Hardwood Flooring Installation Guide

Complete guide to hardwood flooring installation including acclimation requirements, subfloor preparation, nail/staple spacing, expansion gaps, underlayment selection, and professional finishing techniques.

Acclimation Requirements

Critical Acclimation Guidelines

Proper acclimation prevents cupping, crowning, gapping, and buckling after installation. Never skip this step.

Time Requirements

• Minimum: 3-5 days
• Recommended: 7-14 days
• Engineered: 3-5 days minimum
• Solid 3/4": 7-14 days minimum
• Exotic species: 14+ days

Environment Conditions

• Temperature: 60-80°F constant
• Humidity: 35-55% relative humidity
• HVAC: Must be operational
• Storage: Lay flat, stacked with spacers
• Location: In room of installation

Moisture Content by Humidity Level

Humidity Level	Target MC %	Acceptable Range	Climate Zone
25-35% RH (Dry)	6-7%	5-8%	Desert, High Altitude
35-45% RH (Normal)	7-9%	6-10%	Most US Regions
45-55% RH (Moderate)	9-11%	8-12%	Coastal, Humid Areas
55-65% RH (Humid)	11-13%	10-14%	Southeast, Gulf Coast

Subfloor Moisture Requirements

Wood Subfloor (Plywood/OSB)

Maximum MC: 12% moisture content
MC Difference: Within 4% of flooring MC
Flatness: 1/8" in 6 feet, 3/16" in 10 feet
Thickness: Minimum 5/8" thick plywood or 23/32" OSB
Gaps: 1/8" expansion gaps between panels

Concrete Subfloor

Maximum MC: 3 lbs/1000 sq ft/24 hrs (CaCl test)
RH Test: 75% or less relative humidity
Age: Minimum 60 days cured (90 days recommended)
Flatness: 1/8" in 10 feet maximum deviation
Sleeper System: Required for solid hardwood on concrete

Testing Methods

Wood: Pin Meter

Insert pins 1/3 depth of subfloor, test in 5+ locations

Concrete: Calcium Chloride

72-hour test, measures moisture vapor emission rate

Concrete: RH Probe

More accurate, measures humidity at 40% depth

Nail/Staple Spacing & Patterns

Fastener Specifications by Floor Width

Floor Width	Fastener Type	Spacing Along Board	Distance from End
1.5" - 2" strip	18-gauge 1.5" staples or 2" cleats	8-10 inches	1-2 inches
2.25" - 3.25" strip	18-gauge 2" staples or 2" cleats	8-10 inches	1-3 inches
3.25" - 5" plank	16-gauge 2" staples or cleats	6-8 inches	2-3 inches
5"+ wide plank	15-gauge 2" staples, may need glue assist	4-6 inches	2-3 inches

Fastening Best Practices

Blind nail at 45-50 degree angle through tongue
First and last 3 rows: top nail or screw, then putty
Fasteners must penetrate subfloor by 1 inch minimum
Two fasteners per plank at each joist for 5"+ planks
Adjust nailer pressure to prevent overdriving
Use manual nailer for last 12-18 inches of rows

Common Fastening Mistakes

Overdriving fasteners (damages tongue/groove)
Underdriving (boards not secured, squeaks develop)
Spacing fasteners too far apart (cupping, movement)
Not fastening near ends (end joint separation)
Wrong angle (splits tongue or misses subfloor)
Using too short fasteners (insufficient penetration)

Expansion Gap Requirements

Why Expansion Gaps Matter

Wood expands and contracts with humidity changes. Without proper gaps, floors will buckle, crown, or develop cupping. Expansion gaps must be left at all fixed vertical surfaces (walls, cabinets, posts).

Expansion Gap Sizing by Room Dimension

Room Dimension	Solid 3/4" Hardwood	Engineered Hardwood	Notes
Up to 20 feet	1/2 inch	1/4 inch	Standard rooms, closets
20-30 feet	3/4 inch	3/8 inch	Large rooms, open concept
30-40 feet	1 inch	1/2 inch	Great rooms, commercial
Over 40 feet	1-1/4 inch+	5/8 inch+	May need transition strip

Additional Gap Requirements

Doorways: 1/2" under door, use T-molding
Cabinets/Islands: Same as perimeter walls
Stairs: 1/2" at all nosing/riser connections
Hearths: 3/4" minimum around fireplace structures
Posts/Pipes: 1/2" all around, use escutcheon plates

Climate Considerations

Humid climates: Add 25% to gap size
Dry climates: Use minimum recommended gap
Seasonal swings: Base on worst-case humidity
Wide planks 5"+: Increase gaps by 50%
Exotic species: May need larger gaps (check specs)

Underlayment Selection

15 lb Felt Paper

Traditional, economical

• Best for: Solid nail-down flooring
• Cost: $0.15-0.25 per sq ft
• Moisture barrier: Minimal
• Sound dampening: Minimal
• Installation: Staple down, overlap 4"
• Lifespan: Same as floor

Rosin Paper

Red building paper

• Best for: Solid over wood subfloor
• Cost: $0.10-0.20 per sq ft
• Moisture barrier: None
• Sound dampening: Minimal
• Installation: Asphalt-saturated, staple
• Note: Not vapor barrier

Foam Underlayment

2-3mm foam sheets

• Best for: Engineered floating floors
• Cost: $0.25-0.50 per sq ft
• Moisture barrier: With vapor barrier backing
• Sound dampening: Good (IIC 65-70)
• Installation: Tape seams
• Additional: Some have attached vapor barrier

Cork Underlayment

Premium option, 3-6mm thick

• Best for: Sound reduction, floating engineered
• Cost: $0.75-1.50 per sq ft
• Moisture barrier: Need separate vapor barrier
• Sound dampening: Excellent (IIC 70-75)
• Installation: Tape or glue seams
• Benefits: Eco-friendly, thermal insulation

Vapor Barrier (Poly)

6-mil polyethylene sheeting

• Required: Over concrete subfloors
• Cost: $0.10-0.15 per sq ft
• Moisture barrier: Excellent
• Sound dampening: None
• Installation: Overlap 8", tape seams, run up walls 3"
• Note: Use under felt/foam on concrete

Selection Guide by Installation Method

Nail-down solid hardwood over wood subfloor: 15 lb felt or rosin paper
Nail-down solid hardwood over concrete (with sleepers): 6-mil poly vapor barrier, then felt
Glue-down engineered over concrete: 6-mil poly vapor barrier (check adhesive compatibility)
Floating engineered over wood subfloor: Foam underlayment with integrated vapor barrier
Floating engineered over concrete: 6-mil poly vapor barrier, then foam underlayment
Sound reduction priority: Cork underlayment (with separate vapor barrier if needed)

Board Staggering Patterns & Layout

Critical Staggering Rules

• Minimum offset: 6 inches between end joints in adjacent rows
• Recommended offset: 8-10 inches for best appearance
• Pattern requirement: No H-joints (4 corners meeting)
• Stair-stepping: Avoid stair-step patterns (looks unnatural)
• Random appearance: Vary lengths to create random look

Layout Best Practices

Run boards perpendicular to floor joists when possible
Run boards parallel to longest wall for best appearance
Start with straightest wall (check for square)
Rack out 6-8 rows dry to plan cuts and stagger
Mix boxes to blend color/grain variation
Save cutoffs 12"+ for use in other rows

Common Layout Mistakes

Starting without checking room square (compounds errors)
Not planning for last row width (avoid slivers under 2")
Creating repetitive patterns (looks manufactured)
Insufficient stagger (weak joints, visible pattern)
Not planning doorway transitions in advance
Wasting material by not using cutoffs efficiently

Transition Strip Types & Applications

T-Molding

Same height transitions

• Between rooms (hardwood to hardwood)
• Doorways with same floor height
• Allows expansion on both sides
• Height: Matches floor thickness
• Installation: Track or glue-down

Reducer Strip

Height change transitions

• Hardwood to vinyl/carpet (lower)
• Creates gentle slope
• Prevents trip hazard
• Available in various heights (1/4"-3/4")
• Installation: Screw or glue to subfloor

Threshold/Baby Threshold

Doorway transitions

• Exterior doorways
• Slight height differences (1/8"-1/4")
• Weather seal at exterior doors
• Flat or beveled edge
• Installation: Screws into subfloor

Stair Nosing

Stair tread edge

• Stairs, landings, step-downs
• Provides finished bullnose edge
• Safety: prevents slip-off
• Flush or overlap style
• Installation: Nails/screws from top

End Cap/Flush Reducer

Floor edge finishing

• Hardwood ending at sliding doors
• Finishing edge at transitions to tile
• Creates smooth edge profile
• Flush mount to floor surface
• Installation: Glue or brad nail

Quarter Round/Shoe Molding

Perimeter wall coverage

• Covers expansion gap at baseboard
• Hides imperfect cuts at walls
• Quarter round: 90° radius
• Shoe: flatter profile, more flexible
• Installation: Nail to baseboard, not floor

Installation Tips

• Always match species/stain to flooring when possible
• Leave 1/16" gap on each side of T-molding for expansion
• Pre-drill screw holes to prevent splitting
• Use color-matched putty for nail holes in visible areas
• Install transitions after flooring is complete and acclimated
• For track systems, ensure track is level and secure before clicking in molding

Step-by-Step Installation Process

Acclimate Flooring & Test Moisture

•Deliver flooring to jobsite 7-14 days before installation
•Maintain constant 60-80°F temperature and 35-55% humidity
•Stack boxes flat with spacers for air circulation
•Test flooring MC with moisture meter (target within 4% of subfloor)
•Test subfloor: Wood <12% MC, Concrete <3 lbs/1000 sq ft/24hr

Prepare & Inspect Subfloor

•Remove all existing flooring, carpet, padding, and debris
•Fix squeaks by screwing subfloor to joists (avoid nails)
•Check flatness: 1/8" in 6 feet maximum deviation
•Sand high spots or fill low spots with floor leveler
•Replace damaged subfloor sections; secure all loose areas
•Ensure subfloor panels have 1/8" expansion gaps

Install Underlayment/Vapor Barrier

•Over concrete: Install 6-mil poly, overlap 8", tape all seams
•Over wood subfloor: Roll out 15 lb felt or rosin paper
•Staple underlayment every 6-8 inches (don't over-staple)
•Overlap seams by 4 inches minimum
•Run vapor barrier up walls 3 inches, trim after installation
•Ensure smooth, wrinkle-free underlayment before proceeding

Plan Layout & Check Room Square

•Measure room: find center or determine starting wall
•Check walls for square using 3-4-5 triangle method
•Snap chalk line for first row (parallel to longest wall)
•Calculate last row width (must be at least 2 inches)
•If last row will be too narrow, rip first row to balance
•Plan doorway transitions, fireplace clearances, and obstacles

Install First Three Rows

•Face nail or screw first row 1/2" from wall (pre-drill)
•Leave proper expansion gap (1/2"-3/4" depending on room size)
•Blind nail second row at 45° angle through tongue
•Use flooring nailer starting on row 3
•Stagger end joints minimum 6 inches between rows
•Use scrap boards to protect tongues when tapping together

Continue Field Installation

•Rack out 6-8 rows ahead to plan cuts and color variation
•Maintain consistent 6-10 inch fastener spacing (varies by width)
•Tap boards tight using tapping block on groove side
•Sight down rows frequently to ensure straightness
•Use pull bar to tighten end joints in each row
•Adjust nailer pressure if overdriving or underdriving

Cut Around Obstacles & Doorways

•Undercut door jambs 1/16" higher than flooring thickness
•Use jamb saw or oscillating tool for clean cuts
•Create cardboard template for complex cuts (vents, pipes)
•Leave 1/2" expansion gap around all fixed obstacles
•Use coping saw or jigsaw for intricate curved cuts
•Dry fit pieces before final installation

Install Last Rows & Secure

•Measure and rip last row to width (include expansion gap)
•Face nail or screw last row (pre-drill to prevent splits)
•Use pry bar to pull boards tight to previous row
•For tight spaces, remove bottom of groove and glue down
•Set all face nails below surface with nail set
•Fill face nail holes with color-matched wood putty

Install Transitions & Moldings

•Install threshold/T-molding at doorways (use track if available)
•Install reducer strips at height transitions
•Install stair nosing on steps and landings
•Install quarter round or shoe molding at baseboards
•Nail moldings to wall/baseboard, NOT to floor
•Use color-matched putty for visible nail holes

Final Inspection & Cleanup

•Inspect entire floor for loose boards, raised nails, gaps
•Re-fasten any areas that feel loose or squeaky
•Vacuum thoroughly to remove all dust and debris
•Wipe down with microfiber mop (slightly damp, never wet)
•Wait 24-48 hours before moving furniture back
•Educate homeowner on proper cleaning and maintenance
•Provide warranty information and care instructions

Best Practices & Common Mistakes

DO:

Always acclimate wood to jobsite conditions (7-14 days minimum)
Test moisture content of both flooring and subfloor before starting
Mix boards from multiple boxes to blend color variation
Rack out several rows ahead to plan layout and stagger
Use proper expansion gaps (minimum 1/2" at all walls)
Follow manufacturer fastener spacing recommendations exactly
Keep HVAC running during and after installation
Inspect each board for defects before installing

DON'T:

Install hardwood over concrete without proper moisture barrier
Skip moisture testing (causes 90% of flooring failures)
Install flooring immediately upon delivery without acclimation
Nail moldings to the floor (prevents expansion, causes buckling)
Use insufficient expansion gaps (floors will buckle in humidity)
Install over uneven subfloor (creates squeaks and hollow spots)
Overdrive or underdrive fasteners (damages boards or creates squeaks)
Create H-joints or insufficient stagger (weak installation)