Demand for interior secondary windows—often called double windows in Japan—is accelerating again. Households now expect dual value: quieter rooms and lower utility bills, pushing 2025 domestic shipments to 112% year-on-year (Japan Sash Association monthly statistics).
This market brief summarizes the latest Japan-specific trends, leading manufacturer offerings, subsidy programs, installation effects, and outlook for soundproof-focused renovations.
Market Snapshot: Interior Secondary Windows in Japan#
Adoption and Demand Segments#
- The Ministry of Land, Infrastructure, Transport and Tourism (MLIT) “Housing Renovation Survey 2024” shows interior window installation rates reaching 22.4% in greater Tokyo condominiums. 46% cite soundproofing as the primary objective, ahead of insulation (38%) and security (11%).
- High sound insulation (SRI T-2 or higher) models now account for 31% of shipments, up nine points from 2023, driven by remote work and lifestyle noise concerns.
- Japan’s renovation market increasingly bundles secondary windows with insulation upgrades, treating them as core components of “energy + quiet” remodeling packages.
Regulatory Tailwind: 2025 Energy Code Revision#
Japan’s April 2025 Building Standards Law revision strengthens disclosure of energy performance in existing homes. Since window performance is now a scored item, secondary windows directly contribute to asset-value appraisals.
- MLIT simulations estimate whole-home energy consumption can drop 8–12% when every window gains an interior sash.
- The Tokyo Metropolitan Government “Quiet Housing Model 2024” recorded an average 12 dB reduction in road-noise experiments for condominiums along major arterials.
Doubling Value: Soundproofing Plus Insulation#
| Value Axis | Expected Benefit | Key KPI |
|---|---|---|
| Sound Insulation | Mitigate traffic and neighborhood noise | Indoor noise level (dB), SRI grade T-2/T-3 |
| Thermal Efficiency | Lower HVAC costs and condensation | Annual electricity bill, surface temperature, UA improvement |
Points to Emphasize#
- Sound Control: Interior sashes and airtight frames suppress 10–15 dB in target frequency bands, particularly noticeable along rail lines and highways.
- Energy Savings: Pairing with Low-E insulated glass pushes heat transmittance from 2.33 to 1.7 W/m²K (YKK AP test data).
- Condensation Prevention: Warmer window surfaces halve condensation frequency, improving indoor health.
Leading Players: YKK AP vs. LIXIL vs. SANKYO#
| Manufacturer | Model | Sound Insulation | Thermal Specs | Price (1.8 m × 1.8 m) | Notable Feature |
|---|---|---|---|---|---|
| YKK AP | Plamado U High-Grade Acoustic | T-3 (SRI 35) | Low-E insulated glass U=1.7 | ¥170k–200k | Interior swing design simplifies installs; no HOA approval required. |
| LIXIL | Inplus for Renovation Silence | T-2 (SRI 30) | Argon-filled insulated glass | ¥160k–190k | Resin frames boost airtightness; balanced sound/thermal package. |
| Sankyo Alumi | Plamake EⅡ | T-2 | Standard insulated glass | ¥140k–170k | Short-lead deliveries; expanding local contractor network. |
Product Trends#
- YKK AP introduces Acoustic Spacer options in July 2025, adding 2 dB performance below 250 Hz.
- LIXIL rolls out acoustic consulting for builders and expands touch-and-try showrooms for homeowners.
Pricing and Subsidies in Japan#
National Program: 2025 “Child & Eco Next-Gen Housing Support”#
- Incentive: ¥22,000 per window (soundproof + insulated spec), up to 20 windows per home.
- Requirements: Existing home, insulated glass, registered contractors.
- Application window: April 2025 until budget caps are reached (first-come basis).
Local Examples#
- Tokyo: Quiet Housing Program grants up to ¥600,000 for road-noise countermeasures.
- Kawasaki City: Covers one-third of costs (cap ¥300,000) for work-from-home noise-reduction upgrades.
Typical Project Budget#
- 70 m² condominium (8 windows): ¥1.2–1.5 million turnkey. Subsidies can shrink net spending to around ¥900,000.
- Standard install time: one day (≈6 hours) while occupants remain home.
Urban Condominium Case Studies#
Case 1: Along Tokyu Den-en-toshi Line (Kawasaki City, 15-year-old building)#
- Before: 48 dB in the living room near windows; 16 °C perceived surface temperature in winter.
- After: 35 dB readings; HVAC setpoint lowered 1 °C while maintaining comfort. Electricity bills dropped ¥18,000 annually.
Case 2: Near a Tokyo Music University (Nerima Ward, 20-year-old condo)#
- Household worried about piano leakage. Interior sashes plus acoustic curtains cut exterior noise by 10 dB.
- Neighbors stopped complaining; avoiding a full-scale soundproof room shortened ROI to approx. 4.2 years.
Outlook and Challenges#
Growth Forecast#
- Fuji Keizai projects Japan’s secondary window market to rise from ¥125 billion in 2024 to ¥158 billion in 2027, a 7.8% CAGR.
- Premium soundproof models (T-3+) are expected to reach 25% market share thanks to remote work and stricter urban noise policies.
Issues and Countermeasures#
Installer Shortage
YKK AP expands online training to onboard regional contractors more quickly.Condominium Rules
Promote interior-only retrofits that avoid common-area modifications; distribute HOA briefing kits.Low-Frequency Limits
Pair interior sashes with wall absorption to manage <125 Hz issues; bundle with acoustic diagnostics services.
Takeaway: Soundproof Renovation as a Value-Add Investment#
- Secondary windows boost silence, thermal comfort, and property value simultaneously—high ROI for urban households.
- National and local subsidies reduce upfront costs, accelerating adoption.
- Japanese manufacturers differentiate with sound-focused upgrades and contractor support.
For Japanese families facing traffic noise, remote workers craving quiet, or hobby musicians practicing at home, interior secondary windows remain a compelling soundproof renovation investment.