May, 2003
Inspection News and Views from the American Society of Home Inspectors

A Lesson in Basics: Foundation Inspections, Part 2


Continued from last month

Home inspectors inspect new to 100+ year-old basements, crawl spaces and slabs constructed of a variety of materials and placed on different types of soil. In some regions, foundations are for the most part similar. Differences region to region may be based on local climatological conditions. Nevertheless, the job remains the same – to report defects. As mentioned in last month’s foundation article, when I give a presentation on foundations, I start with the basics – a description of common defects and related conditions. Settlement; cracking, bulging and bowing; and slippage were covered last month. Material degradation rounds out my list of common defects.

Material degradation

Materials used for foundations degrade with time, particularly when exposed to the four alchemy elements – water, air, wind, and fire. Each has its own strengths and weaknesses.

Laid stone

Typically laid stone foundations are found in older structures (100+ years, mostly). Laid stone foundations are usually relatively thick – 18" to 2' or more. Most do not have footings, being wide enough to properly transmit the loads to the soil on which they rest. The stones may or may not be mortared. See Illustration A.


Illustration A

If the joints are mortared, check the condition of the mortar. Quite often the mortar is little more than crumbling sand. These joints should be pointed, not so much because they represent a structural concern (which they may), but because the porous joints provide a path for water, insects, and rodents to enter the basement areas.

Check also for evidence of bulging. Bulging is often caused by pressure against the foundation wall. Minor bulging may or may not be a cause for immediate structural concern; there may still be a sufficient amount of material available to provide structural support. Major bulging, as a rule defined as of more than about half the thickness of the wall, should raise a red flag. It may be necessary to rebuild the wall, and to create an engineered drainage system. Few older stone foundations were provided with perimeter or footing drainage systems, and many were not originally mortared.

Common brick

Brick foundations, as with laid stone foundations, are usually quite thick. They too are usually found in older homes. Common brick is often used for support columns, which are also a part of the house foundation system. See Illustration B.


Illustration B

When inspecting a brick foundation, check the condition of the mortar, particularly low along the foundation wall. Also, check the condition of the brick by probing it. Often the bricks begin spalling, usually low along the wall. Severe spalling and/or mortar degradation may require corrective measures.

Brick degradation, particularly in older structures, is often the result of using under-burned bricks. Because under-burned bricks are softer than other bricks, they tend to absorb moisture more readily, and to degrade more quickly. In my area of upstate New York, bricks date as far back as the late 1600s.

When brick foundations are not fully visible, I have no way of knowing the condition of the bricks. With brick foundations, I recommend using prudence and judgment as your reporting guide.

Block walls

Block walls, either cinder block or newer concrete block, seem to hold up well. I’ve not seen a lot of material degradation with block walls (as yet). I have seen problems from cracking, but the cracks are generally caused by external problems – hydraulic pressure.

Block walls, however, are more porous than concrete walls, and they usually have cavities within the blocks. Problems can occur if the outer surface of the wall was not properly damp-proofed with an asphaltic coating. As water slowly seeps into the blocks, the cavities can become partially or completely filled with water. You may see evidence of this water seepage in the form of efflorescence on the block surfaces, usually low on the foundation wall.

Efflorescence is mineral salts left behind as the water evaporates from the block surface. The mineral salts come from the soil outside and also from the materials used to make the block being dissolved by the “universal solvent” – water. I don’t have a handle on the nominal lifetime of block walls at this time.

Wood destroying organisms pose another potential problem with block walls. The top course of a hollow block foundation wall should be a 4" thick “termite block.” If there is no termite block, the cavities of the top course should be filled with mortar. If possible, check for a solid top surface.

Poured concrete

Although in my experience material problems are not common with poured concrete walls, shrinkage cracking does occur. Also, as with other foundation materials, poured concrete walls are subject to external forces. Concrete is strong when being compressed, but not so strong when being stretched (in tension) – it is brittle and can snap like a pretzel stick when it is stretched or bent. That’s why steel reinforcement is typically used inside concrete walls. Unfortunately determining the presence, amount, or absence of such reinforcement requires special equipment, and is not in the scope of a typical house inspection.

Below grade wood foundation walls

Wood foundation walls are rare in my region. I’ve only seen one since I started inspecting in 1984. The key to the success of such a system is impeccable attention paid to drainage. Unfortunately, unless you were there during the original construction, confirming adequate drainage is impossible. About the best you can estimate with pressure treated lumber is 30-year ground contact rated. Although others may disagree, I believe that’s enough said about material degradation of this product. See Illustration C.


Illustration C

Footings and frost heaving

Sometimes foundation problems can be traced to being placed on footings of less than the proper depth. In warm climates, such as Florida or Southern California, this may be of no concern. In colder areas where the ground may freeze, frost heaving can occur. See Illustration D. Figure 1 also shows an example of frost heaving. In this example, the problem was in a garage in a rural area where building inspections were generally non-existent. The garage floor edges were poured thicker than the floor slab, but not deep enough to be below the frost line.

Basement floor cracking

In my opinion, floor cracking is a foundation problem, and support columns are part of the house foundation system. Floor cracking can be an indication of settlement as it relates to the entire foundation system. See Illustration E.


Illustration E

Should you see a basement with a poured concrete floor and one or more columns supporting bearing beams with circular cracks in the floor, with their center located at the column, you can be almost sure that the pier is settling and the floor is following it.
You may also see cracking of a generally circular nature in a basement or a garage when excavation was filled with soil and not properly tamped before the floor was poured. In severe cases, the un-tamped soil beneath the slab has settled enough that you can hear a “hollow” sound when the floor is tapped with a hammer.

Inspecting foundations

Is the defect severe? Is it stable? Does it require further evaluation? Has this two-part overview of four categories of common foundation defects – settlement; cracking, bulging and bowing, slippage and material degradation – helped prepare you to answer these questions for your clients? Better yet, has this two-part overview convinced you of the complexity of the topic, the need to know more, and the wisdom of recommending the services of engineers or foundation repair experts under certain circumstances? If a house is only as good as its foundation, this part of the inspection is important. I’ve found there is always something more to learn about foundations, and hope you agree. If you have comments, please e-mail me .