Wood: NASCLA Commercial General Building Practice Questions
Lumber sizes and grades, framing members, engineered wood, trusses and their bracing, sheathing and fasteners, decay and fire-retardant treatment, and board-foot takeoffs.
Question 1
What are the actual dressed dimensions of a nominal 2x10?
Correct answer: 1-1/2 x 9-1/4 inches
Trade practice (lumber sizes)
Dimension lumber 8 inches and wider loses 3/4 inch in width when dressed (2x10 = 9-1/4 in); narrower pieces lose 1/2 inch (2x6 = 5-1/2 in).
Question 2
Calculation
How many board feet are in one 2x6 that is 12 ft long?
Correct answer: 12 board feet
Estimating math (board feet)
A board foot is 1 in × 12 in × 1 ft (144 cubic inches). Board feet use nominal dimensions. Forgetting to divide by 12 gives 144.
An order is 80 pieces of 2x10 joists, each 16 ft long. How many board feet is that?
Correct answer: 2,133.33 BF
Estimating math (board feet)
Find board feet per piece, then multiply by the count (or do 2 × 10 × 16 × 80 ÷ 12 in one step).
Worked solution
1
Formula
One piece = 2 × 10 × 16 ÷ 12 = 26.67 BF
2
Values
Total = 26.67 × 80
3
Result
Total = 2,133.33 BF
Question 4
Calculation
Lumber is priced at $850 per thousand board feet (MBF). What is the cost of 2,400 board feet?
Correct answer: $2,040.00
Estimating math (board feet)
M means 1,000. Divide the board feet by 1,000, then multiply by the price per MBF.
Worked solution
1
Formula
Thousands of board feet = 2,400 ÷ 1,000 = 2.4 MBF
2
Values
Cost = 2.4 × $850
3
Result
Cost = $2,040.00
Question 5
Calculation
A wall is 48 ft long with studs at 16 inches on center. Counting one stud per space plus one to finish the end (and no extras for corners or openings), how many studs are needed?
Correct answer: 37 studs
Estimating math (framing)
Divide the length by the spacing and add one for the end. Real takeoffs then add studs at corners, intersections and openings.
Worked solution
1
Formula
Wall length = 48 ft × 12 = 576 in
2
Values
Spaces = 576 in ÷ 16 in = 36
3
Result
Studs = 36 + 1 = 37 studs
Question 6
Lumber stamped "S-DRY" or "KD19" has a maximum moisture content of what?
Correct answer: 19 percent
Trade practice (lumber grades)
Surfaced-dry lumber is dried to 19 percent or less before planing; S-GRN (green) is above that. MC15 or KD15 means 15 percent.
Question 7
What information does a lumber grade stamp give?
Correct answer: Grading agency, mill, species, grade and moisture condition
Trade practice (lumber grades)
The stamp identifies the certified grader and the properties the designer relied on; inspectors check it on structural lumber.
Question 8
Which engineered wood product is made of thin veneers glued with the grain all running lengthwise, and is often used for headers and beams?
Correct answer: Laminated veneer lumber (LVL)
Trade practice (engineered wood)
LVL lays all veneers parallel for strength along its length; plywood alternates the grain direction of its layers, and OSB is made of oriented strands.
Question 9
What is glued-laminated timber (glulam)?
Correct answer: Lumber laminations glued into large structural members
Trade practice (engineered wood)
Glulam beams and arches are built up from layers of lumber, allowing large sizes, curves and high strength.
Question 10
A plumber wants to cut through the flange of a wood I-joist to pass a pipe. What is the correct response?
Correct answer: Never cut flanges; use only web holes the maker allows
Trade practice (I-joists)
The flanges carry the bending forces; manufacturers publish hole charts for the web only, and any other cut needs an engineered repair.
Question 11
Under truss industry guidance (BCSI), what is a key rule for handling and installing metal-plate-connected wood trusses?
Correct answer: Brace trusses as they are set, per the truss drawings and BCSI
Trade practice (BCSI trusses)
Unbraced trusses can domino over; temporary and permanent bracing, careful lifting and no field cutting without the truss designer's approval are core BCSI practices.
Question 12
A truss chord is damaged during delivery. What should the contractor do?
Correct answer: Get a repair detail from the truss designer before installing it
Trade practice (BCSI trusses)
Trusses are engineered as a system; damaged members need an engineered repair or replacement.
Question 13
A plywood or OSB panel is stamped with a span rating of "32/16". What does it mean?
Correct answer: 32-inch roof span and 16-inch floor span
Trade practice (sheathing)
The left number is the maximum roof span and the right number the maximum floor span, in inches, with the long dimension across the supports.
Question 14
Why are wood structural panels installed with a small gap (about 1/8 inch) at edges and ends?
Correct answer: To let panels expand without buckling
Trade practice (sheathing)
Panels grow when wet; without spacing they push against each other and ridge or buckle.
Question 15
Wood framing members that rest on concrete in direct contact with the ground generally need what protection under the IBC?
Correct answer: Treated or naturally durable wood
IBC 2021 2304.12
Sills and sleepers on concrete in contact with the ground wick moisture and decay unless they are treated or naturally durable.
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Practice questions are written in our own words and cite code sections by number. Always study from your own copy of the code and the official candidate bulletin.