Constructing buildings is serious business. It takes a lot more than just wood, steel, glass, bricks and concrete. There is a lot of math and countless structural components that go into constructing a sound building that is both functional and safe for use. When constructing a municipal building it helps to consider the property itself. Not only is the property size important to the building project, but also the grading of the property.
One of the more iconic images that may come to mind when you think about buildings built on a slope is the winding streets of San Francisco lined with beautiful architecture. As picturesque as these scenes are, there are a lot of engineering feats at work here. The slope of a property can mean quite a few different things. For instance, issues with flooding tend to be dramatically reduced, but landscaping and mobility may pose a few engineering hurdles.
Because municipal buildings tend to be larger and heavier than some other types of buildings, an engineering firm should be hired to handle all of the technicalities that come along with building a strong and functional structure on a slope. Whether it is buildings for public use, religious buildings, schools or law enforcement facilities, there is a lot of scheduling, permits, inspections and municipal specific regulations that are necessary. That is why it is in your best interest to hire a construction team that is knowledgeable and experienced.
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Advantages of Building on a Slope
One of the biggest advantages of building on a hill is the view. By building atop a slope, you get a bird’s eye view of everything that is at the bottom of the hill. Hilltop buildings also tend to have a more commanding presence. This may be a very desirable characteristic of a municipal building. It can make the building stand out so that it is easy for residents to find, and it can reinforce the importance of the building’s role or what takes place inside the building.
Because there are fewer buildings to obstruct the sunlight, many structures built on slopes get a lot of natural light. This is helpful when it comes to the building’s energy costs and consumption. Orienting the building in the right direction to optimize the amount of natural light can also maximize the light that being on the slope already provides. Lower levels will also experience better lighting than that of property on level land.
Disadvantages of Building on a Slope
The main disadvantage of placing a municipal building on a slope is making it accessible for the residents and employees who come to the facility. You will need to take into consideration handicap access ramps and their placement, grade of slope and their length. You may also have to arrange the parking lot in a way that allows those with special mobility needs to easily access the building. It is important that the building be ADA (Americans with Disabilities Act) compliant. If stairs will be necessary, you’ll want to decide how many and how long will each thread be.
Another disadvantage that building on slope brings is landscaping. If there will be grassy areas, they will be more difficult to mow or landscape. Whatever groundskeeping company is used will undoubtedly factor in the grade of the property when making their bid. The steeper the slope, the more difficult and dangerous the mowing will be.
Why Slope is Important
A property’s slope will impact the way a structure is built. It will be a determining factor in the foundation wall heights, the fill and grade quantities, as well as other parts of the construction process. Usually, a professional land surveyor will survey the land to determine the boundaries of the property, the proposed building and the slope of the property. The surveyors will place slope stakes to determine the point where the slope intercepts the natural ground, the slope catch or catch point.
Slope staking can be done manually, with tape, a rod and a level; conventionally, with the offset and the design catches; modified convention method, which combines a manual and computerized approach; or by GPS/RTK, which uses a digital terrain model to quickly calculate the catch point so the surveyor can walk straight to it and stake it.
Ascending vs. Descending Slopes
Ascending slopes and descending slopes have slightly different building needs and requirements, such as setbacks and clearances. When a building is built near an ascending slope, it helps for it to be clear of the slope good ways (the precise distance is usually specified by the municipality). Another safety precaution is to have a retaining wall built at the toe of the slope to prevent erosion and shallow failures.
When building on descending slopes, it is necessary for the foundation to be set in firm material that has an embedment. It also should be set back far enough from the slope surface for lateral and vertical support of the foundation without detrimental settlement.
When a site is graded, it is advised to have the top of the exterior foundation to be higher than the street gutter or the inlet of a drainage device. This helps to reduce the likelihood of flooding and it may solve some issues surrounding groundwater and the water table.
Slopes come with a particular set of environmental factors to consider. One of the more obvious factors is landslides. Depending on an area’s geologic composition, it may be more or less prone to landslides. Landslides are typically caused by slope instability. When gravity overcomes friction, a landslide can occur. Quite often water or shifting geologic material will trigger a landslide. Make sure you have a proper and professional geologic/engineering survey done on a site that is sloped.
Erosion is another concern when building on a slope. The steeper the slope, the more inevitable it is that there will be some measure of erosion. Erosion can take a large toll on the environment and can increase the risk of a landslide occurring. The sedimentation that is a result of erosion can damage drainage systems, alter the ecology of local waterways and cause the flora and fauna to begin changing.
Flooding must also be a thought. Buildings on slopes leave those structures open to increased flooding. The slope will create a faster runoff that is denser than on more level land. Buildings on the lower end of slopes and directly under them are particularly susceptible and may experience more frequent issues with flooding and standing water.
Cut and Fill
When a building’s construction involves a slope, it is common for some levelling to occur. Steeper slopes typically use a practice called cut and fill to fill in the land below. The process cuts rock and soil from higher slopes and uses that to fill in the land below. An important part of the process that cannot be ignored is shoring up both the cut and the fill banks to help control soil erosion and to maintain the building site’s stability.
The final stage of the cut and fill process is to plant vegetation that will help bind and solidify the soil there. When it is possible, it is a good idea to try to preserve the trees and plants that were already on the property. Every state has a Soil and Conservation District or Commission that you can bring onto your building project to help you evaluate the safety and stability of your sloped building site.
Because this is a municipal building project and it will experience regular public use, it is very important that the building and it’s stability be up to code. Anything you do that goes above and beyond what the municipality requires will be a feather in the buildings proverbial cap. The issue of safety should be paramount.
Because building on a slope comes with a completely different set of challenges than do other works sites, it is imperative to have experienced professionals on your team so that you won’t be looking at slope failure on the property in the future. Whether you’re working with a man-made slope or a natural slope, it is important to set out your plan of action prior to tackling the task to avoid slope failure. Slope failure can be a landslide, mud or earthflow or another mass wasting event. Slope failures are not always catastrophic with fatalities, but they are almost always very costly. Not only do slope failures cost a lot of money, but they also cost a significant amount of time.
When you have the right team and quality consultants working with you and your building project, you are greatly reducing the chances of experiencing slope failure. It is well worth the costs on the front end than to have to answer for avoidable mistakes after an unfortunate incident occurs. When you have team members on the job who aren’t knowledgeable about building on slopes are unsupervised or the supervision is inexperienced in this area, shortcomings are bound to exist.
Constructing municipal buildings on a slope require a few extra pieces to the puzzle, but the right professional and experienced team can take on this engineering feat and build a municipal building that will serve its community well for many years.