Wallace Design Collective

There are several issues that arise when modifying existing structures that differentiates these types of projects from ground-up design and construction. One such issue is the extent of condition assessment of the existing structure that is to be performed by the design team. Whether it be an acquisition and conversion of an existing structure to a different use or a larger expansion of an existing structure, our experience has found that it is important to communicate with the client and owner the level of structural condition assessment that is to be provided and the associated levels of risk that come into play based on the extent of the assessment.

Depending on the age, condition, load capacity and proposed modifications to an existing structure, among other things, a site specific approach to the project should be developed and discussed with the building owner.  For example, an older structure with no existing drawings might justify additional assessment efforts than a newer structure where existing design documents are available.  Also, older buildings are more likely to have experienced structural deterioration over time due to exposure to the elements if maintenance items such as roofing, painting, and waterproofing have not been properly implemented over the life of the structure. If substantial modifications are proposed for a project that will impact the load bearing structure or lateral system, or trigger a code required retrofit, a more in-depth structural assessment of the existing structure may be warranted versus a limited remodel that may have minimal impact on the structural system.

Our experience has been that the more effort spent initially assessing the existing structure will lead to reduced unforeseen conditions and resulting change orders discovered during construction.  There are limitations that come into play in the assessment of the existing structure such as hard finishes in place, previous occupant build outs, etc. that limit access. It is important to make known these limitations with the client and owner when reporting the assessment findings.  If finishes or obstructions are in place, it may be worth considering some isolated areas of finish material demolition to allow access to the structure for assessment. This might include areas of roofing removal, interior ceiling removal, non-structural wall removal, slab covering removal, etc.  In some cases, material sampling and testing or Geotechnical exploration may be warranted depending on the scope of work of a given project and the extent of original construction documents that are available.

Regardless of what level of condition assessment is decided to be appropriate for a given existing structure, it is important to have a documented conversation with the owner in order to establish a clear understanding by all parties as to what level of assessment is to be performed and the associated level of risk for the owner that will result during construction.