A 2x4 is really 3-1/2" thick — so why does the blueprint dimension the wall at 4"? Learn how architects dimension plans, how to transfer those dimensions to your framing layout from the outside of the brick, and why that missing half-inch compounds into real errors by the last wall.
Architects dimension interior partitions at a nominal 4". The stud you frame with is 3-1/2" — know which number you're holding before you pull tape.
The plan shows 11": 2x6 stud (5-1/2") + 1/2" OSB + ~4-1/2" brick assembly ≈ 10-1/2", rounded to 11" on the drawing. It varies plan to plan — verify every time.
Hook your tape on the outside of the brick. Add the interior dimension plus the shown wall thickness: 11" + 15' + 4" = 16'3" to the outside of the interior wall.
A 4" interior wall on paper is a 3-1/2" stud wall on the deck. An 11" exterior wall is stud + sheathing + brick. Match every dimension to its real assembly before you pull tape.
Start every layout from the exterior face of the brick, then add the plan's room dimension plus the wall thickness shown — e.g. 11" + 15' + 4" lands you at 16'3".
The plan's 4" wall frames at 3-1/2". A closet drawn at 5'10" plus a 4" wall reads 6'2" on paper — but you'll frame 5'10-1/2" of clear space between studs.
Half-inch misses compound across a house. Understand the architect's dimensioning on day one — don't guess, read the plan, build it right.
Every wall framed at 3-1/2" against a plan dimensioned at 4" hides a 1/2" miss. See how far off you land across the whole house.