Insights from Site-Structural Desk Studies for Urban Construction

The planning for a construction project in the urban environment is typically more complicated than in other areas. With greater density of construction comes traffic congestion, buildings and other structures in close proximity to the work and increased subsurface risk from utilities, underground structures and past land use. In addition, site-related factors can constrain design and construction options, or at least render certain options less feasible. As a result, construction is typically costlier and often more hazardous. This additional construction cost and risk can expose project investors and developers to considerable financial risk.

Stakeholder due diligence should reflect the risks and rewards of a project. Given the high costs, complexity and risk of urban construction, it is necessary to understand the cost- and risk-drivers underlying project feasibility. The best time to determine feasibility and devise strategies to control cost and manage risk is the pre-design phase. At this early stage, the project may be in the process of being studied as an investment, perhaps with aid of concepts developed by an architect. This precedes the ‘point of no return’ when few resources have been committed and few irreversible design decisions have been made.

Desk studies represent a low-cost approach to due diligence for evaluating site-related construction considerations in advance of more intensive investigations. A desk study usually consists of a review of information about a site from the owner, public sources, and sometimes other parties. Continue reading “Insights from Site-Structural Desk Studies for Urban Construction”

Five Construction Considerations for Urban Projects

Building in the urban environment is more complicated than in other settings. Consequently, it is important to think about construction considerations from project inception and, in some cases, coordinate the design with the realities of working on an urban site rather than the other way around. Five common construction considerations that should be considered by owners, design professionals and constructors alike are the implications of lot-line structures, elevated subsurface risks, foundation selection, excavation methods and monitoring.

Lot-Line Structures

To make the most use of sparse land, in dense urban areas, buildings are commonly built up to, the property lines on one or more sides. As a result, buildings may be practically in touch with each other. Lot-line structures on abutting property are susceptible to damage during construction, increasing the cost and risk of a project. Where multiple buildings were built at the same, as is usually the case with row houses, buildings may share party walls and foundations that straddle the property line. Lot-line structures and party walls, in particular, can greatly complicate demolition, sometimes requiring an adjacent building to be stabilized or shored. If the adjacent building is old and the new building is to have a basement, underpinning may be required.

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Urban Construction is Different

After decades of decline in the mid-to-late 20th century, the economic vitality and safety of many urban cores have stabilized, making them more attractive for workers and residents. The productivity and increased potential for economic activity that comes from dense development had made households and firms willing to pay a premium for space in city centers and accessible urban neighborhoods. Modern urban renewal now emphasizes “placemaking” in which new development interacts with its environment to create communities with activity throughout the day and night.

The increased interest in living and working in cities has placed a higher demand on the built environment. The return to cities has directly increased demand for residential and office buildings, but has also increased demand for space to accommodate businesses used by urban residents and firms, as well as for the transportation and utility infrastructure necessary for a complex urban eco-system to function.

This demand for buildings and infrastructure is not without challenges. Construction in the urban environment is higher cost and higher risk than building in an undeveloped area, due to logistical constraints and existing facilities on and adjacent to the site. These challenges are compounded when dense urban development requires new facilities to be constructed below ground. Continue reading “Urban Construction is Different”

Missing Scope for Urban Construction Projects

Much of the design and construction community is focused on new construction on greenfield sites. Or, at the very least, they primarily take on projects on isolated or generously sized sites with adequate space for logistics and construction activities and have relatively little potential for direct impact on abutters and the public. Projects like these are often characterized by detached buildings, significant landscape and site work, and large amounts of parking.

However, almost anywhere you go there are urban centers, although many of them are small. Outside a few large cities, architects, engineers and contractors who spend most of their time on non-urban projects and are unfamiliar with the constraints and risks of urban sites may occasionally find themselves working on one.

This can lead to missing pieces in the project scope. When no one is clearly responsible for problems that commonly arise in urban construction, they are likely to be overlooked, increasing the cost and risk of the project. Owners, design professionals and constructors who are not accustomed to protecting party walls, underpinning foundations and performing pre-construction surveys may miss critical opportunities to keep the project cost and schedule on track. Continue reading “Missing Scope for Urban Construction Projects”

Site-Structural LinkedIn Group

Are you on LinkedIn? There is now a LinkedIn group for Site-Structural Engineering that is intended as a forum for discussing problems, solutions and best practices for interfacing new construction to congested sites in the urban environment. If you are new to urban construction, it is a good place to ask questions, tap into the experience of others and get help with your own site-structural issues.

What’s Wrong with Your Monitoring Plan

Construction, particularly in the urban environment, often exposes nearby structures and facilities to hazards, some of which are difficult to predict precisely and manifest as the work progresses. Impacts of this nature are associated with excavations, tunneling and foundation construction methods, and often require monitoring of potentially impacted structures and facilities. A monitoring program may include a variety of means of observation and measurements, including periodic visual and photographic observations of the work and adjacent properties, survey readings and instrumentation to measure displacement, vibrations, groundwater levels and other phenomena.

Commonly used construction monitoring techniques have been available for over 50 years. Technology has reduced the cost and expanded the options for monitoring programs. In spite of this, the full benefit of construction monitoring is often not realized. Here are a few things that can be wrong with the monitoring program for your project:

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Site-Structural Engineering for the Urban Environment

Having projects in the urban environment representing a large proportion of my career experience, I am always a little surprised when I encounter design professionals and contractors who do not fully appreciate the challenges and constraints associated with building on urban sites. While a lot of design professionals, contractors and other stakeholders have urban project horror stories, they do not necessarily associate those adversities with choices that were made or not made during the project. It is almost as if they believe that nothing can be done.

Perhaps I should not be surprised. The fact is that most of the Architecture, Engineering and Construction (A/E/C) industry is focused outside of the urban cores. In a lot of major metropolitan areas, development has focused on low-density sprawl with large parking lots and generous setbacks. For these projects, consideration of the outside world may be limited to curb cuts and utility connections. Is it any wonder then that designers and constructors underestimate what it takes to build on a constrained urban lot. Continue reading “Site-Structural Engineering for the Urban Environment”

If Your New Neighbor is a Construction Site

Occasional inconvenience from construction is a fact of life, especially for those of us who live or work in an urban area. Depending on how close the construction is to your home or business, the potential impacts might be more significant than traffic delays or noise. Construction projects can cause damage to nearby buildings and infrastructure, requiring risk mitigation, protection and performance monitoring.

Most construction damage is caused by vibration, foundation movement or impacts from striking objects, material or equipment. When new construction and adjacent structures are both built up to the property lines, as is typical in many cities, these risks are increased and additional structural and building envelope issues can occur, especially if the adjacent building once shared a party wall with previous buildings on the construction site. Continue reading “If Your New Neighbor is a Construction Site”

Why the Design Team for Urban Projects Should Consider Support of Excavation

A while back, I looked at a small support of excavation project in a major city that illustrated some of the issues that can arise when excavation support and underpinning are not considered during the design process of an urban project, especially a small urban project.The project involved a horizontal addition to an attached single-family dwelling: a very typical project type in cities, and about as simple as new construction can get in the urban environment. However, the existing basement was to be extended below the addition, requiring several feet of excavation on a small site with impacted abutting properties on two sides. Consequently, support of excavation would be required, unless the neighbors would be willing to lose the use of their backyards during construction.

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Engineering Like a Historian

One of the fundamental ways that construction in the urban environment is different from building elsewhere is the potential to damage adjacent structures. This risk becomes significant when adjacent structures are older and abut the lot lines, especially if those structures shared party walls with demolished buildings formerly on the project site. This scenario often requires measures to protect the adjacent structure from foundation movement, moisture infiltration and falling objects, among other hazards. Managing the risk to these adjacent structures requires an understanding of how they were built and how they behave structurally. However, drawings of these building are usually not available, if they ever existed. Further, it is often not feasible to thoroughly investigate these structures due to the cost involved and the fact that adjacent owners typically will not permit invasive explorations. Continue reading “Engineering Like a Historian”