uplift forces driving the portion of the slab closest to the building in an upwards motion. Uplift forces can be caused by inadequate drainage characteristics of the soil below such as the presence of fine grain silts and clays. Regardless of the cause, this condition needs to be monitored to determine whether or not the movement is active or inactive. Though it does not seem to be causing any problems with the main building itself, the underlying causes may eventually threaten the structural stability of the building. Investigative work, such as the use of ground penetrating radar, might be informative but would require large amounts of time and money. The severity of the problem does not currently seem to indicate the necessity for these measures. 2. Sharon C. Park, FAIA, “Preservation Brief 47: Maintaining the Exterior of Small and Medium Size Historic Buildings.” Technical Preservation Services. National Park Service. Accessed electronically on December 1, 2014: http://www.nps.gov/tps/ how-to-preserve/briefs/47-maintaining-exteriors.htm
Page 21
Page 25