Slab on grade construction can be completely invisible to the home inspector. The outside edge of the slab is often finished with stucco, brick, or some other covering. And the surface of the slab is normally covered with subflooring and finish flooring.
First, the home inspector should make sure that the
construction method isslab on grade. What appears to be a slab on grade may be a concrete floor resting on piers and beams or simply grade beams. Ask the homeowner if there is some doubt on this point.
Even though the slab is not visible, there are signs that the home inspector can look for when determining the condition of the slab.
• Settlement: The home inspector should try to determine if
the slab has settled. Just as with any other foundation, soil can be washed away beneath the slab. There can be
problems at the corners with downspouts and splash blocks, causing the slab to settle unevenly. Heaving soil under the slab can cause the slab to tilt or sink, even twist and skew . Settlement can be caused by a leak in the plumbing or heating system embedded in the slab, which undermines the soil below.
Watch for cracksin the exterior foundation (stem) wall and
the slab itself. Even exterior cracks may not be a reliable sign, since they may only be in the stucco finish. But noticeable cracks on the interior floor can indicate settlement. Cracks in the slab are not likely to be visible. But even when the floor is covered, cracks can sometimes be felt under foot or seen when a flashlight is used to side light the floor.
• Shifting: Slabs can shrink and pull away from the outer
wall if not properly attached during construction. T he slab can crack along the wall perimeter. As a result, shreds of slab may be left on the wall where the slab has become detached. The home inspector may find cracking along the floor edge.
• Moisture: The home inspector should report evidence of
water penetration through the slab. Moisture can come up
Guide Note
Pages 70 and 71 present a discussion on inspecting slab construction. You may want to go back to pages 19 and 20 of this guide to review slab on grade construction techniques before reading this short chapter.
into the house through cracks in the slab or through the openings in the slab. During the inspection, the home inspector should pay attention to these openings, such as plumbing lines coming up under the sink. These openings are places where moisture and insects can come up from the soil into the home. Moisture along the edge of the slab can indicate the slab has broken away from the foundation. When the slab and foundation sinks and settles below grade, water penetration can be a constant problem. • Post-Tension Cables: Post-Tension Cable ends can rust if
exposed to the weather. Verify that the concrete plugs over the cable ends are intact. If the cable ends are visible or rust is present be sure to note it in your inspection report.
Reporting Your Findings
Customers should understand that visual inspection of the slab is not possible. Explain that you’re looking for evidence
that something may be wrong with the slab, but that situations could be developing that are not yet apparent.
• Not visible: When you’re reporting on slab inspection, it’s
a good idea to be able to check of f a not-visible box every time.
• Slab condition: Note if you’ve found signs of settlement,
cracks in the slab, and the presence of moisture or water penetration.
DON’T EVER MISS • Cracked, shifting, or
settling slabs
1. Which statement is false?
A. The home inspector is required to enter the crawl space when possible.
B. The foundation walls of the crawl space do not have to be inspected.
C. The supporting structural members visible in the crawl space should be inspected. D. The home inspector should report the
method of access used to observe the crawl space.
2. Ceiling insulation in a crawl space should be installed:
A. With the moisture deterrent layer down. B. With the moisture deterrent layer up. C. Either way.
3. Perimeter venting is required in a crawl space to prevent:
A. Heat accumulation.
B. Insect penetration into the crawl space. C. The air from becoming stale.
D. Moisture from rising into the house. 4. In Photo #41, what may happen because of
the floor condition?
A. Foundation cracking and settlement B. Footing failures
C. Rusted piping and rotting in structural members
D. All of the above
5. What is not a likely cause of slab settlement? A. Shrinkage of the concrete slab
B. Faulty downspout and splash block C. Soil washed from beneath the slab D. Leaking heating system in the slab
6. What can be a sign of slab detachment? A. Moisture under the sink
B. Cracks in the foundation C. Cracks along the slab edge
7. Case Study: You enter a crawl space from an
entrance at the south end of the house to find a very uneven dirt floor. The entire north half of the crawl space is piled so high with dirt, you cannot inspect it. You find step cracks in the adjacent walls at the southeast corner. The cracks are displaced over 1/2”. There is a vent visible in the south wall.
What comment would you make in the inspection report about the north half of the crawl space? A. Area not visible, did not inspect.
B. No vent present in this area.
8. For the case study above, what comment would you write in the inspection report? A. Recommend evaluation by engineer B. No unusual cracks or movement apparent 9. In the case study above, what suggestions
should be made to the customer? A. Level the floor.
B. Cover the floor with a vapor barrier. C. Check for operating vents in the areas currently not visible.
D. Check the downspout and splash block in the southeast corner.
E. Have someone look at those cracks. F. All of the above
10. What condition could be listed as a major repair in the inspection report?
A. The ventilation situation B. The step cracks