Inspecting Structural Components

 Inspecting foundations can involve tough calls.  Like most home inspectors, I am not an engineer, so I am neither technically qualified nor licensed to say whether something is structurally adequate.  But the foundation is a major component of any home, and I need to give clients some guidance, especially when they are dealing with an older one.  I rely mostly on my experience repairing and replacing foundations as a general contractor.  Following is an outline of how I approach it.  For illustrations, go to this Picasa album (you will not need to register there) : 

First, I try to determine what kind of foundation I'm dealing with.  I say "try" because it is not unusual for a foundation to be concealed by a basement remodel, a coat of plaster, or the owner's collection of old newspapers.  To some extent, the type of foundation can be predicted from the age of the house.  In the Bay Area, homes built prior to about 1908 commonly have brick foundations unless they have been upgraded.  From then up to the late 1920s or early 1930s, most homes had concrete foundations, but these foundations did not contain reinforcing steel, were much smaller than modern foundations, and were often poorly mixed from local materials.  These are called "batter board" foundations in the trades because of the characteristic shape -- a result of the forming method -- with a sloping face on the interior and a vertical face on the exterior.  In the 1930s to 1940s -- the timing varies by area and also by the market the house was built for -- builders started using better concrete, better designs, and a certain amount of reinforcing steel.  Many of these foundations have held up quite well.  Starting in the 1950s, foundation design and installation methods took essentially the form in use today.  One exception is foundations for difficult sites such as steep hillsides, where the use of deeply drilled piers has been perfected in more recent decades.   

Once I know the era, and if I can establish that the foundation has not been changed, I start looking for conditions typical for the vintage.  Brick foundations are the easiest "call" because it is generally (though not universally) agreed that masonry will not stand up to a strong earthquake and that there is no reliable way to anchor a building to it.  Except in the finest vintage buildings, brick foundations were almost always quite small, barely extending above the soil. They are usually deteriorated due to moisture.  It is almost always a no-brainer to call for replacement.

Things get a bit trickier with the early concrete "batter board" foundations. A common defect in  these foundations is that the walls are supported on the outer edge of the shallow foundation.  With time, the off-center weight has often caused all or part of the foundation to tip outward -- a condition called "rotation."  Symptoms of rotation often include cracks near the corners of the house and a bulge or distortion of the exterior wall just above the foundation.  If rotation is  bad enough, the lower walls will be out of plumb and support is clearly compromised.  Like nearly any kind of foundation, these were also susceptible to failure due to poor soil compaction, drainage problems, and other underlying conditions.  Problems in these foundations tend to be worse on sloping lots, where the downhill portion may not be deep enough to rest on competent soil. On the other hand, there are thousands of these foundations that are still adequate.  The key criterion is whether they are stable enough and the concrete solid enough to permit anchoring the house to them.  If a foundation of this type is generally intact, without excessive cracking or rotation, and if the house has not been significantly altered, I am pretty conservative about calling for replacement.  In most cases, it is more urgent to reinforce the house to resist the "big one" -- which can wreck the house in 2 minutes -- than to worry about a foundation defect that may take decades to cause a serious problem. 

Certain defects can appear in almost any type of foundation, old or new.  One of the most common is that it does not exend far enough above the soil to prevent moisture from reaching the framing and causing decay.  Sometimes this is due to construction error, sometimes to changes in grading and landscaping that have raised the soil level next to the house.