Our scope of work was to perform a visual observation of the existing dwelling structure to assess its structural integrity. We performed our observation on April 23rd, 2019.
The 1987 condominium structure is a 2-story wood framed structure (condo address #101 is the upper level condo; a different condo unit below). The building is supported on continuous turn-down concrete foundations. A structure of this age has plywood shear walls for the lateral resisting system. The roof framing is conventionally framed with 2×6 rafters, roof purlins, purlin struts, and ceiling-ties.
Structural Observations of Suspected Structural Deficiencies
The observations listed below are suspected structural deficiencies related to the structural integrity of the house. Relevant photos are provided. More photos are available upon request.
1. The floors in the kitchen slope downward to the wall dividing the kitchen from the living room. The maximum slopes in these rooms are at 5/8inch in 4 feet across 8foot span; approximately 1.25inch total vertical displacement at the kitchen cabinets along the wall that divides the kitchen from the living room.
2. Interior drywall cracking occurs at the wall separating the kitchen and living room.
Photo 2A: Dry wall cracks at left hand side (facing kitchen from living room)
Photo 2B: Other dry wall cracks at left hand side (facing kitchen from living room)
Photo 2C: Dry wall cracks at left hand side (facing kitchen from breakfast nook)
3. Interior door frame is skewed between kitchen and living room. (Slopes down to left)
4. Interior drywall cracking occurs at the ceiling in the master bedroom.
5. Interior drywall cracking occurs at the fireplace wall in the master bedroom.
6. Interior drywall cracking occurs at the ceiling in the living room. (no photo available)
Assessments of Items 1 through 3
Items 1 through 3 were caused by a sagging beam recently installed by the condominium owner’s contractor in the unit below. While this beam was designed by a licensed engineer, the beam does sag creating the indications of structural movement described above. Most likely, the engineer designed the beam to satisfy the minimum code prescribed deflection limits in the current California Building Code. However, these are only minimum limits. To avoid the negative impacts to the subject condo unit, the beam could have been designed to a tighter deflection tolerance limit (beyond the code prescribed minimum limit) which would have resulted in negligible deflection impacts to the condo unit above.
The load bearing wall the beam replaced was also a lateral shear wall. However, the engineer designed a Simpson Strong-Tie Strong-Wall at both ends of the beam to absorb the design shear forces which would have been transmitted from the diaphragm into the previous shear wall. Based on our brief review of these drawings, the concept the engineer provided is appropriate.
The foundation design under the previous load-bearing/shear wall showed an expanded foundation to accommodate the new vertical forces transmitted from the new posts (supporting the new beam) and the new Strong-Walls. Based on our brief review of the drawings, the concept the engineer provided is appropriate.
Assessments of Items 4 through 6
Items 4 through 6 were caused by differential settlement of the perimeter foundation along the west face of the structure. This type of settlement was not the result of the recent structural modifications in the condo below. In general, differential settlement occurs when soil under a footing compresses. The cause of soil compression could be either a) moistening of the subgrade soil by water infiltration, b) drying of clay-like soils, c) crumbling of decomposing organics in a subterranean layer, d) inadequate compaction of the soil prior to construction of the foundation, e) additional loading applied to an existing foundation through structural additions, expansions, or modifications, or f) hillside slope creep due to an adjacent slope slowly shifting.
a) Inadequate drainage of surface water away from the home often contributes to subgrade soil saturation. Inadequate drainage occurs when the topography is flat, topography slopes toward the house, irrigation volume is unnecessarily high, torrential rains create ponding conditions, water has no escape route (bathtub scenario), or drains are blocked. The adjacent yards/planter areas are flat or drains towards the house. For this particular house, water may have saturated the soil adjacent to this foundation due to inadequate surface drainage during irrigation, past torrential rains, or an interior water leak. Proper drainage is important to keep water away from perimeter foundations to prevent foundation movement. Water percolates through the top soil to saturate the subgrade soil under the foundation. In such conditions, the soil under the foundation becomes more compressible. This is most likely a contributing cause of the settlement observed at this house.
b) Clayey soils have a high expansion rate. Upon dying, these soils shrink which leads to differential settlement. Upon moistening, these soils expand. In either case, differential settlement will occur. This is most likely a contributing cause of the settlement observed at this house. See the section below for more information.
c) If organic material (roots, fossils, etc.) decomposes, the surrounding soil will collapse into the previous volume. It is difficult to ascertain the probability that this has occurred although the condo owner describe root damage in the past under the house.
d) If the soil was not compacted properly prior to construction of the original footings, short term (2 weeks) and long term (5 years) settlement is expected when the load of the house is applied to the soil. It is not possible to assess compaction under the house, once the house is constructed above.
e) The house does not appear to have had structural additions, expansions, or modifications at the perimeter in the regions along the west side where the settlement must have occurred.
f) A hillside condition does occur at this property approximately 20ft to the west of the west face of the structure. Slope creep may have been a contributing cause to the differential settlement. See the section below for more information.