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Many details fit together to make up a building. The most complex and critical of architectural details concern the building envelope, which is simply the roof and the facade (called "building skin"). These details are the subject of this article.
Details are vital to the building process. Clear details facilitate bidding the project and buying out the subcontracts. Good details make the lives of everyone participating in the construction process easier, from the shop draftsman to the fabricator and the site superintendent.
Well-thought-out details not only establish a "language" for the building, but they also affect the life and maintainability of the building. Many potential flaws will not show up for 15 years or more, long after the participants are gone. Correcting problems in an occupied building is both costly and difficult.
Details are experienced close up and in a more immediate fashion than the "big picture." Architectural details are noticed by the man in the street. A masterpiece that, after fifteen years, begins to show spalled concrete, rust stains, or panels twisted out of plane does not make a good impression. It does not matter how innovative the building was when initially completed.
Buildings are cultural artifacts. There is a certain delight in the well-made object. Yes, we all take "things" for granted, but well-made things provide a sense of order and stability, harmony, an indication that society cares enough to do something well. A well-made building has a physical reality that transcends ideas.
Construction Sequence
Flexibility in the sequence of construction is possible with good details. Consideration of anchorage, sheet metal, and caulking is critical for flexibility.
The contractor who is awarded a project will set out to erect the building in the most efficient manner that suits his purchasing and scheduling activities. Each subcontract must be bought out separately. The scope of work and the related production and delivery dates in each subcontract affect the construction sequence.
Many parts of the construction sequence are givens; i.e., the foundation must be in place before erection of structural steel. But there are many areas where there can be flexibility. Roofing, for example, can begin before, during, or after the installation of the curtain-wall. Window frames can go in as masonry is erected or after all the masonry openings are in place. And the sequence may change during construction to accommodate an unanticipated problem such as late delivery of window frames. By permitting a flexible construction sequence, well-thought-out details directly affect the efficiency and thus the cost of construction.
To control costs for the owner and allow flexibility for the contractor, several alternative suppliers are usually specified for each manufactured item. Alternative suppliers furnish products that may vary in some way but provide equivalent performance and value to the owner. The architect must be familiar with this range of variation in order to provide details that minimize the impact on adjoining work included in other subcontracts.
Tolerance
There are two aspects of construction tolerance in detailing: manufacturing tolerance and erection tolerances.
Manufacturing tolerances express the acceptable range of deviation from a specified dimension. Manufactured items such as windows and aluminum extrusions are quite precise. Manufactured wood products such as glulam beams are much more precise than framing lumber. Masonry tolerances vary by product type. Site-fabricated items tend to be less precise than off-site manufactured items. Perhaps the most difficult material to control is cast in place concrete.
During construction, the manufactured items must fit into the constructed framework at the job site. This setting must also have certain tolerances for being straight and true, level, plumb, smooth, and square. How well the details account for tolerances affects not only the ease of construction but also the aesthetics and the integrity of the building.
Erection tolerances are the amount of maneuvering room allowed in the framework into which an object must fit. The object must be rigged, slid, twisted, set, shimmed, and finally anchored into place. Wrench and hand clearances must be considered for installation of fasteners.
Since tolerances for materials are specified by the architect, a working knowledge of what is achievable is necessary. The contractor can only furnish what can be "bought" in the marketplace. Furthermore, asking for more quality than is needed today may confuse participants and add needless expense.
Perhaps the most critical aspect of detailing is the dynamic relationship of the various parts of the building assembly. Because buildings sway with the wind and with earthquake forces, the relationship between the exterior cladding and the structural frame must be analyzed carefully. Similarly, materials grow and shrink differently with respect to each other and in hot and cold weather.
Architecture and building differ from other manufacturing activities in that each building is a prototype-a large, expensive prototype. Even with computer molding, testing of building materials and large-curtain walls mock-ups, there are still a great many unknowns. Faith in modern engineering and today's interest in minimizing costs are pushing the edge of allowable risk.
Our understanding of materials is only partly based upon science. The rest is precedent, experience, intuition, and observation. The city is a working building science laboratory of which the detailer must be a keen observer. Some of "those really creative ideas" are just not done, for good reason, although the reasons have perhaps long been forgotten. The detailer could do worse than copy details that are known to work. Within the bounds of existing knowledge there is a wide range of possibilities to create artistic effect without substantial risk.
Each building constructed consumes a great deal of society's resources and is part of our environment for a long time. Careful attention to materials, detailing, and quality of workmanship will provide buildings that are assets to our cities and are easily manageable by our building owners.
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