Lumber comes from trees and most building lumber comes from pine trees.
In the pine tree species there are 14 types of soft woods (pine trees).
In each soft wood there are at least 5 classifications of strengths of each type of wood:
* Select structural clear wood
* No.1 with small knots
* No.2 with knots 3/4″ and smaller
* No.3 with knots 2″ and smaller
* No.4 with large knots
When the trees are cut into boards at the mill, they spray paint on the ends of the studs. The darker the color of paint, the better quality lumber you are building with.
Color ratings are purple, red, orange, light blue, and light green.
The darker the color, the better the lumber. Better lumber holds nails better, and the wood will not bow, twice, cup, or check as much as the lighter colors.
A lot of information but what does it mean?
What if your house is designed for Douglas fir floor joists and your contractor wants to save money and installs balsam or spruce floor joists instead?
The contractor changed your floor load rating from 17.6 lbs. dead load (furniture) and 60 lbs. live load (people) to 17 lbs. dead load, and 33 lbs live load — now your floor is not even legal.
I’ve seen it happen a lot.
Similarly, poor quality studs do a number on sheetrock — install it, and you can count all the screw and nail pops over time.