The insured turned in a claim for damages to his residence. GEI was assigned to determine the causes of the damage and the approximate age. Specifically we were to examine four areas: cracking in the driveway, a lump under the carpet in the rear bedroom, bowing fascia board on the front of the property, and a bowing of the support for the roof in the same area.
The dirt surrounding the property was sandy to sandy-gravel and appeared well drained. The property itself was apparently first developed in, or about, 1972, according to the insured’s son. The building condition was consistent with a building of that age. The rear bedroom appeared to have been added after 1995, but prior to 2003, according to photographic timeline views of Google Earth. (No official records were examined.) He also noted that the deck on the roof was constructed in, or about, 2009. No research was conducted to verify the existence of a permit to construct the bedroom addition, nor the roof top deck. The rear wall (north wall) of the bedroom included windows, the headers of which were cracking horizontally.
Based on the foregoing, it was the expert’s opinion that the predominant cause of the damages seen was consolidation of the dirt under the property, consistent with excess water flow across or under the site, recalling that the dirt was well drained. The approximate age of the damages was consistent with ongoing movement of the earth or dirt under the property and appeared to have begun in excess of one year prior to the date of inspection.
While that answered our client’s questions of causation and age, you may wonder if this damage was preventable? Well, the damage was preventable and is not well understood by contractors and especially not by DIY builders. The existence of the dry wash in the back yard was a good clue to the likely presence of more silty soils than normal. This should have tipped the contractor to understand that those soils are more able to be compacted over time rather than just immediately upon laying of the slab (having a higher organic content than sandy soils – hence a soil matrix that would deteriorate over time). That fact would thus require a deeper foundation.
The typical foundation slab of four inches, with no edge thickening, is not sufficient to withstand this type of soils movement, and soils compaction would not have fully realized the goal of limiting movement. The time since the damage was discovered (after several years of no reaction) was another good clue to the deterioration of the soils over a long period. The extra weight of the back bedroom did not contribute significantly to the problem, but it did highlight the fact that building inspectors should always be prepared to require contractors to dig deeper below any possible interference of the silty desert soils, especially when two story structures are built.
Inclusion of mesh rebar in the slab would also have gone a long way to alleviating the “hump” found in the floor. An edge thickening of nine inches to twelve inches would have worked wonders for the stability of the slab, not to mention adding a small grade beam to the floor margins. Desert soils are odd ducks, subject to movement when one least expects it.