Wood flooring grades: what the names mean and how to specify one

At a glance

Letters are the sources listed under "The same name, different limits". Millimetres are the largest knot the source allows. Percentages are of the visible board face. Figures are what each source printed, not a standard.

The same name, different limits

A grade is a supplier's own appearance category for floor boards: how many knots, how much sapwood, how much colour variation, and whether filler is used. In the UK these categories are not set by any standard we could read. One flooring maker says it uses its own definitions because timber comes from many countries with different grading rules, and a retailer says grading standards are not universally regulated. The result is that Prime, Select, Natural and Rustic are labels, not measurements.

We read eight published UK definitions (listed below; the dated ones run from 2012 to 2023). Only three print any limits at all, and where they do the figures do not agree. A Select board has no knots in one source, knots up to 5 mm in another and up to 20 mm in a third. A Character board may be up to 30% sapwood in one source and 5% in another.

Sources are labelled A to H rather than named. Dates are the page or file dates we could see; several pages are undated, so check the supplier's current wording before you rely on a figure.

The disagreements fall into four kinds:

• Rank. Two sources (A and E) put Select above Prime. Three (B, D and F) put it below.
• Size of knot. The largest knot allowed in a Select board runs from none to 20 mm, and in a Rustic board from 35 mm to no limit.
• Sapwood. The share of the board face allowed to be sapwood runs from none to 20% in Prime, 5% to 30% in Character and 20% to 40% in Rustic.
• Natural. It sits between Prime and Rustic in two sources and is another name for Rustic in a third. Letters travel a little better than names: B and G both put AB at the top and ABCD below ABC. But no source defines the letters against a standard.

What a written grade looks like

A grade can be written so that it is checkable. The one defined scheme we read is American: the NWFA/NOFMA rules for solid unfinished flooring, published by the National Wood Flooring Association. It is not a UK standard and it does not cover engineered or prefinished boards, but it shows what a written grade contains.

• Limits, not adjectives. Each oak grade lists what it admits and what it does not. For example, the No. 1 Common grade does not admit broken knots over 1/2 in (12.7 mm) across, and the Select grade admits one small tight knot in every 3 ft (914 mm) of board.
• A tolerance. The target is 100% on grade, with up to 5% of pieces allowed to be below grade.
• Appearance only. The rules say appearance alone decides the grade, because all grades are equally strong and serviceable.
• Other words defined too. A floor may only be sold as quarter-sawn if at least 50% of each piece shows quartered features, so even the cut has a written test.

The UK sources above do none of this: no tolerance, no stated test, and mostly no numbers. That is why the name alone should never be the specification.

What a grade does not tell you

A grade is a description of appearance on the day the boards are graded. It does not tell you the following, and each needs its own line in the specification.

• Strength or wear. The NWFA/NOFMA rules say all grades are equally strong and serviceable, and a UK retailer says the grade has nothing to do with the quality of the wood. A cheaper grade wears the same; it simply shows more of the tree.
• Colour after finishing. One maker notes colour variation stays modest unless a reactive finish such as smoking or fuming is used, which exaggerates it. Approve the sample in the finish, not in the raw timber.
• The cut. Flat-sawn, quarter-sawn and rift-sawn boards look different within the same grade. State the cut separately.
• Board size. A maker of very wide planks says sapwood streaks, knots and medullary rays should be expected in most planks of that size, because each board shows more of the tree. Wide boards need a looser reading of any grade.
• Filler. Where filler is allowed its colour is meant to complement the wood, and one maker says it may vary from batch to batch. Say which defects may be filled and match the filler to the sample.

Making a grade enforceable

Because the name does not carry the meaning, the specification has to. This is the order that works, and none of it relies on a UK standard.

1. Name the written rules. Ask the supplier for its grading rules in writing and quote them, with their date, in the specification. Do not accept a name on its own.
2. Approve a physical range panel. A board or panel chosen to show the lightest and darkest boards, the fewest and most knots, the most sapwood and any filled knots the grade admits. Sign it, date it and photograph it in the light the room will have. On a floor we coordinate, we take the partner workshop's written grading rules and agree the range panel with you once the scope is settled.
3. Say what is allowed outside it. Give a percentage of boards that may fall outside the range, and say what happens to them: set aside before fixing and replaced. The one scheme we read allows up to 5% of pieces below grade. Treat that as a starting point for discussion, not a UK norm.
4. Fix the inspection point. Inspect on delivery, before any board is fixed. Some makers' terms treat fixed boards as accepted, and our installation guide says to judge a floor from a normal standing or seated position, in the light the room will have, counting only what is immediately obvious.
5. Mix the packs. UK installation guidance says boards should be taken from three separate packs, not all from one, so that colour and knots spread evenly.

The wording below turns the list into paste-in text. Our wood flooring installation guide covers what happens next on site.

Standards nearby, and what we could not read

Two families of standard sit nearby, and we could read neither.

• Product standards for parquet. BS EN 13226 covers solid parquet elements with grooves or tongues, and BS EN 13489 covers multi-layer parquet elements. The contents lists we saw show appearance clauses, including a "free class" for which the principles are in an annex. We could not read the text, and the listings disagree about which edition is current, so ask the maker whether the product is supplied to one of them and under which appearance class.
• Timber in joinery. BS EN 942 classifies timber by appearance for joinery (its J classes), and one supplier's example specification cites it for a flooring appearance class. We have not read it and do not know whether it is meant for floor boards.

Neither replaces a signed sample. They are worth asking about because a maker who supplies to a standard can give you a declaration of performance and a named appearance class to quote alongside the sample.

Grade: as the approved range panel ref [FL-GR-01], [oak], [pre-finished / finished on site] in [finish ref], signed by [designer], [main contractor] and [flooring contractor] on [date] and held at [location]. Names such as Prime, Select, Natural or Rustic do not define the grade on their own. Not more than [x]% of boards, by [area / number], may fall outside the range shown. Boards outside the range are to be set aside before fixing and replaced at no cost to the project.

Grade: [supplier]'s written grading rules ref [ ] dated [date], issued with the tender. In the absence of a stated limit the following apply: knots [sound only / sound or filled], not larger than [20] mm across; sapwood not more than [10]% of the visible face of any board; checks [none / hairline and sound]; colour variation within the range of approved sample [FL-GR-01]; filler [permitted in listed defects only], colour matched to the sample. Board length and width as [schedule ref].

Boards to be inspected on delivery and before any board is fixed, by [flooring contractor] with [designer / contractor], from a normal standing position in the lighting to be used in the room, against the approved sample. Boards are laid from not fewer than [three] packs at a time. Boards fixed in place are accepted only if they were inspected under this clause. Record of inspection to be issued to [designer] within [two] working days.

Standards and sources

• No standard we could read fixes the names Prime, Select, Natural or Rustic: eight UK supplier definitions were read, A to H; none cites a standard for its grades.
• NWFA/NOFMA International Standards for Unfinished Solid Wood Flooring: National Wood Flooring Association (US). Read in full. Solid unfinished flooring only; the cover is marked revised April 2009 and the pages April 2018. Used here only to show what a written grade looks like.
• BS EN 13226 and BS EN 13489: solid and multi-layer parquet product standards, with appearance clauses. Named; text not read; edition status to confirm.
• BS EN 14342:2013: wood flooring and parquet: characteristics, conformity and marking. Named; not read.
• BS EN 942:2007: timber in joinery, general requirements (J classes). Cited by one supplier's example specification; not read.

Questions we are asked

Is there a British Standard for wood flooring grades?

Not one that fixes the names Prime, Select, Natural or Rustic, as far as we could find. The European product standards for solid and multi-layer parquet (BS EN 13226 and BS EN 13489) include appearance rules, which we could not read, and a supplier's own grade may sit beside them. The practical answer is a signed sample board and a stated percentage allowed outside it.

Is Select better than Prime?

It depends on who wrote the grade. Of the five UK sources that list both, two put Select above Prime and three put it below. Compare the written limits or, better, the approved sample, and ignore the order of the names.

What do AB, ABC and ABCD grade mean?

In the sources that use them, AB sits at the top and CD at the bottom, and a mixed grade such as ABCD allows more sapwood, knots and colour variation than AB. But no source we read defines the letters against a standard, so ask for the limits in millimetres and per cent of the face, or for a sample.

What is natural grade oak flooring?

Usually the middle of a supplier's range: more knots and colour variation than Prime, fewer than Rustic. One UK maker uses natural as another name for Rustic, and the one source that gives a number allows knots up to 30 mm. Treat the word as a label and ask for the limits.

Does the grade affect how long the floor lasts?

No. The NWFA/NOFMA rules say all grades are equally strong and serviceable, and a UK retailer says the grade has nothing to do with the quality of the wood. Grade changes how the floor looks: how many knots, how much sapwood and how much colour variation. Durability depends on the species, the construction and the finish.

How do I check the grade when the boards arrive?

Compare them with the signed sample before any board is fixed, in the light the room will have. Count the share of boards outside the range and measure it against the percentage in your specification. Some makers' terms treat boards as accepted once they are fixed, so inspect first.