Hardwood Flooring Installation: Subfloor & Method Guide

The floor starts below the planks. An installation can look perfect on handover and still fail if the substrate is damp, unsuitable or outside the product’s flatness requirements. This is a buyer and homeowner planning guide, not a substitute for the exact product’s instructions or a qualified installer’s site assessment. NWFA’s installation guidelines say not to install over a known moisture condition and to follow the flooring manufacturer’s requirements.[1]

Start with four facts: Is the room on, above or below grade? Is the substrate wood or concrete? Is there radiant heat? Which installation methods does the specific flooring model allow? If you cannot answer those, defer selecting adhesive, underlayment or a start date.[1][14]

Jump to: subfloor decision map · three installation methods · pre-installation sequence · condo and stairs · installer handoff.

Room and subfloor decision map

Site condition	First question to resolve	Do not assume
Wood subfloor, dry on or above grade	Does it meet the product’s type, thickness, fastening, flatness and moisture requirements?[1]	That every solid or engineered plank can use the same fasteners.
Concrete slab, including a slab on grade	Which wood products and systems explicitly permit this slab, and what moisture tests and limits apply?[1][14]	That a slab is dry because its surface looks or feels dry.
Below-grade finished room	Is water intrusion ruled out and is this exact product/assembly approved below grade?[1]	That “engineered” means waterproof or that a floating floor repairs a damp foundation.
Radiant-heated floor	Is the floor model approved for this heat system, substrate and installation method, with documented controls and limits?[1][14]	That all engineered species or adhesives are suitable for radiant heat.
Condo or multi-unit dwelling	What acoustic, fire, moisture and construction rules apply to this unit and floor assembly?	That an underlayment’s lab rating guarantees the assembled floor complies with building rules.

For a construction-level decision, see engineered versus solid; for the seasonal living conditions a wood floor will encounter, see hardwood in Canada’s climate.[1][2]

Nail, glue or float is a product-specific choice

Nail or staple: A mechanical attachment to a suitable wood substrate. Fastener type, spacing, plank width, substrate and any supplemental adhesive are specified by the product and installation system. Do not drive fasteners into an unsuitable concrete slab or assume a floor approved for glue-down can also be nailed.[1][14]

Glue-down: A compatible adhesive bonds an approved floor to a prepared substrate, often relevant for engineered flooring over concrete. Ask for the flooring, adhesive and moisture-control system together, including preparation, coverage and their published limits. Adhesive is not a licence to ignore a known moisture problem. A Canadian manufacturer’s FAQ permits some engineered products over concrete using its recommended systems while advising against its 3/4-inch solid floor directly over concrete; that example does not approve other brands.[1][14]

Floating: Approved planks form a floor that is not attached directly to the substrate. The joint, underlayment or membrane, maximum continuous area, transitions and perimeter clearances have to follow the exact system. Not every engineered board may be floated: even within one manufacturer’s range, the FAQ limits floating to certain products and widths.[1][14]

When buying underlayment, make the seller name the entire compatible assembly. Acoustic claims may depend on a tested system, and the required vapour-control layer depends on slab, grade and floor instructions; thicker or softer is not automatically better. See underlayment for the category, not as a substitute for a product-specific specification.[1][14]

Six checkpoints before the first board

1. Make the building ready. Address leaks and other wet work; operate the indoor conditions expected during normal occupancy. Confirm the maker’s temperature and relative-humidity requirements before material is delivered. Never plan to install wood while a room is still drying out.[1]
2. Identify and inspect the substrate. An installer should assess structural soundness, fastening, cleanliness, flatness and existing layers. An old floor or resilient covering is not automatically an approved base: the manufacturer must permit the assembly. Hidden damage changes the scope and possibly the schedule.[1][14]
3. Measure and record moisture. Test a wood subfloor or concrete with the method appropriate to the selected floor/assembly and compare against the maker’s limits; also record room conditions and flooring moisture as required. Ask for the readings and locations, not merely a verbal “pass.” A wall hygrometer cannot certify a concrete slab.[1]
4. Condition material to the site. Follow packaging/storage instructions for that model. The NWFA defines acclimation as aligning the wood and the expected in-use environment; where measurements already align, installation can sometimes begin immediately. A fixed number of days alone cannot fix a wet substrate. One manufacturer asks that certain cartons remain sealed while stored in the room: another product may instruct otherwise.[1][14]
5. Confirm layout and details. Agree plank direction, starting line, staggering/pattern, expansion space, door undercuts, fixed cabinetry and transitions. Resolve stair construction and trim selection before the main floor height is locked in. The required clearances are system-specific.[1]
6. Stop if the site fails. A failed moisture/flatness check, fresh leak or incompatible floor should trigger a documented remedy and a new schedule or product choice. Do not sign off on a waiver that asks an installer to ignore known conditions.[1]

A professional installer can explain which test, limit and product instruction supports the proposed method. NWFA also highlights subfloor preparation, irregular rooms, tooling and job safety as common reasons a seemingly simple DIY project becomes difficult.[15] On FlooringInstallers.ca, you can begin looking for an installer; a directory listing is not a certification or verification by us. Independently check references, insurance, experience with the specific floor and written scope before hiring.

Edges, stairs, condos and other scope traps

• Thresholds: Mark every meeting with tile, carpet, existing wood or an exterior door. The finishing profile depends on relative heights and on whether one floor floats. Order or specify compatible transitions before installation starts.[1]
• Stairs: Ask whether the quote includes treads, risers, approved stair nosing, finish matching and safe detailing. A plank intended for flat floors is not itself a finished stair edge.[1]
• Baseboards and doors: Decide whether trim is removed and reinstalled or a separate finishing piece covers the perimeter. Plan door clearance after the full assembly height, not only plank thickness, is known.
• Condos: Ask your building for its written alteration and acoustic requirements before ordering. Obtain any required approvals and choose a tested system acceptable under those rules; no generic product claim can establish compliance for your building.
• Radiant heat: Obtain the exact product’s heat-system approval, commissioning schedule, controls and temperature limits from its documentation. Have the heating trade and flooring installer agree on the assembly in writing.[1][14]

A handoff record worth keeping

Before the crew leaves, keep copies of:

• Product manufacturer, exact model/colour, carton or lot information and the applicable installation/care documents.
• Dated room temperature/RH, moisture-test results and substrate notes; any rectification and retest.[1]
• Subfloor type; method used; named adhesive, membrane, underlayment or fasteners; transitions and expansion details.[1]
• The agreed scope, change orders, any remaining defects, installation date and the point of contact for warranty questions.
• A spare matching plank/carton if arranged, stored per the maker’s instructions and labelled so a future repairer knows the original floor.

Use our quantity and cost worksheet when comparing quotes. If the room/subfloor facts are not established, send them with a quote request rather than buying an adhesive or floor on guesswork. For the parts that finish the project, browse trims and mouldings and underlayment; suitability still depends on the chosen floor.

Sources

[1] https://nwfa.org/wp-content/uploads/2026/02/NWFA-Installation-Guidelines.pdf [2] https://woodfloors.org/types-of-wood-floors [14] https://www.miragefloors.com/en-ca/faq/installing-hardwood-floors [15] https://woodfloors.org/avoid-diy-woes-hire-a-pro