NWFA and NOFMA Explained
The NWFA (National Wood Flooring Association) is the governing body and trade group of the wood flooring industry in the US. NOFMA (National Oak Flooring Manufacturers Association) used to be a separate organization until the two combined in 2008 and for the rest of this article we will be using NWFA as our denotation. It is important to know that participation in the NWFA standards is 100% voluntary, meaning there are mills and products that do not adhere to these standards. This body has been recognized by our federal government and the standards set out are widely followed. These regulations are only set for domestic American hardwood products.
Unfinished Solid Hardwood
The first set of grading standards set forth by the NWFA are for unfinished domestic hardwoods such as: Oak, Maple, Birch, Hickory, Ash, Walnut and Cherry.
Grading is based on the face or top part of the wood. This is because all grades carry the same structural soundness. Grades are based solely on visual imperfections commonly referred to as "character." This can mean checking (small along-the-grain cracks), burls, knots, wormholes and mineral streaking. Grades are laid out below:
Clear - Uniform in color, mostly heartwood or sap wood. (Here for the difference) No visible checking, knots, worm holes, burls or mineral streaks. Incredibly clean appearance.
Select - The least amount of color variation between the boards, and between sapwood and heartwood. This is the cleanest grade available with the most consistent coloring and grain pattern. If this grade has knots they will be the size of a pencil eraser or smaller.
#1 Common - More prominent color variation. Contrasting mix of heart and sapwood, variations from mineral streaking and manufacturing processes. Natural character is prominent and allowed in greater size. Knots will be up to 1" to 1 1/2" in diameter, but they will not be open knots (meaning you can't hold the board up and see through the board).
2 Common - Plenty of color variation, highly contrasting appearance. Knots up to 2" to 2 1/2" in diameter. Open knots, busted tongues, broken ends. This is typically the cheapest option with the most waste. It is serviceable but plan ahead! Please plan on 12-15% waste factor if pursuing a #2 common project.
Combination Grades
You tend to see a mix of grades listed as:
Select and Better - A mix of select and clear grade, nothing in this mix is less than select.
No. 1 and Better - A mix of No.1 Select and possibly clear grades. Nothing in this mix is less than No. 1.
No. 2 and better - A mix of No. 2 and better grades. Not likely to see much select and better but a healthy mix of #1 and #2 to be expected.
Mill Run / Character - Colloquial terms that we use to describe a No. 2 and better combination grades. These products contain a mix of all the grades. There is typically more waste but at a great price.
Moisture Regulations
Fear not, there are standards for that too!
NWFA regulations state that no more than 5% of unfinished planks may be outside of a 6-9% moisture range at point of manufacture, and at time of shipping.
When you receive solid hardwood flooring you want to acclimate it to your homes moisture content see here for an article on that.
Video Explanations