Structural Systems
Structural Systems
The Structural domain tests how a house carries load and how it fails. Expect foundation types and defects, framing and connections, roof and ceiling structure, and evidence of movement, decay, or alteration. The inspector’s job is to identify observable conditions, explain the likely mechanism, and recommend further evaluation when the cause or remedy is beyond a visual inspection.
Core rules and concepts
- Load path: roof covering → sheathing → rafters or trusses → ceiling joists → exterior and interior walls → beams → columns → footings → soil. Look for interruptions: cut joists, removed walls, undersized beams, missing connectors, and posts that bear on soil or a thin slab.
- Foundation cracks: vertical hairline cracks in poured concrete are often shrinkage; diagonal cracks widening from a corner can indicate differential settlement; horizontal cracks in a block foundation with inward bowing suggest lateral soil pressure. A commonly used reporting threshold is 1/4 inch, but movement, offset, and pattern matter more than width alone.
- Framing cuts: for sawn lumber, a notch may not exceed one-sixth of the joist depth and may not be located in the middle third of the span; a bored hole may not exceed one-third of the depth and must be at least 2 inches from the top or bottom edge.
- Trusses: field cutting, removed webs, or added plywood gussets are defects unless supported by an engineer’s letter. Check gang plates and lateral bracing.
- Moisture and pests: probe sills, rim joists, and subfloor near grade; look for frass, mud tubes, and staining.
Worked example
A 2x10 floor joist measures 9.25 inches deep. The seller notched the bottom edge 2.5 inches deep at midspan to clear a drain pipe. One-sixth of 9.25 is about 1.54 inches, so the notch exceeds the allowed depth. Midspan is also in the middle third of the span, where notching is prohibited. Because the notch is on the tension edge, it reduces capacity significantly. Report the condition, note both violations, and recommend evaluation and repair by a licensed contractor or engineer.
Traps that cost marks
Treating every crack as structural failure; calling brick-veneer stair-step cracks foundation settlement without checking the veneer; missing altered trusses hidden by insulation; reporting a “failed” foundation without describing the observed mechanism; and inspecting only the visible basement wall while ignoring grading and downspouts.