MHIC Construction Methods and Materials 3 — Questions and Answers
Question 1: A contractor is installing a load-bearing wall on the first floor of a two-story home. Which type of lumber grade is most appropriate for the structural studs in this wall?
- Select Structural or No. 1 grade (Correct answer)
- No. 3 grade or Construction grade
- Utility grade
- Appearance grade (C Select)
Correct answer: Select Structural or No. 1 grade
Load-bearing walls require lumber with high strength and minimal defects. Select Structural or No. 1 grade lumber meets the strength requirements for structural applications. Lower grades like No. 3 or Utility have more knots and defects that reduce load capacity and are not suitable for primary structural members.
Question 2: When framing a floor system, a contractor uses engineered I-joists instead of solid sawn lumber. What is the PRIMARY advantage of I-joists over traditional dimensional lumber for long spans?
- They are less expensive to purchase
- They provide a higher strength-to-weight ratio and resist warping and shrinkage (Correct answer)
- They are easier to cut with standard hand tools
- They eliminate the need for blocking between joists
Correct answer: They provide a higher strength-to-weight ratio and resist warping and shrinkage
Engineered I-joists are manufactured from oriented strand board (OSB) webs and laminated veneer lumber (LVL) flanges, giving them a high strength-to-weight ratio. They are dimensionally stable, resisting warping, twisting, and shrinkage that causes squeaky floors. This makes them ideal for long spans where solid lumber would require larger, heavier members.
Question 3: A homeowner's bathroom renovation requires waterproofing behind the tile in a shower surround. Which substrate is most appropriate directly behind ceramic tile in a wet shower area?
- Standard drywall (gypsum board)
- Cement board (cementitious backer unit) (Correct answer)
- OSB (oriented strand board)
- Greenboard (moisture-resistant drywall)
Correct answer: Cement board (cementitious backer unit)
Cement board (cementitious backer unit) is the correct substrate for wet areas like shower surrounds because it does not absorb water, will not rot, swell, or degrade when exposed to moisture. Standard drywall and OSB will fail when wet. Greenboard is only moisture-resistant, not waterproof, and is not suitable for direct water exposure in shower applications.
Question 4: During a concrete pour for a residential foundation wall, what is the purpose of 'screeding' the concrete?
- Adding reinforcing steel rebar to the mix
- Leveling and striking off excess concrete to achieve a flat, even surface (Correct answer)
- Applying a curing compound to prevent rapid moisture loss
- Vibrating the concrete to remove air pockets
Correct answer: Leveling and striking off excess concrete to achieve a flat, even surface
Screeding is the process of striking off excess concrete and leveling it to the desired elevation using a screed board or rod drawn across the tops of forms. It creates a flat, even surface and is typically one of the first finishing steps after concrete is placed. Vibrating removes air pockets (consolidation), curing compounds prevent moisture loss, and rebar is placed before the pour.
Question 5: A contractor is installing a new roof on a home in a climate with frequent freeze-thaw cycles. In addition to felt underlayment, which additional material is required by most building codes at the roof's eaves?
- Roofing cement applied in a continuous bead
- Ice and water shield (self-adhering membrane) (Correct answer)
- A second layer of 30-lb felt underlayment
- Metal drip edge installed over the felt
Correct answer: Ice and water shield (self-adhering membrane)
Ice and water shield is a self-adhering, waterproof membrane required by most codes in cold climates at eave overhangs and valleys. It protects against ice dam damage, where backed-up meltwater can penetrate beneath shingles. It is installed directly on the roof deck before felt underlayment. While drip edge is also required, it does not provide ice dam protection.
Question 6: When installing a wood-framed exterior wall, horizontal blocking installed between studs mid-height serves which PRIMARY code-required purpose?
- To provide a nailing surface for exterior sheathing seams
- To act as a fireblock, slowing vertical fire spread through the wall cavity (Correct answer)
- To add lateral bracing against wind loads
- To support the weight of the wall sheathing panels
Correct answer: To act as a fireblock, slowing vertical fire spread through the wall cavity
Building codes require fireblocking in concealed wall cavities to slow the spread of fire and smoke through concealed spaces. In stud walls over 10 feet tall, horizontal blocking is installed at mid-height to interrupt the vertical air channel within the stud bay. While blocking can also serve as a nailing surface, the primary code-mandated purpose is fire resistance and containment.
MHIC Construction Methods and Materials 3
A contractor is installing a load-bearing wall on the first floor of a two-story home.
Which type of lumber grade is most appropriate for the structural studs in this wall?