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Prescriptive Residential Construction Vs New Design Standards[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "SEA International List" <seaint(--nospam--at)seaint.org>
- Subject: Prescriptive Residential Construction Vs New Design Standards
- From: "Dennis S. Wish PE" <wish(--nospam--at)cwia.com>
- Date: Fri, 2 Oct 1998 13:05:42 -0700
Bob Bossi (Past Chair, Conventional Construction Task Force) wrote:
"It is true that conventionally framed buildings won't "calculate". So what. It is how they perform that counts. Conventional construction has a long history of satisfactory performance in earthquakes. Yes, there have been failures of older buildings with unbraced cripple walls but we have retrofit standards to correct this. There is no loophole in the code. Conventional construction was included in the code by the same methods as any other provision. Developers are not unethical to use it. I have never seen any developer market a new residence based on its seismic resistance. The purpose of the building code is the protection of the health and safety of the general public, not the protection of individuals from property damage or economic loss"
"The definition of conventional framing has not increased. As of the 1994 UBC, the undefined terms "unusual size and shape" have been replaced by detailed limits on occupancy, dead load, room size (braced line spacing) and degree of irregularity. Additional connection have been required. As a result, far fewer building will be able to qualify for the use of conventional construction."
"Structural Observation should not be necessary for conventionally framed buildings. An AB 717 qualified (ICBO certified) local building inspector should be able to make all necessary inspections. "
"The California Contractor's State License Board is also in the process of developing a "merit badge" system. "
"Where are "we" creating more regulations that discourage quality control?"
"It is unlikely because the more restrictive conventional construction provisions will not allow this to happen. Ther is however the partially ebgineered, partially conventional structures. This, howver, is not something the building code can fix as it would require, in California at least, a change to both the engineer's and architect's acts.
With this said, I still believe that there is room for improvement in the conventional construction provisisions of the UBC, IBC and NEHRP but I also belong to the Frank, "where are the bodies", Lew school. Take a look at all the conventionally framed buildings that have ever perfrormed so poorly as to cause death or serious injury to their occupants and ask yourself would this of occured had they been constructed to conform to the current codes conventional construction provisions. To the extent that the answer is no, the cuurrent provisions are adequate. If you identify any areas where the answer is yes, then that is where the code need to be changed. Anything else is regulation for regulation sake.
Remember, we can always add to the code to make construction more expensive but only at significant social costs. "
Bob, here are some of the driving concerns.
1. The Insurance Industry reports close to $60 Billion dollars in damage to residential homes from the Northridge earthquake - Figures are high from Hurricanes such as Andrew. The insurance industry has once again pulled out of California (for earthquake coverage) relying upon a new state plan with an increased deductable from 10% to 15% or more.
2. I believe there is a growing concern that the code must provide for more than life safety - to help reduce the historic level of costly damage resulting from a combination of design inadequacies, and construction quality failures. I believe that other organizations believe this to be true - National Association of Home Builders Research Center seems very concerned with this issue - and I applaud them for finding the financial bodies.
3. I have been pretty clear about my concerns with the marketing of a residential homes. It should be easy for you to prove that the majority of homebuyers believe that all homes are protected by code and are designed by the same methodology. You and I know that is not the case - and so does the developer. Mind you, devlopers of large tracts like Kauffman and Broad can't get away with this - but the small developer of five to ten homes a year can and does. He is smart enough to know exactly where his money is spent in the construction of a residential home and knows full well that he is protected from liablity as long as he complies with conventions framing provisions.
I believe it is unethical to sell two products and depict them to be of the same quality when the fact is that one will not come up to the numeric standards of the other (and thus will not perform the same). In this case, I believe the public needs protection by disclosure. they should be aware of the homes expected performance standard so as to make an intellegent choice based upon disclosure of the facts.
4. There are quite a few ommissions in the prescriptive method that can lead to problems in the field.
Tell me where, in this section of the code, it lead the non-professional to a prescriptive beam or header design? It does mention that headers need to be designed but does not stipulate how or by whom. Therefore, the building official historically accepts the contractor or builders plans which arbitrarily pick header and beam sizes.
What happens when a prescriptive set of plans is submitted for permit issuance and the building department technician is neither an engineer of architect? As long as his interpretation matchs the contractors (who must have historically been doing it right to get so many permits in our town) who finds the mistakes?
You suggest that "The California Contractor's State License Board is also in the process of developing a "merit badge" system. " I would applaud this but when will it cover these issues. When will the CCSLB require a framer to be required to have an understanding of this section of the code. Today, anyone who can lift a hammer can call themselves a "Framer" - very few whom I've met have ever looked at the UBC.
Where in the discussion of interior braced walls does it explain that the top of the interior resisting wall must be connected to the roof diaphragm? I don't see a reference to top of wall connection in 2320.11.3 or 2320.11.4 of the '97 code (or anywere else in section 2320.11) and don't remember seeing it in either the '91 or '94 UBC.
Is the framer or designer expected to sign the plans to verify that he or she has designed in compliance with conventional framing and understands both the rhetoric and intention of this code section? Or, is compliance to conventional framing standards the responsiblity of the building official to detect?
My last comment is to your statement "Remember, we can always add to the code to make construction more expensive but only at significant social costs. ".
I agree with you here and this is why I have such a problem with Conventional framing provisions. Unless you write a code that can be followed without the need of "designed" elements, you invite misinterpretation and errors in construction. The code is written for professionals, not laypersons. The extent of damage from Northridge Earthtquake created stricter codes (which conventional framing remains exempt). Therefore, the code is used to maken construction more costly and the expense of a discontinuity within the building industry.
Dennis Wish PE
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