Soundproofing vs. Insulation: The Quiet Benefit
You upgraded your insulation to save money. Surprise: You can no longer hear the highway. The acoustic differences between Fiberglass, Rockwool, and Foam.
The Unexpected Perk
Most people insulate for thermal control (R-Value). But mass and air sealing also stop sound (STC - Sound Transmission Class). A well-insulated home is a quiet sanctuary.
Material Showdown
1. Fiberglass Batts (Pink Stuff)
- Thermal: R-3.5 per inch.
- Acoustic: Poor to Moderate. It is light and fluffy; sound passes through it fairly easily.
2. Mineral Wool (Rockwool / Safe'n'Sound)
- Thermal: R-4.2 per inch.
- Acoustic: Excellent. It is stone spun into fibers. It is dense and heavy.
- Use Case: Bedroom walls, Bathroom walls (privacy), and home theaters.
- Cost: 50% more than fiberglass, but worth it.
3. Spray Foam (Open Cell)
- Thermal: R-3.7 per inch.
- Acoustic: Good (stops air leakage, which carries sound).
4. Spray Foam (Closed Cell)
- Thermal: R-7 per inch.
- Acoustic: Bad. It is rigid and hard. It can actually conduct vibration like a drum skin. Do not use for soundproofing alone.
The "Air Gap" Rule
Sound travels through air. If you air-seal your windows and rim joists to stop heat loss, you also stop 80% of street noise. Triple Pane Windows: The ultimate sound blocker. The heavy glass layers and different thicknesses break sound waves.
Strategy
- Exterior Walls: Use Dense-Pack Cellulose or Rockwool.
- Interior Walls: Use Rockwool for bathrooms and bedrooms.
- Floors: Insulate between floors to stop footstep noise.
Summary
If you live near a busy road, prioritize Mass (Rockwool) and Air Sealing. The energy savings will pay for the soundproofing.
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