Wood Floor Installation Methods Compared

You can fix a wood floor in three main ways: nail or staple it to a wood subfloor, glue it down, or float it on an underlay. The right method depends on the flooring format, the subfloor, and the maker's instructions. NWFA's installation guidelines are explicit that where manufacturer instructions exist they come first, and the guidelines apply only where those are missing or refer back to them¹. This guide compares the three methods and the subfloor and expansion rules that apply to all of them.

Which flooring formats suit which installation method?

Method	Formats it suits	Notes from the sources
Nail or staple down	Solid and engineered tongue-and-groove boards over wood subfloors	Wood flooring may be nailed down over most wood subfloors except particleboard¹
Glue down	Solid boards, engineered boards and parquet over wood or concrete	Works over many substrates that meet the minimum requirements¹; Junckers glues 14 to 22 mm solid boards and planks to a dry, loadbearing subfloor⁴
Floating	Engineered flooring with tongue-and-groove or locking edges	NWFA: engineered flooring is the only type of wood floor that can be used, and solid wood should never be floated unless the maker recommends and warrants it¹
Parquet	Geometric patterns, solid or engineered, 5/16 to 3/4 inch thick	Parquet is often glued, but can be blind-nailed in a nail-assisted glue-down if an exposed side tongue remains¹

Makers do not always agree with the general rule. Junckers approves 14 and 22 mm solid 2-strip boards and 15 and 20.5 mm solid planks for a floating clip system, as well as glue-down and batten fixing². Kährs, which makes engineered floors, says its 3-layer floors can be floated or glued down on solid surfaces such as concrete, particleboard or wood⁶. Check the product's own installation sheet, because warranty depends on it.

How does nail-down installation work?

Nailing needs a wood subfloor that is sound, free from squeaks and vertical deflection, and meets NWFA's requirement for flatness of 1/4 inch in 10 feet, or 3/16 inch in 6 feet¹. Fasteners are blind-nailed through the tongue with flooring nailers. NWFA describes cleats (16, 18 and 20 gauge) and staples (for example 1/2 inch crown at 15.5 gauge) as the main fasteners¹.

Spacing depends on the product. Unless the maker says otherwise, NWFA's standard schedule for engineered tongue-and-groove flooring under 5/8 inch thick is a fastener every 3 to 4 inches along each board, with at least two per board; 3/4 inch solid strip under 3 inches wide takes 8 to 10 inch intervals¹. Where the schedule cannot be followed, for instance over heating tubes, NWFA suggests nail-assisted glue-down, full-spread glue-down or floating instead¹.

How does glue-down installation work?

Gluing bonds the floor to the subfloor, either wood or concrete. NWFA's flatness standard for glue-down is 3/16 inch in 10 feet or 1/8 inch in 6 feet on both wood and concrete¹. Junckers gives the equivalent for its glued floors as a maximum deviation of 2 mm under a 1.5 m straight edge, with 3 mm under a 2 m straight edge in the UK⁴.

Glue-down is moisture-sensitive. Junckers says a conventional damp-proof membrane cannot be used under glued hardwood, so residual moisture in the subfloor must not exceed 65% RH, and between 65 and 95% RH its liquid moisture barrier is applied before gluing⁴. NWFA's own concrete threshold is different: slabs above 80% RH by the in-situ probe test should wait or receive a Class 1 impermeable vapour retarding membrane¹. Both sets of figures are described in our moisture and acclimatisation guide.

Gluing has a practical advantage on large floors: Kährs says a glued floor has minimal expansion, so no breaks at doorways are required⁵.

How does floating installation work?

Floating floors are not attached to the substrate; the boards click or are glued to one another and move as one unit. NWFA says floated boards must have tongue-and-groove or locking edges, the subfloor must be flat to 1/8 inch in 6 feet or 3/16 inch in 10 feet, and wood flooring should not be floated on ramps or non-flat surfaces¹. Over concrete, a separate Class I vapour retarder is needed under the acoustic underlay if the underlay has none¹.

Floating floors need movement joints. NWFA requires transition pieces at doorways under 4 feet wide and in any floated area wider than 20 feet or longer than 40 feet, and says trim must be held off the floor by at least 1/16 inch and never fastened through it¹. Kährs gives a different, simpler rule of expansion gaps of at least 10 mm at doorways for floating floors⁵.

What does the subfloor need?

Whatever the method, NWFA lists the same basics: a sound substrate free from squeaks, flatness within tolerance, and a moisture test of both the flooring and the subfloor¹. Its guidance for wood subfloors is a moisture content no more than 4% above strip flooring (under 3 inches wide) and no more than 2% above plank flooring (3 inches or wider)¹. Junckers expects wooden subfloors to be in balance with room humidity at 6 to 12% moisture content, and uses a limit of 12% for floors on its clip system³.

Grade also matters: NWFA says engineered floors can be installed above, on and below grade, while solid flooring should not go below grade unless the maker agrees¹. See solid wood and engineered wood for the formats.

How much expansion gap do you leave?

Source	Rule
NWFA, nail-down, glue-down and floating	Generally equal to the thickness of the material, so 1/2 inch board needs 1/2 inch¹
NWFA, parquet	A minimum of 1/2 inch around the perimeter and obstructions¹
NWFA, end-grain	A typical 3/4 inch at vertical obstructions, plus 1/8 to 1/4 inch (3 to 5 mm) built in within the floor¹
Junckers, glued floor	1.5 mm per metre of floor width on each side and 1 mm per metre at each end, minimum 12 mm (UK: 15 mm)⁴
Junckers, clip (floating) floor	2 mm per metre of floor width on each side, minimum 12 mm (UK: 15 mm)³

The sources use different logic: NWFA sets the gap by product thickness, Junckers by room width. Where a maker states a rule for its product, use it. For wide floors, NWFA adds that spacing within the floor may be needed on spans wider than 20 feet¹. Patterns such as herringbone and end-grain blocks usually follow the parquet and end-grain rules.

What about nailed, glued and floating floors in France?

France documents each method in a separate NF DTU: 51.1 for nailed parquet, 51.2 for glued parquet and 51.11 for floating installation of multilayer parquet and wood-veneer coverings⁸. Our flooring standards guide explains how these relate to the European product standards.

Frequently asked questions

Can solid wood flooring be floated?

NWFA says solid wood should never be floated unless the flooring manufacturer recommends and warrants it, because solid wood is generally not dimensionally stable enough under seasonal change¹. Junckers does approve its solid boards for a clip-fixed floating system, so the maker's instructions decide².

How big should the expansion gap be?

NWFA says the gap is generally equal to the thickness of the flooring, so a 1/2 inch board needs 1/2 inch¹. Junckers instead sizes the gap by room width, at 1.5 mm per metre of width each side for glued floors with a minimum of 12 mm⁴.

How flat does the subfloor need to be?

NWFA gives 1/4 inch in 10 feet for nail-down over wood, and 3/16 inch in 10 feet or 1/8 inch in 6 feet for glue-down, floating and parquet installations¹. Junckers specifies 2 mm under a 1.5 m straight edge for glued floors⁴.

Which installation method is used over underfloor heating?

NWFA describes nail-down, glue-down and floating methods over radiant heat, each with conditions; Weitzer says full-surface bonding gives the best heat transfer, and floating is suitable only to a limited extent¹⁷. See our underfloor heating guide.

What are the French installation standards?

The DTU list gives NF DTU 51.1 for nailed parquet, 51.2 for glued parquet and 51.11 for floating installation of multilayer parquet and wood-veneer coverings⁸.