Case of the month: house cracks

Jun 3, 2012 by

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.

Our expert inspected the structure in the presence of the insured’s son. The property was located in a high desert community and was at, or near, the top of a slight hill (elevation approximately 3,000 feet) on the street. There was a depression in the rear yard like that of a wash. The building was a single-family, timber-framed structure, aligned principally east-west on the north side of the road, with an attached garage to the west. The rear yard was largely dirt with a concrete patio adjacent to the building, and a timber stairway led to the roof deck. The insured’s son stated that the cracking had been progressing in the front yard under the driveway. In the rear bedroom, there was a lump under the carpet. He was concerned by cracking and bowing of the front of the building. The expert took a series of photographs of the site for inclusion in his report.

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.

This was consistent with downward ground movement under the supporting framing to the wall. There were cracks in the stucco coating to the exterior of that same wall that were also consistent with downward movement and possible bowing of the exterior wall. The floor of the bedroom was slab-on-grade concrete. The concrete has cracked and was bulging upward into the room. The driveway had cracking both laterally and longitudinally.

The concrete of the driveway had reinforcing steel mesh, as measured with a rebar locator. The location and direction of the driveway cracking was not consistent with the more random or diagonal pattern of root incursion under the driveway that may be caused by tree roots. The nearest tree roots to the driveway were not shallow enough, nor were they strong enough, to cause the damages seen. The nearest tree was of the species Sambucus which does not have an aggressive root structure, according to the “Complete Trees of North America” by Thomas S. Elias.

The cracking to the support post in the front of the building, supporting the roof over the porch, had horizontal cracking, consistent with downward movement of the supporting foundation concrete and dirt. The downward bowing of the eaves at the front of the building was also consistent with failure of the support structure at the corner. There was no indication in the United States Geological Survey (USGS) records of seismic activity that would have resulted in the movement observed in the rear bedroom, the front driveway, nor the front porch structure.

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.

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