Lecture Notes

Size Categories and Commercial Grades

Size Categories

category nominal
thickness
(in.) nominal
width
(in.)

boards 0.75-1.5 ≥2

dimension lumber 2-4 ≥2

timbers ≥5 ≥5

Size Subdivisions & Commercial Grades

different design values based on size categories, which are based on anticipated use, but actual use can vary

size
category size
subdivision nominal
thickness (in.) nominal
width (in.) commercial
grades NDS
supplement

boards stress-rated board (SRB) 0.75-1.5 ≥2 -- --

dimension
lumber light framing (LF) 2-4 2-4 construction
standard
utility tables
4A, 4B,
4C, 4F

structural light
framing (SLF) select structural
no. 1 and better
no. 1
no. 2
no. 3

structural joists
and planks (SJ&P) ≥5

stud ≥2 stud

decking ≥4 select decking
commercial decking table 4E

timbers beams and
stringers (B&S) ≥5 more than 2
greater than
thickness dense select structural
select structural
dense no. 1
no. 1
dense no. 2
no. 2 table 4D

posts and
timbers (P&T) not more than 2
greater than
thickness

category	nominal thickness (in.)	nominal width (in.)
boards	0.75-1.5	≥2
dimension lumber	2-4	≥2
timbers	≥5	≥5

size category	size subdivision	nominal thickness (in.)	nominal width (in.)	commercial grades	NDS supplement
boards	stress-rated board (SRB)	0.75-1.5	≥2	--	--
dimension lumber	light framing (LF)	2-4	2-4	construction standard utility	tables 4A, 4B, 4C, 4F
	structural light framing (SLF)		2-4	select structural no. 1 and better no. 1 no. 2 no. 3
	structural joists and planks (SJ&P)		≥5	select structural no. 1 and better no. 1 no. 2 no. 3
	stud		≥2	stud
	decking		≥4	select decking commercial decking	table 4E
timbers	beams and stringers (B&S)	≥5	more than 2 greater than thickness	dense select structural select structural dense no. 1 no. 1 dense no. 2 no. 2	table 4D
timbers	posts and timbers (P&T)	≥5	not more than 2 greater than thickness		table 4D