InterNACHI Structural Systems & Components 3 — Questions and Answers
Question 1: What structural problem does 'sagging ridge line' most commonly indicate when observed from the exterior of a home?
- Improper shingle installation
- Undersized rafters, missing collar ties, or inadequate ridge beam support (Correct answer)
- Excessive attic insulation weight
- Normal settling in older homes
Correct answer: Undersized rafters, missing collar ties, or inadequate ridge beam support
A sagging ridge line typically indicates undersized rafters, missing or failed collar ties, inadequate ridge support, or rafter spread causing the ridge to deflect downward.
Question 2: What is the term for the condition where floor joists bear on a foundation wall or beam at less than the minimum required distance?
- Joist overhang
- Insufficient bearing (Correct answer)
- Undersized span
- Joist cantilever
Correct answer: Insufficient bearing
Insufficient bearing occurs when floor joists rest on a support surface with less than the code-required minimum contact length, typically 1.5 inches on wood and 3 inches on masonry.
Question 3: What does 'rafter spread' refer to in roof framing?
- The spacing between rafters
- The outward movement of exterior walls caused by rafter thrust (Correct answer)
- The length of rafter overhang beyond the wall
- The angle of rafter pitch
Correct answer: The outward movement of exterior walls caused by rafter thrust
Rafter spread is the outward horizontal force exerted by rafters on exterior walls, which can cause walls to bow outward if ceiling joists or collar ties don't resist this thrust.
Question 4: An inspector finds that a wood beam has a horizontal split running along its length. What type of defect is this?
- Compression failure
- Checking or splitting along the grain (seasoning crack) (Correct answer)
- Shear failure
- Tension failure
Correct answer: Checking or splitting along the grain (seasoning crack)
Horizontal splits running along the grain are called checks or seasoning cracks, caused by wood drying unevenly; while typically cosmetic, deep checks in load-bearing members warrant further evaluation.
Question 5: Which foundation type is most susceptible to damage from expansive (clay) soils?
- Deep pile foundations
- Shallow slab-on-grade foundations (Correct answer)
- Caisson foundations
- Drilled pier foundations
Correct answer: Shallow slab-on-grade foundations
Shallow slab-on-grade foundations are most vulnerable to expansive soils because clay soils swell when wet and shrink when dry, causing the slab to heave and crack.
Question 6: What is the structural function of a 'rim joist' (also called band joist or header joist)?
- To support the ridge board
- To cap the ends of floor joists and provide lateral support to the joist system (Correct answer)
- To carry point loads from posts above
- To anchor the floor to the foundation
Correct answer: To cap the ends of floor joists and provide lateral support to the joist system
The rim joist runs perpendicular to floor joists at the perimeter, caps joist ends to prevent rotation, and ties the floor system together laterally.
Question 7: During an inspection, a home inspector observes walls bowing inward in a basement. What is the most likely cause?
- Excessive interior humidity
- Lateral soil and hydrostatic pressure exceeding wall capacity (Correct answer)
- Improper wall insulation
- Thermal expansion of masonry
Correct answer: Lateral soil and hydrostatic pressure exceeding wall capacity
Basement walls bowing inward are most commonly caused by lateral earth pressure and hydrostatic pressure from saturated soils exceeding the wall's structural capacity.
InterNACHI Structural Systems & Components 3
What structural problem does 'sagging ridge line' most commonly indicate when observed from the exterior of a home?