Seismic Codes: "Much Ado About Nothing"

[Riversong]

In the 2000 edition of HUD's 434-page Residential Structural Design Guide, I just came across this information:

The 1994 Northridge Earthquake near Los Angeles CA measured 6.4 on the Richter scale (a moderately strong tremor), but produced some of the worst ground motions in recorded history for the US.

Construction Characteristics of Sampled Single-Family Detached Dwellings in Northridge Earthquake

Component Frequency of Construction Characteristics
Number of stories - 79% one - 18% two - 3% other
Wall sheathing - 80% none - 7% plywood - 13% unknown
Foundation type - 68% crawl space - 34% slab - 8% other
Exterior finish - 50% stucco/mix - 45% stucco only - 6% other
Interior finish - 60% plaster board - 26% gypsum board - 14% other/unknown

Damage to Sampled Single-Family Detached Homes in the Northridge Earthquake (percent of sampled homes)

Estimated Damage - None -Low - Moderate - High
Foundation - 90.2% - 8.0% - 0.9% - 0.9%
Walls - 98.1% - 1.9% - 0.0% - 0.0%
Roof - 99.4% -0.6% - 0.0% - 0.0%
Exterior finish - 50.7% - 46.1% - 2.9% - 0.3%
Interior finish - 49.8% -46.0% -4.2% - 0.0%

About 90 percent of the homes in the sample were built before the 1971 San Fernando Valley Earthquake, at which time simple prescriptive requirements were normal for single-family detached home construction. About 60 percent of the homes were built during the 1950s and 1960s, with the rest constructed between the 1920s and early 1990s. Styles ranged from complex custom homes to simple affordable homes. All homes in the sample had wood exterior wall framing, and most did not use structural sheathing for wall bracing. Instead, wood let-in braces, Portland cement stucco, and interior wall finishes of plaster or gypsum wall board provided lateral racking resistance. Most of the crawl space foundations used full-height concrete or masonry stem walls, not wood cripple walls that are known to be prone to damage when not properly braced.

Serious structural damage to foundations, wall framing, and roof framing was limited to a small proportion of the surveyed homes. In general, the homes suffered minimal damage to the elements that are critical to occupant safety. Of the structural elements, damage was most common in foundation systems. The small percent of surveyed homes (about 2 percent) that experienced moderate to high foundation damage were located in areas that endured localized ground effects (i.e. fissuring or liquefaction) or problems associated with steep hillside sites.

The amount of wall bracing using conventional stucco and let-in braces typically ranged from 30 to 60 percent of the wall length (based on the street-facing walls of the sampled one-story homes). However, there was no observable or statistically significant trend between amount of damage and amount of stucco wall bracing. Since current seismic design theory implies that more bracing is better, the Northridge findings are fundamentally challenging yet offer little in the way of a better design theory. At best, the result may be explained by the fact that numerous factors govern the performance of a particular building in a major seismic event. For example, conventional seismic design, while intending to do so, may not effectively consider the optimization of flexibility, ductility, dampening, and strength – all of which are seemingly important.

[emphasis is mine]

[Dick Seibert]

All homes in the sample had wood exterior wall framing, and most did not use structural sheathing for wall bracing. Instead, wood let-in braces, Portland cement stucco, and interior wall finishes of plaster or gypsum wall board provided lateral racking resistance.

I agree, we have way overreacted to earthquakes, most of this has just led to increased costs without other unintended consequences, the only usually engineered requirement that has led to unintended consequences is the use of structural sheathing for wall bracing, this has created a sealing of the wall cavities leading to dryrot and termite infestation within the walls. Installing the usual lath behind stucco has created enormous problems, for instance here is a wall cavity in a 1959 home with the line-wire application used at that time, later replaced by the faster-to-apply paperback lath, walls typically leaked water when the line-wire or paperback lath became overwhelmed, typically 20 minutes, this soaked the sheathing. You can imagine what would have happened were there to have been plywood, or worse, OSB behind that lath. BTW, homes of that era had no insulation to soak up water, water leaks in and drys out with no damage, and I've seen no earthquake damage other than some shifting on foundations due to inadequate bolting, there were many cases of CMU foundations failing from earthquakes, but most of those failures came from soils pressures prior to the earthquake occurrence, we didn't see many of those becasue they were only a few allowed in the 60s before they were banned.

The combination of increased structural codes along with the new energy codes has wreaked all kinds of damage. California has the strictest structural and energy codes in the nation, and has suffered the most with the problems they have created. Much of the scare tactics used come from the so-called "soft-front" buildings built on fill, buildings built on soils subject to liquification need specialized foundations, and soft-front buildings like pictured above need steel frames, but that doesn't mean all buildings need the degree of structural integrity that specialized cases require. Many Victorians with no sheathing of any kind performed quite well through many earthquakes, just redwood siding nailed directly to studs, or stucco homes with with just line-wire or paperback lath and no sheathing like the wall cavity pictured above.

Why California seems on a mission from God to impose it's standards on the rest of the world is beyond me, but the whole purpose of the ICBO morphing itself into the ICC was to impose these standards on the world, the ICC is still a California corporation but has moved it's headquarters into a green building in Washington DC to capitalize on the green building movement.

BTW, I am a big fan of using systems like Hardy Frames, Simpson Strong-Frame, or Simpson Steel Strong-Wall to eliminate the need of structural sheathing, I am not a fan of Simpson Wood Strong-Wall because they are made from OSB.

[Riversong]

I agree, we have way overreacted to earthquakes

That's interesting coming from you. Didn't you condemn Vermont for not keeping up with California's "high" standards?

California has the strictest structural and energy codes in the nation...Why California seems on a mission from God to impose it's standards on the rest of the world is beyond me

I could have sworn you had bragged about California being the leader in such wonderful developments.

but the whole purpose of the ICBO morphing itself into the ICC was to impose these standards on the world

No, the purpose of the IBC/IRC was to consolidate the three regional codes (UBC, SBC, NBC) into one uniform code.

According to HUD (in 2000):

"The NBC tends to address conditions indigenous to the northeastern quarter of the United States (e.g. frost) while the SBC focuses on conditions in the southeastern quarter of the United States (e.g. hurricanes) and the UBC on conditions in the western half of the United States (e.g. earthquakes)."

"To help resolve the problem of disunity among the three major building codes, the model building code organizations have recently entered into a joint effort (under the auspices of the International Code Council or ICC) to develop a single comprehensive building code called the International Building Code (IBC)."

"To provide a comprehensive, easier-to-use code for residential construction, the three major code organizations participated in developing the International One- and Two-Family Dwelling Code (ICC, 1998), first published in 1971 as the One- and Two-Family Dwelling Code (OTFDC) by the Council of American Building Officials (CABO)."

"The major code organizations are also developing a replacement for the OTFDC in conjunction with the proposed IBC. Tentatively called the International Residential Code for One- and Two-Family Dwellings (IRC), it draws on earlier editions of the OTFDC..."

[Riversong]

Here's another interesting tidbit on the mortality risk of various events: Americans have about a 1 in ten million chance of dying from an earthquake.

[Bill Robinson]

Interesting bit of information.

However it only tells a part of the story.
What is your point?

I was involved in a lot of the remediation as a result that event.
While there may be some overkill in the solutions it is evident the strengthening has saved lives and reduced property damage.
There has been little damage and few deaths from earthquakes in the same area since the mitigation preformed as a result of the Northridge earthquake.
Earthquake Bill

[Dick Seibert]

Riversong:

No I am not bragging about how stiff our codes have become, I'm telling people that where we are is where you are going. What you are reciting is the well-known rationalization for what occurred, but looking at it you can see that the ICC is still a California Corporation that has taken over the process. They made many concessions along the way to bring all to the fold, they claim it was done to prevent the Federales from writing a national code, it was really driven by the NFPA's attempt to hijack the whole process, the NFPA sued the ICBO, wrote it's own building code, the NFPA 5000, and actually "influenced" the California Building Standards Commission into adopting it, then the Democratic governor was recalled over other matters, and one of the first things that the new Republican governor did was "accept the resignations" of the entire commission and appointed a new commission that promptly rescinded the actions of the prior commission and proceeded to adopt the IBC. The main concession to the other code writing bodies was the creation of a simplified residential code, the long fought-for dream of the NAHB, California then refused to adopt it, preferring to adopt the IBC amending it to apply to residential construction at a higher level.

Somehow in the settlement of the NFPA/ICBO litigation the new ICC became dominated by the fire service people, even electing the president, Adolph Zubia, from the ranks of the fire service, Zubia has no certifications in anything but the Fire Inspector II certification, a prerequisite to taking the Fire Inspector II exam is passing the Fire Inspector I exam, it turns out that he passed no examinations.

In the September Minneapolis code hearings there were proposals for more energy efficiency measures, the convention center was swarmed with and dominated by fire service people, the energy proposals and many structural proposals didn't pass (even those to fireproof I Joists and roof trusses for the protection of firefighters), the residential sprinklers did pass. There is all kinds of evidence of the illegal payment of expenses to get fire people there to overwhelm the voting process, these firemen know nothing about building codes, but were there to vote for one thing - fire sprinklers, the FBI and some states are investigating, but upon appeal the ICC, while agreeing to look into it's voting processes, refused to overturn the sprinkler mandate.

At the present time the system is broken and laden with fraud, there are rumors that the ICC is heavily in debt from their move to the very expensive green building in Washington (I've heard triple the normal rent), and with the economy books aren't being sold, and many states are not adopting the 2009 codes becasue of the sprinkler mandate, the ICC makes it's money selling books and training courses for certifications. At the present time there is a two-way fight going on between the greens and the fire people for domination, the structural people seem to have fallen into obscurity at the present time because the greens and the fire people are getting huge amounts of money from the respective manufacturers of products they want mandated.

[Dick Seibert]

Riversong:

You data is old 1987 data, the 3,800 fire deaths per year is now down to under 2,000. Note that deaths from cold and/or heat don't even make the chart, so why the push for energy efficiency if we're going to base codes on safety? The building inspector community is almost 100% against the energy codes, one of their main reasons is that they have nothing to do with their mandate, life and safety, so the question arises: "Have the codes gone too far embracing anything but life and safety?" In the old days the code was designed to "Protect life and safety while increasing the tax base", now I see they've removed the tax base from the published rational.

[NW Architect]

I'd sure like to know the benchmarks used for the none-low-medium-high classifications, and what the sampling of home was. I probably inspected 300SFRs after Northridge and ALL of the samples I looked at had at least moderate structural damage and modetate to severe damage to interior and exterior finishes.

Granted, I and other professionals were ot call in to look at the houses that had lesser damage, and could be successfully assessed by adjusters, so maybe my view is a bit skewed. That said, damn near every structure in the San Fernando Valley had to have repairs done to them.

The pre-Northridge codes served the purpose for which they were intended - to prevent loss of life. Deaths occurred almost exclusively in structures that did not meet the codes.

After Northridge it was decided that the code's purpose needed to be "upped" to add mitigation of cosmetic and structural damages.

The Structural Engineers Council of southern California (if I remember the name right) was the body that did the studies and came up with the recommendations.

None of it has to do directly with ICBO, ICC, or plans for world domination.

[Dick Seibert]

The Structural Engineers Council of southern California (if I remember the name right) was the body that did the studies and came up with the recommendations.

None of it has to do directly with ICBO, ICC, or plans for world domination.

How did it get into the codes then?

The inspectors who frequent their forum all agree that earthquake protection is within the code mandate, where they disagree is whether the energy codes are within the life safety mandate. I think the most extreme comment so far is this from a Rhode Island building official:

OK who wants to Light This Fire
A Practicing Architect for 25 plus years
graduated college in the 70's gas crisis
Built own home without a furnace in New England 20 years ago
Now in State Code Enforcement - "Best Job Ever"

LEED (I whish I'd Thought of it) is a SCAM
They pat you on the back for doing the right thing in the most convoluted way. THEN PICK YOUR POCKET.

LEED is NOT A CODE>>>> it is a group of ner do wells who could not succeed in eiter construction or design who go around the industry like a cat in the house waiting to leave thier Mark!!

I don't agree with him by the way, there has been some progress there are points being considered for plastic free construction and sustainability is finally being emphasized over energy efficiency; however, two days ago I went to their Ask an Expert website and submitted a question, the E-mail was returned as undeliverable, so I found their E-mail address and informed them of the fact that it wasn't working and again posed the question, I haven't heard back, but here were the questions I posed:

I posted the following questions in your ask the experts site and the mail was returned.


1) I've heard that the USGBC is reconsidering the allowance of PVC in the LEED program. With the growing island comprised of 80% plastic, twice the size of Texas in the Pacific, are LEED credits going to be awarded for a plastic-free home? Where does the USGBC stand at this point on the use of all plastics? I am very concerned about the carcinogenic problems posed by PVC.

2) As a California State License Board Industry Expert and Arbitrator I've found many homes suffering from dryrot problems within a few years when plastic wraps (Tyvek, Typar, etc.) are used as opposed to asphalt felts or Grade D Kraft paper, when energy efficiency conflicts with sustainability, where does the USGBS stand?

[Riversong]

I'd sure like to know the benchmarks used for the none-low-medium-high classifications, and what the sampling of home was.

As you suggest, your "sampling" was biased.

The study I refered to was done in 1994 by HUD on homes of no more than two stories. Another HUD study was performed on multi-story residential buildings. The first study (http://www.huduser.org/Publications/PDF/earthqk.pdf) details its assesment methodology in Table 2 on page 18.

"Two groups of building types were surveyed: single-family detached (SFD) properties, and single-family attached and multifamily low-rise (MFLR/SFA) of two stories and under. The SFD survey was conducted as a random single-stage cluster sample. The home at the selected address was surveyed along with two homes on either side, or a total of five homes per site. For the MFLR/SFA survey, the selected building was considered a single structure and all accessible areas or dwelling units within the structure were assessed.

Construction characteristics and damage to 341 SFD homes and 30 MFLR/SFA buildings were recorded. In addition to the statistically-based survey, case studies of damage were performed on 54 SFD and 43 MFLR/SFA buildings. A damage assessment form was completed for each surveyed building."

[NW Architect]

Thanks for the link. I'm satisfied with their definitions and with the geographic area sampled.

It was still a s***pot of economic loss and I'm convinced the codes warranted revision. Whether they got it all right or not remains to be seen.

[Bill Robinson]

As Dick pointed out, the initial intent of the code was life safety.
The code now requires insulation in walls, floors, and roof/ceilings.
How many lives have been saved as a result of that?
And how much additional cost from building damage by limiting the drainage and drying capacity of the wall cavity?

Rather than blame building failure on sheathing, isn't it really filling the wall cavities with insulation the problem?

People did die in the Northridge earthquake, some from inadequately braced buildings. It is reasonable to take action to reduce that loss by strengthening the buildings.
There was also substantial property loss. Subsequent risk of loss has been reduced by strengthening the load path.
It has been noted that many of the failures resulted in homes built with larger window openings. It had less to do with the year built and the wall finishes than how many windows and how little wall. Older homes tended to have fewer windows. They fared better.
Earthquake Bill

[Riversong]

As Dick pointed out, the initial intent of the code was life safety. The code now requires insulation in walls, floors, and roof/ceilings. How many lives have been saved as a result of that?

The purpose of modern municipal building codes is public health, life safety, and general welfare. Minimum room sizes, for instance, have nothing to do with health or life safety.

The scope of "general welfare" has expanded as we've become more cognizant as a society of the impacts of our energy consumption on both local (pollution) and global (climate change, resource depletion) environments.

That some in the building trades refuse to accept the science behind such decisions doesn't make them any less valid or appropriate.

And how much additional cost from building damage by limiting the drainage and drying capacity of the wall cavity? Rather than blame building failure on sheathing, isn't it really filling the wall cavities with insulation the problem?

Building code requirements, particularly in regard to single-family residential homes, should balance social goods against private cost - in other words, be reasonable without being excessive.

But to blame building failures on codes rather than design and construction is to shift the blame from where it belongs - a form of scapegoating for those who refuse to accept their own responsibility. And to blame either sheathing or insulation as THE cause of building deterioration is to misunderstand the synergistic whole-systems nature of a modern house: it's how the elements work together that determines the durability of a system - and the quality of construction.

People did die in the Northridge earthquake, some from inadequately braced buildings. It is reasonable to take action to reduce that loss by strengthening the buildings.

Correct me if I'm wrong, but it appears that death in single-family homes was a non-issue, as there was very little damage and most of that was cosmetic. It seems the death and property damage occured in commercial buildings built on "soft-front" foundations such as parking garages.

Stiffening the codes for commercial buildings makes perfect sense. But there seems to be little justification for strict requirements for single-family homes.

[NW Architect]

. But there seems to be little justification for strict requirements for single-family homes.

I disagree. They may (or may not) have overdone it, but the code requirements needed updating. Remember that Northridge was an 6.8 or 6.9. The region will someday see an 8.0 or 9.0. Thats a 1000 or 10000 times greater energy release than Northridge.

Northridge demonstrated that the then-existing code was insufficient to prevent major loss of life, or major economic collapse, when (not if) the "big one" finally manifests itself.

________________________


A comparable argument was made that Dade county lost their minds with all of their wind-related code upgrades. Subsequent hurricanes have tested te newer code constuction and have demonstrated the wisdom of the decision.

[Bill Robinson]

Correct me if I'm wrong, but it appears that death in single-family homes was a non-issue, as there was very little damage and most of that was cosmetic. It seems the death and property damage occured in commercial buildings built on "soft-front" foundations such as parking garages.

Stand corrected, there were a few deaths, how few does it take to be a non-issue?
Add to that the structure damage ( a very large amount, ask the insurance companies and the folks in Filmore) and loss of use from the the earthquake and you have a parade. Or a need for improvements.
Isn't code the minimum requirement?
Barely legal building?
How much general welfare do you want?

Still not sure of your point here.
Earthquake Bill