Construction Methods and Materials 2 Flashcards

A contractor is installing a load-bearing wall in a residential addition. Which type of lumber is specifically graded and approved for structural applications?

Answer: Select structural lumber

Select structural lumber carries the highest structural grading designation and is engineered and tested for load-bearing applications. Construction-grade lumber is general purpose but not optimized for structural loads, appearance-grade prioritizes aesthetics, and furring strips are non-structural thin boards used for leveling surfaces.

When constructing a concrete slab on grade, what is the PRIMARY purpose of placing a vapor barrier (polyethylene sheeting) beneath the slab?

Answer: To prevent ground moisture from migrating up through the concrete

A vapor barrier beneath a concrete slab-on-grade is installed to block capillary moisture migration from the soil up into the concrete and finished flooring above. Without it, moisture can cause efflorescence, deteriorate flooring adhesives, and promote mold growth. It does not address frost heave, thermal insulation, or bonding.

In masonry construction, what does the term 'wythe' refer to?

Answer: A single vertical layer of masonry units one unit thick

A wythe is a continuous vertical section of masonry one unit in thickness. A double-wythe wall has two parallel layers of masonry. Mortar joints are called beds (horizontal) or head joints (vertical), metal connectors are called wall ties or anchors, and the top decorative course is called a coping.

A homeowner requests that OSB (Oriented Strand Board) be used for wall sheathing on an exterior renovation. Compared to plywood, which characteristic of OSB must the contractor account for during installation?

Answer: OSB is more susceptible to edge swelling when exposed to moisture

OSB's edges are more vulnerable to moisture absorption than plywood because the edges expose the strand layers directly, causing them to swell. This is why OSB requires proper sealing of cut edges and adequate drainage gaps. OSB and plywood have comparable racking resistance, similar fastener schedules, and both are code-approved for wind bracing.

When installing floor joists using the 'platform framing' method, where is the next story's wall framing erected?

Answer: On top of the subfloor deck that covers the floor joists

In platform framing (the dominant modern residential method), each floor level serves as a 'platform' on which the next story's walls are built. The subfloor sheathing is installed across the joists first, creating a flat working surface, then the walls are framed on top of that deck. This is distinct from balloon framing where studs run continuously from foundation to roof.

A contractor is selecting insulation for an exterior wall cavity in a climate with significant humidity. Which insulation type is most resistant to moisture absorption and will not lose R-value when wet?

Answer: Closed-cell spray polyurethane foam (SPF)

Closed-cell spray polyurethane foam has a very low moisture vapor permeability and does not absorb liquid water, maintaining its R-value even in humid conditions. It also acts as an air barrier. Fiberglass batts lose insulating effectiveness when wet, cellulose is hygroscopic and can hold moisture, and mineral wool is more moisture-resistant than fiberglass but still less effective than closed-cell SPF in high-humidity applications.