What underlayment and installation techniques reduce noise when replacing carpet with hardwood?

Short answer

Use a high-density acoustic underlayment and decoupling techniques. For best footfall noise reduction, float engineered hardwood over a 3–5 mm rubber or 6 mm cork sound underlayment with a perimeter isolation gap sealed in acoustical sealant. If you’re nailing down solid hardwood, use a dedicated sound-control underlayment (wool/felt or rubber-cork composite) and fasten the subfloor thoroughly to kill squeaks. On concrete, a glue-down engineered floor with an elastomeric acoustic adhesive can perform very well. Always address subfloor flatness and add perimeter isolation to prevent noise bridging.

What to look for in an acoustic underlayment

Pick an underlayment compatible with your installation method (float, nail, or glue) and your subfloor (wood vs. concrete). Higher density and slight thickness improve impact sound reduction.

Target specs for low-noise hardwood installs:
- Underlayment type: High-density rubber (3–5 mm), cork (6 mm), or felt/composite rated for hardwood
- Impact rating: IIC ≥ 60 (multi-family often requires 60+)
- Airborne rating: STC ≥ 55 (where required)
- Vapor control (on concrete): Class I barrier, ≤0.1 perms, taped seams
- Perimeter isolation: 1/4" foam sill sealer or backer rod + acoustical sealant
- Subfloor flatness: ≤ 3/16" variation over 10 ft (≤ 1/8" preferred)

Good choices by installation method

• Floating engineered hardwood:
  • 3–5 mm rubber underlayment (excellent impact sound reduction)
  • 6 mm cork underlayment (very good; don’t over-compress)
  • Premium felt/composite underlayments approved for floating hardwood
• Nail-down solid/engineered hardwood:
  • Sound-control felt/wool underlayment (not just roofing felt) or rubber/cork composites approved for nail-down
  • Avoid soft foams that collapse under staples/cleats
• Glue-down engineered hardwood (especially over concrete):
  • Elastomeric acoustic urethane adhesive (e.g., moisture-vapor-control varieties) applied with the manufacturer’s trowel notch

Step-by-step approach

1. Assess and prep the subfloor

   • Tighten the subfloor to joists with construction screws every 6–8 in. to eliminate squeaks.
   • Verify flatness with a 6 ft straightedge. Grind high spots; fill lows with leveling compound. Hollow spots telegraph noise.
   • Moisture check: Use a pin or pinless moisture meter. For wood subfloors, aim to be within the flooring manufacturer’s MC tolerance (often within 2–4% of the flooring). On concrete, use RH or calcium chloride tests and follow adhesive/underlayment limits.

2. Plan your assembly

   • Multi-family/condo: Confirm HOA/IIC-STC requirements and choose an assembly that meets published ratings (manufacturer data sheets).
   • Choose floating if you want the best impact noise reduction with minimal structure-borne transmission.
   • If nailing down, choose a dedicated acoustic underlayment rated for nail-down hardwood.

3. Perimeter isolation

   • Install 1/4 in foam isolation strip against walls or plan to fill the expansion gap later with backer rod and acoustical sealant. This decouples the floor from walls and reduces flanking noise.

4. Underlayment install

   • Floating: Roll out rubber/cork/composite underlay perpendicular to plank direction. Tape seams with manufacturer tape. On concrete, ensure an integrated vapor barrier or add 6 mil poly with sealed seams.
   • Nail-down: Lay the sound-control felt/composite underlayment, overlapping per instructions. Avoid standard 15 lb roofing felt as your only layer; it offers minimal sound benefit.
   • Glue-down: Trowel the acoustic adhesive, maintaining the specified notch and coverage. Some systems combine a sound mat with adhesive—follow their sequencing.

5. Hardwood installation

   • Floating: Click or glue joints per manufacturer. Stagger end joints, use tapping block and pull bar to seat boards snugly without crushing the underlayment.
   • Nail-down: Use a flooring nailer with 16–18 ga cleats; follow the recommended fastener schedule (often 3–4 in. along the length, 1–2 in. from ends). Avoid over-driving which can squeak.
   • Glue-down: Maintain clean adhesive ridges; roll the floor with a 75–100 lb floor roller within the open time to ensure transfer and minimize hollow spots.

6. Finish the perimeter

   • Maintain the expansion gap. Insert backer rod where accessible and apply an acoustical sealant; then install baseboard and shoe molding fastened to the wall, not the floor, to avoid bridging.

7. Aftercare for quieter rooms

   • Add area rugs with dense felt pads in high-traffic zones. Install felt glides under furniture.

Tools and materials

• Moisture meter (pin/pinless), 6 ft straightedge, chalk line
• Circular or miter saw, oscillating multi-tool (for undercutting jambs)
• Flooring nailer (for nail-down), dead-blow mallet, tapping block, pull bar
• Notched trowel and 75–100 lb roller (for glue-down)
• Construction screws, drill/driver, countersink bit
• Acoustic underlayment (rubber/cork/felt/composite as specified)
• 6 mil poly (if needed), seam tape, acoustical sealant, backer rod, foam sill sealer
• PPE: respirator for dust/adhesive fumes, safety glasses, hearing protection, knee pads

Cost and time

• Underlayment: $0.50–$2.50 per sq ft (felt/composite on the lower end; high-density rubber on the higher end)
• Acoustic adhesive: $1.50–$3.50 per sq ft
• Labor/DIY time: A typical 300 sq ft room takes 1–2 days for prep and install, not counting extensive leveling.

Tips for best results

• Heavier, denser underlayments generally reduce impact noise better than thin foams.
• Glue-down with an acoustic urethane can outperform nail-down for noise on concrete slabs and helps with moisture control.
• Always verify the underlayment is approved by your flooring manufacturer to preserve warranties.
• Keep thickness reasonable (usually ≤ 5–6 mm). Too soft or thick can cause joint movement and squeaks.

Common mistakes

• Skipping subfloor screw-down and flatness—number one cause of squeaks and hollow sounds.
• Using the wrong underlayment for nail-down floors (soft foam collapses under fasteners).
• Forgetting a vapor barrier over concrete, leading to moisture issues and noise from debonding.
• Bridging the expansion gap with caulk or nailing base directly into the floor—this transmits sound.
• Ignoring HOA acoustic requirements.

When to call a pro

• Condo or multi-family projects where documented IIC/STC compliance is required
• Glue-down installs over concrete, especially with vapor concerns
• Significant subfloor leveling/structural movement
• Radiant-heated slabs or moisture readings outside manufacturer limits

By pairing a quality acoustic underlayment with careful subfloor prep, perimeter isolation, and the right installation method for your subfloor, you can replace carpet with hardwood while keeping footfall and transmission noise to a minimum.