Residential Renovation: Design & Construction Defects

portrait photo of Jeffrey

Jeffrey W. Pitzer, P.E.

“A good intention, with a bad approach, often leads to a poor result" - Thomas A. Edison

EDT was assigned to determine the cause of damages to a single-story residence. The residence, constructed in the 1950’s, was renovated in 2015. The work consisted of a complete teardown of the structure and cladding. The replacement structure was constructed on the existing timber floor beams and concrete perimeter footing. The interior floor framing beams were supported by wood columns on concrete piers set on the exposed soil about 30 inches below the floor resulting in a crawl space. 

The remodel included replacing the grass lawn with artificial turf and a sprinkler system at the front of the residence for plants and foliage.  Raised wood decking was constructed along one side and gravel at ground level was placed along the opposite side and rear of the residence. Drip line irrigation was placed along the perimeter of the residence. 

Downspouts from the gutter discharged into enclosed underground drains. 

About two years after the renovation was completed, the flooring deflected and the homeowners began to experience health problems related to air-borne bacteria. 
A contractor was engaged to remove portions of the flooring to access and examine the condition of the framing in the crawl space. 

Figure 1
Figure 1 - Flooring removed to provide access to the crawl space

With appropriate personal protection equipment (PPE), examination through the access holes showed numerous portions of the timber beam framing were decayed with the majority of the decay located adjacent to the perimeter foundation.  There was significant fungal growth on the lower face of the wood floor decking.

Figure 2 – Crawl space with concrete perimeter footing supporting timber beams
Figure 2 – Crawl space with concrete perimeter footing supporting timber beams
Figure 3 – Fungal growth on underside of floor beams and flooring
Figure 3 – Fungal growth on underside of floor beams and flooring

The timber beams that terminated at the perimeter foundation were set in notched portions of the concrete foundation wall such that the top of foundation and top of the beams were at the same elevation. 

Figure 4 – Notched beam pocket in perimeter concrete foundation - candidate source of moisture intrusion.  
Figure 4 – Notched beam pocket in perimeter concrete foundation - candidate source of moisture intrusion.  

Cause of Moisture Intrusion and Resulting Biological Growth

There was no observed ventilation for the crawl space or vapor barrier on the surface of the soil in the crawl space. Crawl spaces require ventilation to allow moisture ingress from the soil or exterior grade to be removed. The original ventilation openings were covered during the renovation and sealed the crawl space. Portions of the grade along the perimeter were at or above the top of footing elevation and some of the grade sloped towards the foundation instead of away from the foundation. 

Exterior grade deficiencies resulted in portions of surface water runoff from rainfall, sprinklers, and drip irrigation to intrude into the crawl space at the notched beam pockets of the concrete foundation wall. 

The sloped grade that caused water to drain towards the foundation was a construction defect that resulted in water intrusion into the crawl space. The sealed ventilation openings were a design defect that prevented proper ventilation and resulted in an accumulation of moisture over an extended period of time in the crawl space that caused decay of the timber beams and flooring and an abundance of biological growth. The investigation by EDT documented and concluded that the damages resulted from long-term exposure to moisture caused by design and construction defects.

About the Author

Jeffrey W. Pitzer, P.E. is a consulting engineer with our Houston Office. Mr. Pitzer provides structural evaluation and inspection, damage assessment and repair of concrete foundations, steel buildings, structural framing and roofing systems for commercial, industrial and residential buildings and structures. You may contact Jeff for your forensic engineering needs at jpitzer@edthouston.com or (281) 463-4548.

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