403A Floor, Wall & Roof Framing

Question 1

According to the National Building Code of Canada, what is the maximum allowable span for 38×184 mm (2×8) spruce-pine-fir floor joists at 400 mm O.C. spacing in a residential application?

Accepted Answer

Approximately 3.6 m

Answer

NBC span tables for 38×184 SPF joists at 400 mm O.C. for residential floor loads (1.9 kPa live load + dead load) yield approximately 3.6 m. Always consult current NBC tables as values depend on load, species, and grade.

Question 2

What is the purpose of blocking installed between floor joists at the bearing wall?

Accepted Answer

To prevent joist rotation and transfer loads to the bearing wall

Answer

Blocking (or solid bridging) at bearing walls prevents joist rotation under load, transfers vertical loads to the bearing wall, and helps distribute point loads. It also acts as a fire stop in some assemblies.

Question 3

When framing a load-bearing wall, what is the minimum number of jack studs (trimmer studs) required on each side of a door opening wider than 1 800 mm?

Accepted Answer

Two jack studs on each side

Answer

For openings wider than 1800 mm, the NBC and standard practice require two jack studs on each side to adequately support the increased header load. Narrower openings typically use one jack stud per side.

Question 4

What is the purpose of a let-in brace in wood frame wall construction?

Accepted Answer

To provide racking resistance (lateral load resistance) in the wall

Answer

A let-in brace is a piece of 19×89 mm (1×4) lumber notched into studs at a 45° angle from top corner to bottom corner. It resists racking forces (lateral loads from wind and seismic) that would otherwise push the wall out of plumb.

Question 5

What does 'crown up' mean when installing floor joists?

Accepted Answer

Install the joist with the natural bow facing upward so floor loads will straighten it

Answer

Lumber often has a slight natural bow or crown along its length. Installing joists crown up means the convex side faces up. Floor loads compress the crown down toward straight, preventing a visible hump. A crown installed downward will sag further.

Red Seal Carpenter 403A Practice Test

Red Seal Carpenter 403A Practice Test

403A Floor, Wall & Roof Framing