National Home Inspector Exam (NHIE) Structure and Foundation Summary

Concrete shrinks as it cures, so hairline vertical cracks are very common in poured walls. If there is no offset (one side shifted), no widening, and no water, it is usually not structural. Inspectors still report it and may suggest sealing and monitoring.

Wrong choices

• Major foundation failure: A hairline crack with no offset or movement is not a sign of major failure.
• Termites eating the concrete: Termites do not eat concrete.
• A leaking roof: Roof leaks do not crack foundation walls.

Soil outside a basement wall pushes inward, more so when it is wet or frozen. Block walls are weak against this sideways pressure, so they crack along a mortar joint near mid-height and bow inward. This is a serious structural concern.

Wrong choices

• Normal concrete shrinkage: Shrinkage cracks are usually vertical and do not cause bowing.
• Too much attic ventilation: Attic ventilation has no effect on the foundation.
• A leaking roof: A roof leak does not push a basement wall inward.

Masonry cracks along the weakest path, which is the mortar joints. When one part of a foundation settles more than another (differential settlement), the crack steps up or down diagonally. Width and offset help show how serious it is.

Wrong choices

• Normal shrinkage of new mortar: Shrinkage cracks are fine and scattered, not a clear stair-step pattern.
• Mortar that was just applied: Fresh mortar does not form stair-step cracks.
• A lightning strike: Lightning is not the usual cause of stair-step cracks.

When water soaks through concrete or masonry, it carries dissolved salts. The water dries at the surface and leaves white crystals behind. Efflorescence itself is harmless, but it shows that moisture is passing through the wall.

Wrong choices

• The wall is covered with mold: Efflorescence is mineral salt, not mold, though both can mean moisture.
• The wall is about to collapse: Efflorescence alone does not mean structural failure.
• The concrete was recently painted: Paint does not create efflorescence.

Subterranean termites live in the soil and need moisture. They build mud tubes up foundation walls to reach wood while staying protected. Inspectors report mud tubes and recommend evaluation by a licensed pest control professional.

Wrong choices

• Carpenter ants: Carpenter ants leave sawdust-like debris (frass), not mud tubes.
• Powderpost beetles: Powderpost beetles leave small holes and fine powder.
• Rodents: Rodents leave droppings and gnaw marks, not mud tubes.

A truss is an engineered unit where every piece shares the load. Cutting or removing any chord or web can weaken the whole truss. Altered trusses should be reported, and repair should follow an engineer's design.

Wrong choices

• Metal gusset plates fully pressed into the wood: Fully seated plates are correct.
• Trusses spaced evenly: Even spacing is normal.
• Trusses bearing on the exterior walls: Trusses are designed to bear on the outside walls.

A horizontal crack with inward bowing shows the wall is losing its fight against soil pressure. This is a structural concern beyond the scope of a home inspection. The report should describe the crack and bowing and recommend evaluation by a qualified structural engineer.

Wrong choices

• Monitor it for a few years before doing anything: With visible bowing, waiting can let the wall get worse; evaluation is needed now.
• Patch the crack with caulk and repaint: Patching hides the crack but does not stop the soil pressure.
• No action; this is normal for block walls: Horizontal cracks with bowing are not normal.

Concrete wicks moisture from the ground. Wood placed directly on it stays damp. Common model codes require sill plates on concrete or masonry to be pressure-treated or a naturally durable species to prevent rot.

Wrong choices

• Untreated pine: Untreated lumber on concrete absorbs moisture and rots.
• Particleboard: Particleboard swells and falls apart when wet.
• Drywall: Drywall is not a structural material.

Anchor bolts are set in the concrete and pass up through the sill plate, where nuts and washers clamp it down. They keep the house from sliding or lifting off the foundation in wind or earthquakes.

Wrong choices

• Support floor joists in the middle of their span: Mid-span support comes from beams and posts.
• Ground the electrical system: Grounding uses electrodes such as ground rods.
• Drain water out of the wall: Anchor bolts have no drainage role.

Bare soil gives off a lot of water vapor. A plastic vapor retarder (commonly 6-mil polyethylene) laid over the soil keeps much of that moisture out of the crawlspace air, which helps prevent mold, rot, and rusting. Torn or missing sheeting is a common finding.

Wrong choices

• Insulate the floor above: Plastic sheeting has almost no insulating value.
• Stop termites completely: A vapor retarder is not a termite barrier.
• Support the piers: It carries no load.