An estimate is necessary to give the owner an accurate idea of the cost to help him to decide if the work can be undertaken as proposed or needs to be curtailed or abandoned, depending upon the availability of funds and potential direct and indirect benefits. For government works proper sanction has to be obtained for allocating the required amount. Works are often let out on a lump sum basis and in this case the Estimator must be able to know exactly how much expenditure he is going to incur on them.
1. Estimating Materials
From the estimate of a work it is possible to determine what materials and in what quantities will be required for the work so that the arrangements to procure them can be made.
2. Estimating Labor
The number and kind of workers of different categories who will have to be employed to complete the work in the specified time can be found out from the estimate.
3. Estimating Plant
An estimate will help to determine amount and kind of equipment needed to complete the work.
4. Estimating Time
The estimate of a work and the past experience enable one to estimate quite closely the length of time required to complete a work. Whereas the importance of knowing the probable cost needs no emphasis, estimating materials, labor, plant and time is absolutely useful in planning and execution of any work.
The legal restrictions on buildings begin with local zoning ordinances, which govern the types of activities that may take place on a given piece of land, how much of the land may be covered by buildings, how far buildings must be set back from adjacent property lines, how many parking spaces must be provided, how large a total floor area may be constructed, and how tall the buildings may be. In larger cities, zoning ordinances may include fire zones with special fire-protection requirements, neighborhood enterprise districts with economic incentives for new construction or revitalization of existing buildings, or other special conditions.
In addition to its zoning ordinances, local governments regulate building activity by means of building codes. Building codes protect public health and safety by setting minimum standards for construction qualitycations services. structural integrity, durability, livability, accessibility, and especially fire safety.
Most building codes in North America are based on one of several model building codes, standardized codes that local jurisdictions may adopt for their own use as an alternative to writing their own.
In Canada, the National Building Code of Canada is published by the Canadian Commission on Building and Fire Codes. It is the basis for most of that country’s provincial and municipal building codes.
In the United States, the International Building Code® is the predominant model code. This code is published by the International Code Council, a private, nonprofi t organization whose membership consists of local code officials from throughout the country.
It is the basis for most U.S. building codes enacted at the state, county, and municipal levels. The International Building Code (IBC) is the first unifi ed model building code in U.S. history. First published in March 2000, it was a welcome consolidation of a number of previous competing regional model codes.
Building-code-related information in this book is based on the IBC.
The IBC begins by defi ning occupancy groups for buildings as follows:
• Groups A-1 through A-5 are public Assembly occupancies: theaters, auditoriums, lecture halls, nightclubs, restaurants, houses of worship, libraries, museums, sports arenas, and so on.
• Group B is Business occupancies: banks, administrative offi ces, higher- education facilities, post offices, banks, professional offices, and the like.
• Group E is Educational occupancies: schools for grades K through 12 and day-care facilities.
• Groups F-1 and F-2 comprise industrial processes using moderatefl ammability or noncombustible materials, respectively.
• Groups H-1 through H-5 include various types of High Hazard occupancies in which toxic, corrosive, highly flammable, or explosive materials are present.
• Groups I-1 through I-4 are Institutional occupancies in which occupants under the care of others may not be able to save themselves during a fire or other building emergency, such as health care facilities, custodial care facilities, and prisons.
• Group M is Mercantile occupancies: stores, markets, service stations, and salesrooms.
• Groups R-1 through R-4 are Residential occupancies, including apartment buildings, dormitories, fraternity and sorority houses, hotels, one- and two-family dwellings, and assisted living facilities.
• Groups S-1 and S-2 include buildings for Storage of moderate- and low-hazard materials, respectively.
• Group U is Utility buildings. It comprises agricultural buildings, carports, greenhouses, sheds, stables, fences, tanks, towers, and other secondary buildings.
The IBC’s purpose in establishing occupancy groups is to distinguish various degrees of need for safety in
buildings. A hospital, in which many patients are bedridden and cannot escape a fire without assistance from others, must be built to a higher standard of safety than a hotel or motel.
A warehouse storing noncombustible masonry materials, which is likely to be occupied by only a few people, all of them able-bodied, can be constructed to a lower standard than a large retail mall building, which will house large quantities of combustible materials and will be occupied by many users varying in age and physical capability. An elementary school requires more protection for its occupants than a university building.
A theater needs special egress provisions to allow its many patrons to escape quickly, without stampeding, in an emergency.
These definitions of occupancy groups are followed by a set of definitions of construction types. At the head of this list is Type I construction, made with highly fire-resistant, noncombustible materials. At the foot of it is Type V construction, which is built from combustible wood framing—the least fire-resistant of all construction types. In between are Types II, III, and IV, with levels of resistance to fire falling between these two extremes.
With occupancy groups and construction types defi ned, the IBC proceeds to match the two, stating which occupancy groups may be housed in which types of construction, and under what limitations of building height and area.
This table gives values for the maximum building height, in both feet and number of stories above grade, and the maximum area per floor for every possible combination of occupancy group and construction type. Once these base values are adjusted according to other provisions of the code, the maximum permitted size for a building of any particular use and type of construction can be determined.
This table concentrates a great deal of important information into a very small space. A designer may refer to it with a particular building type in mind and find out what types of construction will be permitted and what shape the building may take. Consider, for example, an office building. Under the IBC, a building of this type belongs to Occupancy
Group B, Business. Reading across the table from left to right, we find immediately that this building may be built to any desired size, without limit, using Type I-A construction.
Choosing Building Systems
A building begins as an idea in someone’s mind, a desire for new and ample accommodations for a family, many families, an organization, or an enterprise. For any but the smallest buildings, the next step for the owner of the prospective building is to engage, either directly or through a hired construction manager, the services of building design professionals.
An architect helps to organize the owner’s ideas about the new building, develops the form of the building, and assembles a group of engineering specialists to help work out concepts and details of foundations, structural support, and mechanical, electrical, and community
This team of designers, working with the owner, then develops the scheme for the building in progressively finer degrees of detail. Drawings and written specifications are produced by the architect–engineer team to document how the building is to be made and of what. The drawings and specifications are submitted to the local government building authorities, where they are checked for conformance with zoning ordinances and building codes before a permit is issued to build. A general contractor is selected, either by negotiation or by competitive bidding, who then hires subcontractors to carry out many specialized portions of the work. Once construction begins, the general contractor oversees the construction process while the building inspector, architect, and engineering consultants observe the work at frequent intervals to be sure that it is carried out according to plan. Finally, construction is finished, the building is made ready for occupancy, and that original idea, often initiated years earlier, is realized.
Although a building begins as an abstraction, it is built in a world of material realities. The designers of a building—the architects and engineers— work constantly from a knowledge of what is possible and what is not. They are able, on the one hand, to employ a seemingly limitless palette of building materials and any of a number of structural systems to produce a building of almost any desired form and texture. On the other hand, they are inescapably bound by certain physical limitations: how much land there is with which to work; how heavy a building the soil can support; how long a structural span is feasible; what sorts of materials will perform well in the given environment. They are also constrained by a construction budget and by a complex web of legal restrictions.
Those who work in the building professions need a broad understanding of many things, including people and culture, the environment, the physical principles by which buildings work, the technologies available for utilization in buildings, the legal restrictions on building design and use, the economics of building, and the contractual and practical arrangements under which buildings are constructed. This book is concerned primarily with the technologies of construction—what the materials are, how they are produced, what their properties are, and how they are crafted into buildings. These must be studied, however, with reference to many other factors that bear on the design of buildings, some of which require explanation here.
In addition, a sidebar in nearly every chapter describes the major issues of sustainability related to the materials and methods discussed in that chapter. These will be helpful in weighing the environmental costs of one material against those of another, and in learning how to build in such a way that we preserve for future generations the ability to meet their building needs in a reasonable and economical manner.
For more information on organizations whose mission is to raise our awareness and provide the knowledge that we need to build sustainably, see the references listed at the end of this chapter.
In the United States, the most widely adopted method for rating the environmental sustainability of a building’s design and construction is the U.S. Green Building Council’s Leadership in Energy and Environmental Design, or LEED™, rating system.
LEED for New Construction and Major Renovation projects, termed LEED-NC, groups sustainability goals into categories including site selection and development, efficiency in water use, reductions in energy consumption and in the production of atmospheric ozone-depleting gases, minimizing construction waste and the depletion of nonrenewable resources, improving the quality of the indoor environment, and encouraging innovation in sustainable design and construction practices (Figure 1.1).
Within each category are specifi c credits that contribute points toward a building’s overall assessment of sustainability.
Depending on the total number of points accumulated, four levels of sustainable design are recognized, including, in order of increasing performance, Certified, Silver, Gold, and Platinum.
The process of achieving LEED certification for a proposed new building begins at the earliest stages of project conception, continues throughout the design and construction of the project, and involves the combined efforts of the owner, designer, and builder.
During this process, the successful achievement of individual credits is documented and submitted to the
Green Building Council, which then makes the final certification of the project’s LEED compliance.
The U.S. Green Building Council continues to refi ne and improve upon LEED-NC and is expanding its family of rating systems to include existing buildings (LEED-EB), commercial interiors (LEED-CI), building core and shell construction (LEED-CS), homes (LEED-H), and other categories of construction and development. Through international sister organizations, LEED is being implemented in Canada and other countries. Other green building programs, such as the Green Building Initiative’s Green Globes, the National
Association of Home Builders’ Green Home Building Guidelines, and the International Code Council and National Association of Home Builders’ jointly developed National Green Building Standard, offer alternative assessment schemes.
Some green building efforts focus more narrowly on reducing building energy consumption, a measure of building performance that frequently correlates closely with the generation of greenhouse gas emissions and global warming trends. The American Society of Heating, Refrigerating and Air-Conditioning Engineers’ Advanced Energy Design Guides and the U.S. Environmental
Protection Agency’s Energy
Star program both set goals for reductions in energy consumption in new buildings that exceed current
national standards. These standards can be applied either as stand-alone programs or as part of a more comprehensive effort to achieve certification through LEED or some other green building assessment program.
Buildings can also be designed with the goal of zero energy use or carbon neutrality. A net zero energy
building is one that consumes no more energy than it produces, usually when measured on an annual basis to account for seasonal differences in building energy consumption and on-site energy production. Net zero energy use can be achieved using current technology combining on-site renewable energy generation (such as wind or solar power), passive heating and cooling strategies, a thermally efficient building enclosure, and highly efficient mechanical systems and appliances.
A carbon-neutral building is one that causes no net increase in the emission of carbon dioxide, the most prevalent atmospheric greenhouse gas. If emissions due only to building operation are considered, the calculation is similar to that for a net zero energy building. If, however, the embodied carbon in the building’s full life cycle—from materials extraction and manufacturing, through building construction and operations, to demolition, disposal, and recycling—is considered, the calculation becomes more complex. Carbon-neutral calculations may also consider the site on which the building resides. For example, what is the carbon footprint of a fully developed building site, including both its buildings and unbuilt areas, in comparison to that of the site prior to construction or in comparison to its natural state prior to human development of any kind? Another possible consideration is, what role, if any, should carbon offsetting (funding of offsite activities that reduce global carbon emissions, such as planting of trees), play in such calculations? Questions such as these and the concepts of sustainability and how they relate to building construction will continue to evolve for the foreseeable future.
What planning and design strategies can be used to extend the useful life of buildings, thereby forestalling resource intensive demolition and construction of new buildings? When demolition is inevitable, how will the building be demolished and disposed of, and will any part of this process cause pollution of air, water, or soil? Can demolished materials be recycled into new construction or diverted for other uses rather than disposed of as wastes?
One model for sustainable design is nature itself.
Nature works in cyclical processes that are self-sustaining and waste nothing. More and more building professionals are learning to create buildings that work more
nearly as nature does, helping to leave to our descendants a stock of healthful buildings, a sustainable supply of natural resources, and a clean environment that will enable them to live comfortably and responsibly and to pass these riches on to their descendants in a never-ending succession.
How much energy is expended in transporting a material from its origins to the building site, and what pollutants are generated? How much energy and water are consumed on the building site to put the material in place? What pollutants are associated with the installation of this material in the building? What wastes are generated, and how much of them can be recycled?
Sustainability must be addressed on a life-cycle basis, from the origins of the materials for a building, through the manufacture and installation of these materials and their useful lifetime in the building, to their eventual disposal when the building’s life is ended. Each step in this so-called cradle-to-grave cycle raises questions of sustainability.
Origin and Manufacture of Materials for a Building Are the raw materials for a building plentiful or rare? Are they renewable or non renewable? How much of the content of a material is recycled from other uses? How much embodied energy is expended in obtaining and manufacturing the material, and how much water? What pollutants are discharged into air, water, and soil as a result of these acts? What wastes are created? Can these wastes be converted to useful products?
In constructing and occupying buildings, we expend vast quantities of the earth’s resources and generate a significant portion of the earth’s environmental pollution: The U.S. Green Building Council reported in 2008 that buildings account for 30 to 40 percent of the world’s energy use and associated greenhouse gas emissions. Construction and operation of buildings in the United States accounted for more than one-third of this country’s total energy use and the consumption of more than twothirds of its electricity, 30 percent of its raw materials, a quarter of its harvested wood, and 12 percent of its fresh water. Building construction and operation is responsible for nearly half of this country’s total greenhouse gas emissions and close to a third of its solid waste stream. Buildings are also significant emitters of particulates and other air pollutants. In short, building construction and operation cause many forms of environmental degradation that place an increasing burden on the earth’s resources and jeopardize the future of the building industry and societal health and welfare.
Sustainability may be defined as meeting the needs of the present generation without compromising the ability of future generations to meet their needs.
By consuming irreplaceable fossil fuels and other nonrenewable resources, by building in sprawling urban patterns that cover extensive areas of prime agricultural land, by using destructive forestry practices that degrade natural ecosystems, by allowing topsoil to be eroded by wind and water, and by generating substances that pollute water, soil, and air, we have been building in a manner that will make it increasingly difficult for our children and grandchildren to meet their needs for communities, buildings, and healthy lives.
On the other hand, if we reduce building energy usage and utilize sunlight and wind as energy sources for our buildings, we reduce depletion of fossil fuels. If we reuse existing buildings imaginatively and arrange our new buildings in compact patterns on land of marginal value, we minimize the waste of valuable, productive land. If we harvest wood from forests that are managed in such a way that they can supply wood at a sustained level for the foreseeable future, we maintain wood construction as a viable option for centuries to come and protect the ecosystems that these forests support. If we protect soil and water through sound design and construction practices, we retain these resources for our successors. If we systematically reduce the various forms of pollution emitted in the processes of constructing and operating buildings, we keep the future environment cleaner. And as the industry becomes more experienced and committed to designing and building sustainably, it becomes increasingly possible to do these things with little or no increase in construction cost while creating buildings that are less expensive to operate and more healthful for their occupants for decades to come.
Realization of these goals is dependent on our awareness of the environmental problems created by building activities, knowledge of how to overcome these problems, and skill in designing and constructing buildings that harness this knowledge.
While the practice of sustainable design and construction, also called green building, remains a relatively recent development in the design and construction industry, its acceptance and support continue to broaden among public agencies, private developers, building operators and users, architectural and engineering firms, contractors, and materials producers.
With each passing year, green building techniques are becoming less a design specialty and more a part of mainstream practice.
Different building systems: different structural systems, different systems of enclosure, and different systems of interior ﬁnish.
Each system has characteristics that distinguish it from the alternatives.
Sometimes a system is distinguished by its visual qualities, as one might acknowledge in choosing one type of granite over another, one color of paint over another, or one tile pattern over another.
However, visual distinctions can extend beyond surface qualities; a designer may prefer the massive appearance of a masonry bearing wall building to the slender look of an exposed steel frame on one project, yet would choose the steel for another building whose situation is different.
Again, one may choose for purely functional reasons, as in selecting terrazzo ﬂooring that is highly durable and resistant to water instead of more vulnerable carpet or wood in a restaurant kitchen.
One could choose on purely technical grounds, as, for example, in electing to posttension a long concrete beam for greater stiffness rather than rely on conventional steel reinforcing. A designer is often forced into a particular choice by some of the legal constraints identiﬁed later in this chapter.
A choice is often inﬂuenced by considerations of environmental sustainability.
And frequently the selection is made on purely economic grounds.
The economic criterion can mean any of several things: Sometimes one system is chosen over another because its ﬁrst cost is less; sometimes the entire life-cycle costs of competing systems are compared by means of formulas that include ﬁrst cost, maintenance cost, energy consumption cost, the useful lifetime and replacement cost of the system, and interest rates on invested money; and, ﬁnally, a system may be chosen because there is keen competition among local suppliers and/or installers that keeps the cost of that system at the lowest possible level.
This is often a reason to specify a very standard type of rooﬁng material, for example, that can be furnished and installed by any of a number of companies, instead of a newer system that is theoretically better from a functional standpoint but can only be furnished by a single company that has the special equipment and skills required to install it.
One cannot gain all the knowledge needed to make such decisions from a textbook.
It is incumbent upon the reader to go far beyond what can be presented here—to other books, to catalogs, to trade publications, to professional periodicals, and especially to the design ofﬁce, the workshop, and the building site.
Thereis no other way to gain much of the required information and experience than to get involved in the art and business of building. One must learn how materials feel in the hand; how they look in a building; how they are manufactured, worked, and put in place; how they perform in service; how they deteriorate with time. One must become familiar with the people and organizations that produce buildings—the architects, engineers, materials suppliers, contractors, subcontractors, workers, inspectors, managers, and building owners—and learn to understand their respective methods, problems, and points of view.
In the meantime, this long and hopefully enjoyable process of education in the materials and methods of building construction can begin with the information presented in this textbook.