“Good Bones” of a Structure (Engineering Perspective)

A fairly frequent question for a prospective homeowner, or an advising agent, is about the “bones” of a home.  When someone talks about the “bones” of a house, they are usually focused on primary components of the house (and likely not the cosmetic finish choices).   Think of it as a good home that has the potential to be great.  So this article is intended to give you an understanding of what “bones” are to an engineer, and how it is comprised of several components (and at times a little more difficult of a question to answer).

• Foundation (Foot Bone)

• Wall Elements (Femur)

When talking about the “bones” of a building, the wall elements are the femur (largest bone in the body, and are essential for standing).  The walls are the load resisting system of the building. These transfer the load from the roof system, ceiling and any additional floors to the foundation element. In states like Florida they also resist lateral wind forces, and in California provide diaphragm shear resistance.  To ensure your “bones” are good here, you have to consider the materials you are dealing with for the component.  The building somewhat talks to you, so you have to look for building distress.

Cementitious stucco lacks the capacity to flex when installed on concrete masonry unit (CMU) block, while wood framing with stucco tends to be more difficult to diagnose.  So cracked stucco following the block patter, a typical observation, can be an indication of shifting.  Small hairline (1/32-inch and less) are very common and are typically not indicative of a sizable issue, but large width cracks and those that demonstrate lateral offset between the cracked sections can be more concerning.  Again, if concerned you should hire an inspector or engineer with experience working with structural settlement.  For these experts, timeframe comes into play as well.  A small width crack that is highly aged is much less significant than a recently formed crack, that may be progressively worsening.  So look for evidence of age to the fractured surface, evidence of paint/patching material within the cracking, or other evidence to help find out the timeframe of occurrences.  This is certainly an area where you would go back to the sellers to inquire about the timeframe of painting/patching or distress development.  In wood-framed buildings, you look for racking of doors or windows, as cracking patterns in something like stucco may be misleading (especially once water starts infiltrating the cracks and may begin to rust metal lath).  If finished with a vinyl, wood or other type of siding, view of the wall movement is similarly obscured.  An irregular pattern cracking in a cementitious stucco here likely means shrinkage/thermal cracking and/or water intrusion.  Sometimes sounding on the stucco surface may help you determine if the assembly is sound.  Water damaged stucco over a wood substrate may give a more hollow sound when tapped.