Structural Defects - New Home
Many new houses are designed by architects that are not completely qualified to perform structural design.
Buyers of a new house should consider having their own independent structural evaluation performed by a qualified professional engineer.
Structural evaluation is important for a house with large open spaces or complex geometry. For open areas, detailed structural design is required for long-span beam-elements (girders, joists) and relatively large loads. For complex geometry, careful design is necessary to ensure that all loads are properly distributed through the structure, to foundations.
Structural evaluation is especially important for houses where design wind speed (per building code) is 100 mph or greater.
When purchasing a new home from a builder / developer, buyers should always insist that the builder provide the following documents;
(1) Complete set of certified building design plans. Plans must be certified ("sealed") by the architect (and engineer if applicable). Although difficult to obtain, you should also insist that plans show all "as-built" conditions that are different from, or additional to, details shown on original design plans. Such "as-built" plans should also be certified by the original design professional or another qualified professional (architect or engineer).
(2) If roof trusses or floor trusses were installed, obtain a certified set of truss diagrams, plus placement (layout) plan. If the name and license number of the responsible professional engineer is not clearly listed on truss diagrams, make sure that you obtain this information from the builder or code official. Ask questions to determine whether or not permanent bracing required by the truss designer has been properly designed (by the building designer), installed and inspected.
Having certified building plans (and truss diagrams) is essential to allow for thorough investigation of any defects that may occur after the buyer moves into the house. Having original building plans can also be very useful (and minimize design fees) in the event alterations are made after the house is built.
For roof truss installations, determination of whether required bracing has been properly designed and installed is practically impossible without careful evaluation by a qualified structural engineer.
Design & Construction
For a new development, design plans are typically prepared by an architect working directly for the builder. However, such arrangement, which is effectively "design-build", can lead to lack of proper design since there is an inherent conflict of interest when the builder (instead of the eventual owner) is paying the architect directly. Of course the homeowner pays for the architect indirectly in the purchase price, but the conflict remains.
The vast majority of new home buyers have no idea that there even is an architect responsible for design. They simply "see" the builder.
All-too-often, architects "delegate" essential design functions to the contractor or material suppliers. In many such cases, no design details are prepared by anyone to show key requirements. If the architect fails to follow up, major structural defects can occur.
When necessary structural information is not provided on plans, builders should request additional details from the architect. If the architect does not supply such details, the builder should obtain necessary details from a qualified professional engineer (and consider billing architect for the cost). However many builders tend to barge ahead without first obtaining clarification from any licensed professional. Subcontractors may not even know enough to realize design details are missing. Defective construction can be expected as a result.
Builders tend to get away with such defective construction due to the following factors, which they are generally aware of;
(1) Standard safety factors inherent in the design process. Design loads, which are much greater than ordinary loads, typically have an expected occurrence of once every 50 years. Material failure capacity is typically much greater than allowable design capacity, per building code or manufacturer specifications.
(2) Lack of inspection during construction. Almost universally, the public has the gross misconception that municipal code officials and inspectors are responsible for design and construction, and therefore have "certified" the final product. The fact is that the building designer (usually an architect for residential) has complete responsibility for proper design. Code officials are generally not licensed architect or engineers. The builder has complete responsibility for proper construction, whether municipal inspectors are paying attention or not.
(3) Tendency of home owners to give a very large benefit of doubt to "their" builder. This strange-but-true phenomenon, observed on several projects, has been termed by this writer as the "stuck-home" syndrome (you may appreciate that more having lived through the 1960s / 1970s). Many homeowners take offense when some "outsider" identifies design and construction defects with the house that they purchased new.