Solid vs engineered wood flooring: construction and what changes

At a glance

Figures are those published in the sources named under "Standards and sources"; they are not product data. Heights and thicknesses are millimetres; 1 in = 25.4 mm.

What each build is made of

The word engineered describes how a board is built, not how good it is. A solid board is one piece of timber, the same species from face to back. An engineered board bonds a real hardwood wear layer to a core of other timber, so the layers can be arranged to restrain each other. The drawing shows the builds you will meet. Makers use the names two-layer, three-layer and multi-layer for different constructions, and no standard we read fixes them, so ask for a section drawing rather than relying on the label.

The core, and the notation

The core matters as much as the surface. Our guide to wood flooring over underfloor heating notes that a multi-layer plywood core is generally the most stable and that fibreboard cores are generally more sensitive to moisture, so ask which core a board has before asking about the face. Thickness is often quoted as total over wear layer: "14/3" is one UK retailer's notation for a 14 mm board with a 3 mm hardwood layer. Check what a given maker means, because the usable depth for sanding may be less than the layer quoted.

Movement: width and cut matter as well as construction

Wood changes size as its moisture content changes, and it changes most across the grain. The US Forest Products Laboratory's Wood Handbook (2021) says it shrinks and swells most along the growth rings (tangentially), about half as much across them (radially) and only slightly along the grain. For white oak the table gives 10.5% tangential and 5.6% radial shrinkage from green to oven-dry. Its equation 4-9 treats the change as linear below about 30% moisture content, so each percentage point of moisture content moves a flat-sawn oak board by about 0.35% of its width and a quarter-sawn one by about 0.19%.

That gives a worked answer to a question designers often ask. For a swing of 3 percentage points of moisture content, such as 12% in a damp summer to 9% in a heated winter, a free 190 mm flat-sawn oak board changes in width by about 2.0 mm. A 300 mm board changes by about 3.2 mm. A quarter-sawn board of the same width moves roughly half as much.

What the figures mean in a laid floor

Three things follow. First, movement is in proportion to width, so a board twice as wide moves twice as far: the NWFA's magazine makes the same point with an 8 in plank shrinking twice as much as a 4 in plank. Second, the cut changes the answer by about half. Third, these figures are for a board free to move. In a laid floor the adhesive and the neighbouring boards restrain it, so the same movement shows up as small gaps and, in a floor held tight, as pressure on the perimeter.

Engineered construction reduces this movement because the cross-laid layers pull against each other, but it does not remove it. The NWFA's magazine says engineered flooring is more dimensionally stable, yet still reacts to low humidity and can dry-cup, and in severe cases the wear layer can separate from the core. We found no published figure for how much a particular core cuts the movement, so ask the maker for test data, not a promise.

The chart uses US white oak, because that is the species in the Wood Handbook table, and the approximation in its equation 4-9. European oak is not in that table: ask the partner workshop for its species data. Shrinkage is a percentage of the green dimension, so real figures differ slightly.

Wear layers and refinishing

Refinishing is where the sources disagree most. Two published figures set the arithmetic. The NWFA's magazine says a traditional sand removes 1/32 to 1/16 in of timber (about 0.8 to 1.6 mm), and that sanding is not recommended where the wear layer is less than 3/32 in (2.4 mm). A UK retailer says each sanding takes roughly 1 mm and that a 3 mm wear layer can be sanded up to three times. Those two cannot both be right.

If we read the magazine's limit as the layer you have left before a pass, the number of passes a new wear layer allows is as follows. It is our arithmetic, from two published figures, not a maker's figure.

A pass is counted while at least 2.4 mm of the layer remains. Real sanding depth depends on the floor's flatness, the machine and the contractor.

On that reading a 3 mm layer allows a single light sand, where the retailer says three. A 4 mm layer allows two or three passes, and a 6 mm layer three to five. This fits the rule of thumb in our engineered vs solid guide that a deep wear layer is what keeps most of solid timber's life. A solid board has more to give: the magazine says solid floors typically have a wear layer of about 1/4 in (6.4 mm) or more and can be sanded six to eight times over a life. Whatever the construction, ask the maker for the usable depth above the tongue and groove and for its own count in writing.

Underfloor heating, wide boards and fixing

Underfloor heating dries the floor from below and cycles it daily, so it pushes every figure above to the edge. The NWFA's radiant-heat guidance names four levers: engineered construction, a species known for stability, quarter-sawn or rift-sawn cut, and narrow boards. Our own guide to wood flooring over underfloor heating treats engineered as the default and asks for any other choice to be approved in writing by the maker.

Width limits are the maker's statement, not an industry figure. One UK maker's installation guide says its multi-layer planks with a birch-plywood core can perform over underfloor heating at widths of 450 mm and above, and that the top layer will not be below 4 mm. That is one product's claim. For another product, or for a solid board, the answer may be a much narrower width or no.

Fixing follows from the build: bonded, floated or nailed, with different limits for each, and pattern floors are bonded. The conditions on site matter as much as the board, and they are set out in our acclimatisation and site conditions sheet and the installation guide.

What to write down

Species, pattern, finish and grade are chosen separately from the construction: herringbone can be solid or engineered, and an oiled finish suits either. What the specification has to carry is the construction itself.

Grade is a separate line: see our sheet on wood flooring grades. For pattern names and block sizes see the parquet pattern atlas.

Solid [European oak] flooring, [flat-sawn / quarter-sawn], [19] mm thick, [140] mm face width, [random lengths from 1.2 m], tongue and groove on all four edges, grade as approved sample [ref], kiln-dried to a moisture content of [x]% [+/- y]% at dispatch. Supplier to confirm in writing before order that the board is suitable for [the room, with / without underfloor heating] at this width and cut. Fixed [bonded / nailed to joists] to the subfloor in [ref]. Standard: BS EN 13226, declaration of performance to be supplied.

Engineered [European oak] flooring, [multi-layer, birch-plywood core], total thickness [15] mm, hardwood wear layer [4] mm measured above the tongue and groove, [190] mm face width, [random lengths from 1.5 m], [flat-sawn], grade as approved sample [ref], moisture content [x]% [+/- y]% at dispatch. Supplier to state in writing: core material and build with a section drawing; the usable depth above the tongue and groove and the maximum number of sandings it recommends; suitability over underfloor heating at this width and cut. Fixed fully bonded with the adhesive named by the supplier. Standard: BS EN 13489 (edition [ ]), declaration of performance to be supplied.

Please confirm in writing for [product ref]: (1) construction, core material and a section drawing with layer thicknesses; (2) wear layer thickness above the tongue and groove, and the number of sandings you recommend; (3) maximum recommended width for [the room / underfloor heating]; (4) moisture content at dispatch and your acclimatisation instructions; (5) species and cut, with the test used for the cut; (6) the standard the product is supplied to, and the edition.

Standards and sources

• US Forest Products Laboratory, Wood Handbook (FPL-GTR-282, 2021), chapter 4: Table 4-3 and equation 4-9. Read. Source of the oak movement chart.
• NWFA/NOFMA International Standards for Unfinished Solid Wood Flooring: National Wood Flooring Association (US). Read. Source of the 3/4 in solid thickness.
• NWFA Installation Guidelines, Appendix H (revised February 2016), and Hardwood Floors magazine (NWFA), 2017 and 2025 articles: Read. Source of the heating levers, proportional shrinkage, dry-cupping and sanding depth.
• BS EN 13226, BS EN 13489, BS EN 14342:2013 and BS 8201:2011: product standards for solid and multi-layer parquet, marking, and the UK installation code. Named; not read. BSI lists BS EN 13489:2017 as withdrawn on 7 July 2023: check the current edition.

Questions we are asked

What is the difference between solid and engineered wood flooring?

A solid board is one piece of timber, the same species from face to back. An engineered board has a real hardwood wear layer bonded to a core of other timber whose layers are arranged to restrain each other. Both can be the same species, pattern and finish. The differences are movement, how many times the surface can be sanded, and where the floor can be laid.

How thick should the wear layer on engineered flooring be?

Sources disagree. The NWFA's magazine reports engineered wear layers from about 1.6 to 6.4 mm and advises against sanding below 2.4 mm; a UK retailer says 4 mm is the minimum for sanding comparable to solid. On the magazine's figures a 3 mm layer allows one light sand, 4 mm two or three, and 6 mm three to five. Ask the maker for the usable depth in writing.

How many times can engineered flooring be sanded?

There is no standard count. A traditional sand removes about 0.8 to 1.6 mm, and one UK retailer says about 1 mm. That makes the count depend on the wear layer: from a single light sand for 3 mm to three to five for 6 mm on our arithmetic. Check the maker's own figure and the flatness and machine used.

What does 14/3 mean on an engineered floor?

It is one UK retailer's notation for a board 14 mm thick overall with a 3 mm hardwood wear layer. Notation varies by maker, so ask for both thicknesses in millimetres and how the wear layer is measured.

Can you tell engineered from solid once it is laid?

Not by looking, if the species, cut, grade, pattern and finish match. The difference shows in how the floor behaves: engineered boards move less across their width, and a solid board can be sanded more times.

Is solid wood flooring suitable over underfloor heating?

It can be, but within tight limits, and makers differ. The NWFA's guidance favours engineered construction, quarter-sawn or rift-sawn cuts and narrow boards over heating. Get the maker's written approval for the width, cut and fixing before you specify it.

Does engineered wood flooring still move?

Yes, less than solid, but it is not immune. The NWFA's magazine says engineered flooring still reacts to low humidity and can dry-cup, and in severe cases the wear layer can separate from the core. The room conditions matter for both constructions.