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Nail, Glue or Float Engineered Hardwood? The Three Methods Over Plywood, Over a Slab and Over Radiant Heat, What Each Feels Like Underfoot and What Each Costs
Flooring & Tile
Nail It, Glue It or Float It? The Subfloor Decides Most of It, the Budget Decides the Rest, and the Heated Slab Takes One Option Away
Engineered hardwood is the only wood floor that gives you a choice of how it goes down. Nail it to plywood and it feels like a traditional hardwood floor. Glue it to concrete and it feels like a traditional hardwood floor on a basement slab, which is a trick solid wood cannot do. Float it on a pad and it goes in fast for the least money and sounds a little hollow when the dog runs across it. The labour is $5.50, $7.50 and $4.00 a square foot in that order. Here is what each one needs under it, what it does over radiant, and a 500 sq ft room priced all three ways.
The three methods side by side
| Nail-down | Glue-down | Floating | |
|---|---|---|---|
| Labour, per sq ft | $5.50 | $6.50 + $1.00 adhesive = $7.50 | $4.00 (+ $0.35 poly on concrete) |
| Needs under it | 3/4 in. plywood or 23/32 OSB, dry, flat to 3/16 in. in 10 ft | Concrete under 75% RH or 3 lb MVER, or plywood; flat to 3/16 in. in 10 ft, clean and dust-free | Anything flat and dry: concrete with poly, plywood, old vinyl, old tile |
| Plank thickness | 1/2 in. and up (3/8 can be nailed with the right cleat) | Any | Click or tongue-and-groove with a glued joint; most makers want 1/2 in. or thicker over 5 in. wide |
| Feel and sound | Solid. The reference. | Solid, quietest of the three on concrete | Slightly hollow, a tap on bare pad; attached cork or a good underlay helps |
| Over radiant heat | Yes over plywood sleepers or a wood subfloor over the tubing; not into a slab | Yes, the one I prefer over a heated slab | Yes, most products; the pad adds a little R-value |
| Expansion gap | 1/2 to 3/4 in. at walls | 1/2 in. at walls | 1/4 to 3/8 in. at walls, T-mould every 30 to 40 ft of run |
| Repair one board | Cut out, glue in a replacement | Hardest; chisel it off the adhesive | Easiest at the edges, same as glue in the middle |
| Best for | Main and upper floors of a framed house | Basements, slab-on-grade, heated slabs, anywhere you want it to feel nailed and cannot nail | Budget jobs, rental units, over old floors you do not want to remove, DIY |
Material is the same for all three at a given grade; engineered hardwood costs has the grade ladder. Solid hardwood only nails, which is most of what the engineered vs solid page comes down to.
Nail-down
A pneumatic nailer drives an L-cleat or a staple through the tongue at an angle into the plywood every 6 to 8 in. The plank is held hard to the subfloor along its whole length, so it cannot flex, cannot drum and does not move as a unit; each board moves on its own, which spreads seasonal movement out into the hairline gaps the cupping and gaps page describes. It wants a wood subfloor, 3/4 in. plywood or 23/32 OSB, screwed down tight so there are no squeaks to find later. On 5/8 in. subfloor the cleats do not get enough bite and the NWFA guidelines want a layer of plywood added first, $2.75 a square foot for 3/8 in., which usually makes gluing or floating the better plan.
This is the method for the main floor of a framed house, and it is the one most installers are fastest at, which is why it costs less than gluing. Rosin paper or a felt underlayment goes down first to stop the boards squeaking against the plywood; it is not a vapour barrier and should not be.
Glue-down
A urethane adhesive is trowelled onto the slab and the planks are set into it, row by row, and rolled or weighted while it cures. The right adhesive (the manufacturer’s spec sheet names the acceptable ones, and a good one costs the $1.00 a square foot in the rate) also acts as the moisture barrier, which is why glue-down is allowed on a slab that passes the test and poly is not needed. Done well it is the quietest, most solid-feeling floor you can put on concrete, and it is what I put on heated slabs in the houses I build.
It is also the least forgiving method. The slab has to be flat to 3/16 in. in 10 ft because the plank will follow every hump and hollow, and that often means $2.00 of grinding or $3.00 of self-levelling first. It has to be clean, and curing compounds and old adhesives have to come off. The slab has to be under 75% RH by probe or 3 lb by calcium chloride, or you pay $4.00 a square foot for an epoxy moisture mitigation coat first, or you float instead. And once it is down, it is down; taking up a glued floor is $2.00 a square foot of scraping. Concrete moisture testing applies word for word.
Floating
The planks click or glue to each other at the joints and sit on a thin foam or cork pad with nothing holding them to the subfloor. The whole floor becomes one sheet that expands and contracts as a unit, which is why it needs a 1/4 to 3/8 in. gap at every wall, cabinet and pipe, covered by baseboard or quarter-round, and a T-moulding at doorways and anywhere a run goes past 30 to 40 ft. Skip the gap and the floor buckles in July; skip the T-mould on a long hallway into a great room and it peaks at the joints. The floating floor problems page is a catalogue of exactly those two mistakes.
Its advantages are real: $4.00 labour, no adhesive, no nailer, goes over an old vinyl floor or a slab with a $0.35 taped poly vapour retarder, and a competent homeowner can do it. Its disadvantages are the sound (a slight hollow tap, improved a lot by a quality pad or an attached cork backing), the fact that heavy islands and pianos pin the floor and have to be allowed for, and that most makers limit floating to planks 1/2 in. and thicker when the width goes past 5 in.
Over radiant heat
All three work over radiant with the right product, and the temperature question is the same for all: the sheet says 27 to 29 C at the surface and the warranty rides on it; our slabs run 40 C water and a 30 to 37 C surface, and have for thirty years. Over a slab with tubing in it you cannot nail, so it is glue or float. I glue, because glue puts the wood in direct contact with the concrete and heat moves through it best; a floating floor has a pad under it that is a small insulator, and a dry-air gap, and the room takes a little longer to come up. Both are approved by the Canadian mills for most of their engineered lines. Over a wood subfloor with radiant panels or tubing in sleepers below it, nailing is fine as long as the cleats are shorter than the distance to the tubing, which is a conversation to have with the heating contractor before the nailer comes out.
The humidity window matters more over radiant because the heat dries the wood from below in winter. The radiant compatibility article has the temperature rule, engineered over radiant covers species and widths, and the compatibility checker gives a yes, no or conditions for your product and system. The heated ICF slabs themselves are what we build at ICFhome.ca, and the heat loss design that sets the water temperature comes from OntarioHeatLoss.ca.
A 500 sq ft family room, three ways
Mid-grade 7-in. engineered oak at $5.25, 550 sq ft ordered. The nail-down line assumes a plywood subfloor; the other two assume a tested, flat slab.
| Line | Nailed | Glued | Floated |
|---|---|---|---|
| Material, 550 sq ft at $5.25 | $2,887.50 | $2,887.50 | $2,887.50 |
| Labour, 500 sq ft | at $5.50 = $2,750 | at $7.50 = $3,750 | at $4.00 = $2,000 |
| Taped poly, 500 sq ft at $0.35 | – | – | $175 |
| Delivery | $150 | $150 | $150 |
| 2 transitions at $35 | $70 | $70 | $70 |
| Before HST | $5,857.50 | $6,857.50 | $5,282.50 |
$1,575 between the glued and the floated floor on the same slab. The glued one feels like hardwood and heats better; the floated one is the right call when the slab is marginal, the budget is tight, or the room is a rental. The flooring cost calculator runs all three for your rooms.
Questions people ask
Is it better to glue or float engineered hardwood?
Glue for feel, sound and radiant performance, on a slab that passes a moisture test and is flat. Float for cost, speed, a marginal slab or an old floor you are covering. Nail when you have a plywood subfloor and no tubing in it.
Can you nail engineered hardwood?
Yes, 1/2 in. and thicker planks nail to 3/4 in. plywood with a cleat nailer the same as solid, and 3/8 in. products nail with a smaller cleat. You cannot nail into concrete or into a subfloor with radiant tubing in it.
Does a floating floor feel cheap?
It sounds a little hollow compared with a nailed or glued floor, and heavy footsteps carry. A thicker plank, a cork or rubber pad instead of foam, and a flat subfloor close most of the gap. Over a slab, people who do not know what they are listening for rarely notice.
Which method is best over radiant floor heating?
Glue-down for a slab with tubing in it, for heat transfer and because the wood is coupled directly to the concrete. Floating is approved for most products and is the fallback when the slab is marginal. Whichever you choose, know the surface temperature; the sheet’s 27 to 29 C cap is where the warranty stops.
How much more does glue-down cost than floating?
$3.50 a square foot of labour: $7.50 including adhesive against $4.00. On a 500 sq ft room that is $1,750, less the $175 of poly the floating floor needs on concrete.
Check your floor and your heat first
The radiant flooring compatibility checker tells you whether your plank and your heating system get along, and which method the manufacturer allows. Then the flooring cost calculator prices it nailed, glued or floated.
Sources and further reading
- National Wood Flooring Association: the installation guidelines every hardwood warranty points to: subfloor flatness, moisture limits, acclimation, fastening schedules and the radiant-heat chapter.
- Uponor Canada: hydronic radiant tubing and controls; their design manual is where the surface temperature and floor R-value tables come from.
- ICFhome.ca: where I build the ICF houses and heated slabs these details come from.
