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STRUCTURAL INSPECTIONS & DEFECTS
ADVANCED INSPECTION METHODS
STRUCTURAL INSPECTIONS & DEFECTS
Home inspection methods: this free online class presents advanced building inspection techniques to improve the detection of subtle clues and to enable more accurate reporting of difficult-to-detect safety or costly defects in the system or building being inspected. These home inspection methods use a strategy and suggest methods which may be useful in the inspection of any complex system for defects. CONTACT us to suggest changes or additions to the text.
We discuss methods to improve the inspector's ability to "see" defects, even those for which there may be no immediately-obvious visual evidence. We discuss methods of accumulating evidence about the condition of a building (or any other complex system being examined) in order to cross thresholds of reporting, action, or determination of the level of importance of the evidence found.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Advanced Home Inspection Methods - Classes & Levels of Fear, and how to use them to find and report significant, hidden problems in the inspection of buildings or other complex systems
Daniel Friedman - Poughkeepsie, NY 12603 U.S.© 2013-1997 all rights reserved
We also discuss, and link to a more detailed article about the nature of vision and the human ability to "see" and to "notice" visual information, and we suggest strategies to improve the ability to "see" during inspections. This is an continuing-study topic and will be revised frequently. (08/31/2007) A power point classroom presentation of this paper can be read online at InspectAPedia.com/structure/x-ray-ppt.htm. In the photograph above, the severe damage to this building is obvious. The source of the damage is probably obvious too - leaks at a roof valley.
But the conditions that led to this severe damage and ultimate collapse of portions of a valuable historic (but unattended) building could have been spotted decades before. The damage could have been prevented by a minor repair.
Introduction: Dealing with "Hidden" Defects in the Inspection of Buildings or Other Complex Systems
Updated 3/8/2013 - priorities & maintenance
What about "hidden" defects? What is hidden? If an inspector didn't observe [and report] a defect, it remains "hidden," in a practical sense since no action will be taken, regardless of how much direct, visible evidence was actually available.
The methodology discussed in this paper applies both to truly totally hidden defects and to those which were perhaps perfectly visible but which are "missed" by the observer. An inspector couldn't/didn't get up on a low-sloped rear dormer roof which is later discovered to be totally worn out - a condition which might have been predicted from the ground whether there was ready access for him to see it or not.
An inspector fails to explain in her report that evidence of a history of water entry in a finished, paneled basement means that there is a high risk of hidden mold, insect damage, or rot. Failing to provide this explanation of a field observation can leave a costly and potentially unsafe mold hazard or hidden damage in the building. It is "hidden" from the client even though there may have been overwhelming evidence of its presence.
Superman has X-ray vision. But even if he could see inside building components, would he understand the implications of what he was observing? Pretty nervy, talking about obligating us to report hidden damage! Can we really address serious problems for which there is no visual access? Should we? We don't promise to deliver real X-ray vision. We use something that may look like X-ray vision where we can to find faults which may otherwise go unnoticed or "hidden."
Discussing the detection of so-called "hidden" defects strikes fear into the heart of home inspectors.
It brings confusion to the legal profession.
It incites rage in the hearts and lungs of realtor - perfectly decent folks whose legal and contractual obligations to building sellers put them naturally in a position of conflicting interests with those of a property buyer. In other words, just slip your check under the door. Very close, thorough, detailed, building inspections make some folks nervous. This need not be so; it is unusual for even the most expert building or home inspection to discover defects which are so costly to cure that the purchase should be called into question.
Reading this paper or attending this lecture makes a tougher approach towards finding hidden defects part of our professional literature and thus raises the standard of due diligence for all of us. If you don't want to practice at this level you should stop reading this material or if you're seeing this in a classroom, leave the room now.
This topic divides home inspectors into camps: the ostrich camp (if we can't see it I'm not responsible for it and shouldn't have to even think about it), and the investigative camp (if there is a dangerous or costly problem for which we might find evidence and issue a warning we owe it to our client to do so).
For home inspectors, the fear is that if clues, even subtle ones, exist for a defect, we may be expected to find it. That's why it's difficult. Unlike a forensic engineer, we don't get to order destructive testing. Whichever camp is your tendency, better investigative skills can only improve your service to your clients and reduce risks for all.
This section of this paper has now been published as a separate article found as vision.doc and online as http://InspectAPedia.com/vision/vision.htm - The Nature of Vision - inspecting complex systems
Let's look briefly at some underlying theory which will empower inspectors to see and think more forcefully and perceptively when they are in the field. Then we'll test the theory with actual practice. Finally, we'll see what conclusions we can make about how we might wish to modify our inspection practice.
A natural, careful program? Sounds far too orderly! Home inspections are chaotic. There are people, control, and technical issues! Clues are often discovered randomly with respect to space and time.
Provided the inspector understands possible implications, provided the inspector maintains an inquiring mind, randomness is a help not a hindrance. It constantly presents fresh data, keeping the inspector alert for important information.
Randomness prevents the inspector from becoming routinized - an automaton which always sees, says, reports the same items is guaranteed to miss many costly and dangerous problems whose clues lie outside the habitual automatic range of action and thought.
The right attitude is essential. Cookbooks don't work. Checklists are incomplete. High-speed run-throughs cheat both the consumer and the property. Every house has a unique surprises. Look for them. Stay open to new, unfamiliar possibilities at every house. That's how to maximize the chance of discovering as much as possible about the property. Don't' assume! The last explanation for a familiar anomaly may not be correct this time.
Little clues can point to hidden (or previously undiscovered) problems. Collect them.
Clues may be small visual anomalies, historical information, smells, sounds, both familiar and unfamiliar.
A small anomaly may defy understanding. That's ok. 
The most powerful clues are often simply construction practices which are known to lead to trouble.
If an anomaly doesn't lead to something, just keep it on mental file for a while.
Looking carefully at any complex system will produce a large volume of clues.
A large volume of clues will usually produce a large volume of "findings" or "defects."
This large volume is distracting, confusing, and makes for trouble for everybody.
Let's take a look at how to respond to these characteristics by seeing how we should respond to the difficulties cited above, and to sometimes subtle, context-dependent, or important but obscure building inspection clues.
Before you can start contemplating details, how do we deal with the signal-to-noise ratio problem?
That is, how do we select among the thousands of details available?
1. Stay away from unimportant details even if they "impress the client" (like testing stove burners) - they can cost big-time by diluting attention. An expert should sort detailed observations into clues that may justify further investigation and those that can with confidence be classed as a terminal point for an unimportant finding. For example, is a stain seen on a wall due to a hidden leak or due to soiling from a pet who rubbed against that area?
2. Avoid Selection Errors - making a mistake about which details get attention. Focus on the center of the large field of an easily-viewed steep-slope roof having no penetrations and in good condition should not be at the exclusion of a low-slope hard-to-see roof more likely to be worn and leaky.
3. Choose your focus based on the return on investment of your time and your client's money. Time spent assessing clues that suggest costly hidden problems is more important than time spent testing stove burners or determining which water lines are controlled by which shutoff valves (other than identifying the main shut-off).
If the clue (or actual defect) is likely to be connected to costly or dangerous findings, it should be pursued. If it is likely to be a dead-end, it should receive minimum attention. Why? Because the quantity and quality of your attention are limited and absolutely must be properly focused. 
This is what most competent inspectors actually do:
1. make observations
2. consider implications
3. evaluate interactions among components and systems
4. weigh risks and probabilities of a potential defect - levels of fear
5. collect more data which increases or decreases level of concern (fear)
6. continue until the observations (fear) force the defect across thresholds of reporting
7. make recommendations
As thresholds of reporting are crossed, report or act appropriately:
1. Lowest: consider but do not report - premature, keep the observation in mind and continue inspecting
2. Medium: report potential defects to client with advice: watch, investigate
3. High: report likely defects to client and advise further action
4. Extreme: report or find and identify virtually certain costly or dangerous conditions
Contextual clues, subtle little defects, visual or other anomalies, modifications, historical data, and site conditions may later suggest the presence of a costly or dangerous problem at probability high enough to justify a warning to the client even when there is no unequivocal, directly visible defect. (Example: very rusty old furnace in basement showing history of recurrent flooding, high risk of failed heat exchanger. Dangerous. Investigate further, reserve funds to replace unit.)
There is considerable argument among building inspectors about whether or not the inspector is obligated to report important building defects that are recognized by inference rather than by obvious simple visual data. We inspected a house with no accessible crawl space, a history of roof spillage around the foundation, trees close to the house, wood siding and framing below grade, and a bulged first course of aluminum siding all around the home. Anyone familiar with how aluminum siding is placed on a building knows that you start from the first or bottom course and hang siding up the wall. There is no way you could install a bulged first course. The bulge had to happen later - in this case from building settlement on crushing, rotted, or insect- damaged wood sills and floor framing. Yet outside there was no visible evidence of rot or insect damage to the house sills, since they were not visible (without invasive measures not part of a normal home inspection.).
The realtors present at this case study, and some of the building inspectors all argued that since one could not personally see a framing problem, there was nothing that should be reported. This camp argued that reporting a costly building damage condition was mere speculation.
I agree - that it is speculation, but I'd call it "informed" speculation. If the collection of contextual clues crosses a sufficient threshold of risk, such items should be reported. And of course, as most readers will suspect, later removal of siding showed very extensive sill and floor joist framing damage from termites and rot. At $100./linear foot just for sill repairs, this was a very costly problem that needed to be brought to the attention of the building buyer and owner.
Weigh the risk of angry realtor who feels that you should not be thinking so carefully about hard-to-see defects, or embarrassment of being mistaken by warning of a potential hazard against the risk of someone's injury or in the case of collapsing septic and cesspool systems, dangerous chimneys and flues, carbon monoxide and combustion air problems (can't see that one can you?), or even mundane falling hazards, there is risk of serious injury or even death!
How do we cope with the quantity of details which present themselves? Focus attention on the high-risk topics.
Here are the classes of findings which deserve highest priority of attention. This little list can help the inspector and the inspector's client sort through the large volume of clues and "findings" that will be produced by any careful inspection of a building. For the following three items, the "building is in control of the client's money" in the sense that items in all three categories really need to be addressed promptly.
1. Things that are Dangerous 
2. Things causing rapid, costly Damage
3. Things that are essential that Don't Work 
Maintain this focus. Distinguish between what is potentially important (costly, dangerous, doesn't work) and what is not only unimportant (on a cost and risk scale), but can be a dangerous distraction. Don't waste energy, and don't mislead your client by permitting the client to think that the purpose of your inspection was to find defects.
Correcting other defects may be highly desirable, may make a building more economical to operate, or more comfortable, but they may be elective in that the client can decide when these expenses are to be incurred.
If a building has no insulation, the inspection and report need to point that defect out, and significant cost may be involved in its remedy. But delaying the installation of insulation means higher heating or cooling costs, not that the building is suddenly unsafe or deteriorating rapidly (excluding the freezing pipe problem in freezing climates). So this is an example of an item which, while important, can be deferred.
You may point out minor defects, as a courtesy or even as an added service, but keep yourself and your client focused on the purpose of the inspection: to reduce the chances of a costly or very dangerous surprise. Otherwise both you and your client will be very sorry later. Explain this focus to your client.
Isn't this what you're already doing? Then why talk about it?
Case studies show that serious defects are sometimes are discovered by a small triggering clue. Some would have been discovered anyway, some possibly not.
1. What did you find?
2. What was the first clue?
3. How did you follow it to a conclusion?
4. How glad were you that you found it?
1. What did you miss?
2. How was it later discovered?
3. How sorry are you that you missed it?
4. What could you have seen or thought that might have permitted an accurate guess, warning, prediction?
We can develop a very simple methodological way of thinking which is helpful without making us routinized. This paper uses mini-case studies of visible conditions to suggest interactions among systems and therefore likely areas where serious defects may be found.
Don't bother memorizing the specific case study conditions which follow.
The objective is to develop a way of
1. Thinking [the "Zen" of inspecting complex systems]
2. Seeing [the nature of vision for complex systems]
3. Thinking further [the promotion theory for inspection clues]
4. Investigating further [thresholds of action for inspection conclusions]
5. Concluding [a decision of the level of risk involved and an opinion of the need for action]
6. Advising [further investigation, repair, or notification of an immediate hazard]
to substantially improve the quality of a professional inspection by reducing risk for both the client and the inspector.
Inspection performance can be substantially improved, adding value and reducing risk to all parties.
Techniques can improve visual detection of defects present on the system being examined, reducing inattentional blindness by a variety of methods
Techniques for focusing vision and avoiding distraction can improve visual detection of clues suggesting "hidden" defects
Methods of thought regarding collected clues can improve the accumulation of evidence, the promotion of possible to probable defects, and thus recommending appropriate action
Regardless of views about inspecting and reporting limitations expressed by inspectors, few clients would find acceptable an inspector who indicated that regardless of the possible implications of external evidence the inspector intends to refuse to warn about costly or dangerous hidden damage for which there was less than full clear visible evidence.
It should be possible for each inspector to significantly improve his/her field performance by making an ongoing study of those cases where a costly or dangerous defect was identified "just barely" or with difficulty.
Scrutinize your inspection process:
What is the significant finding that we made?
What was the very first clue that got us thinking about it?
What did we think then?
What did we do next?
How did we collect and correlate information?
When did we first understand that there was probably a serious defect?
What additional clue, observation, thought led us to that conclusion?
What additional information was we able to collect?
How did we find and correlate it to come to a final identification or other conclusion that this was, or was not, a significant concern?
In sum, what small anomaly did we observe that led to an important conclusion?
This approach by no means suggests that you cast out more strict and methodical investigative procedures. Checklists and procedures are most helpful for determining that something is missing, or that you've left something out. But no inspection checklist, no procedural guideline, can ever possibly cover every anomalous condition nor every possible major defect that may be present at a property.
We should always be asking: what's different here? What surprise is waiting? What's holding that up? How do air, moisture, people move in the building? How does that work? What was changed here? Why did they do that? Did it work? What did we later find out we missed at an inspection? How could we have seen it?
Addendum: Background thoughts behind inspection methodology:
What is the nature of the most valuable possible advice to a client regarding property condition?
- It is as complete as possible within the limitations of the process
- It is as accurate as possible both in conclusions and advice
- It is as reasonable and economical as possible both in priority and level of attention and repair.
Researchers are concerned about Type we Errors and Type II Error. Or: the error of accepting a false hypothesis and the error of rejecting a true hypothesis.
Most inspectors think about the error of rejecting a true hypothesis.
A true (in this instance) hypothesis: "the fire chamber is leaky and dangerous."
An erroneous rejection of a true hypothesis:
"The furnace is new, we don't see any rust, so the fire chamber is ok."
- burn marks on back of furnace jacket where flames escape a crack caused
during shipment - the confident inspector didn't look at all sides of the unit.
Why was this observation missed?
- assumption error (new equipment)
- attention error (tired inspector)
- distraction error (irksome realtor, client, kid, dog, owner, parent)
- inaccessibility - (but might the inspector have noticed something like a crushed cabinet corner that might have raised a question?) Here's "X-ray vision!"
Adverse Selection: Borrowing from the Insurance Industry - Making Safe but Bad (for the Client) Recommendations
Adverse selection of choices - when a consultant gives advice to the client in a manner which benefits the consultant (minimizing his risk or maximizing his income) rather than in a manner which most benefits the client (appropriate expenditures based on risks and probabilities).
Client makes the inspector nervous
Inspector knows s/he is not informed on a given topic
Inspector is a novice, knows it, and is afraid to show ignorance
Inspector is worried about hidden damage
Contractor takes the safe, profitable choice: replace all rather than fix
So the inspector recommends that a component be replaced, or that costly destructive inspecting be performed, when it's not necessary and not appropriate. The cost is a misapplication of both attention and money on everyone's part.
Engage in real risk management rather than simply giving advice that is intended to protect the inspector at the client's cost.
We cannot reduce risk to zero. To attempt to do so would be to tear everything apart, replace everything, and in the course of reassembly, make new errors which would lead to still more problems.
We identify visually detectable problems, visually detectable risks for which there is sufficient data to suggest attention, and selecting levels of response appropriate for economic and safety reasons.
How can we push risk reduction further in a cost-effective way?
First, why should we work to further reduce risk?
Reducing risk for the client adds value to the inspection - it's good business.
Reducing risk for the client reduces also risk for the inspector.
We can substantially reduce risks of major costly or dangerous surprises. Estimates of payback at any competent inspection, comparing fee to the dollar-cost of previously unknown repairs plus the cost of savings accruing from early recognition of those topics range from 10:1 to 1000:1.
Second, how can we push risk reduction further, cost effectively?
Improve professional competence, learn details of construction, systems, failures, repairs, proper practices.
Improve inspection technique, practice methods which develop skill at recognizing problems
Numerous other topics (see end of this paper).
One technique for risk reduction: develop proper inspection focus
Home Inspection Case Studies Contextual Clue Detection, Interpretation, & Defect Reporting
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The frost heaving forces developed under a 1 ft. (30.5 cm) diameter steel plate were measured in the field throughout one winter. The steel plate was fixed at the ground surface with a rock-anchored reaction frame. heave gauges and thermocouples were installed at various depths to determine the position and temperature of the active heaving zone. The general trend was for the surface force to increase as the winter progressed. when the frost line approached the maximum depth the force was in excess of 30,000 lb (13,608 KG). Estimates of the heaving pressure at the frost line ranged from 7 to 12 psi (0.49 to 0.84 KG/cm) square during this period. The variation of surface heaving force was closely associated with weather conditions. Warming trends resulting in a temperature increase of the frozen layer caused the forces to decline.
Leda clay slopes in the Ottawa valley are vulnerable to catastrophic landslides. More than 250 landslides, historical and ancient, large and small, have been identified within 60 km of Ottawa. Some of these landslides caused deaths, injuries, and property damage, and their impact extended far beyond the site of the original failure. In spectacular flowslides, the sediment underlying large areas of flat land adjacent to unstable slopes liquefies. The debris may flow up to several kilometres, damming rivers and causing flooding, siltation, and water-quality problems or damaging infrastructure. Geologists and geotechnical engineers can identify potential landslide areas, and appropriate land-use zoning and protective engineering works can reduce the risk to property and people.
Deposits of Leda clay, a potentially unstable material, underlie extensive areas of the Ottawa-Gatineau region. Leda clay is composed of clay- and silt-sized particles of bedrock that were finely ground by glaciers and washed into the Champlain Sea. As the particles settled through the salty water, they were attracted to one another and formed loose clusters that fell to the seafloor. The resulting sediment had a loose but strong framework that was capable of retaining a large amount of water. Following the retreat of the sea, the salts that originally contributed to the bonding of the particles were slowly removed (leached) by fresh water filtering through the ground. If sufficiently disturbed, the leached Leda clay, a weak but water-rich sediment, may liquefy and become a 'quick clay'. Trigger disturbances include river erosion, increases in pore-water pressure (especially during periods of high rainfall or rapid snowmelt), earthquakes, and human activities such as excavation and construction.
After an initial failure removes the stiffer, weathered crust, the sensitive clay liquefies and collapses, flowing away from the scar. Failures continue in a domino-like fashion, rapidly eating back into the flat land lying behind the failed slope. The flowing mud may raft intact pieces of the stiffer surface material for great distances.