Most people see the roof as armor—protection from rain, heat, and uplift. But in truth, the roof is also a massive, untapped acoustic surface.
Lightweight Insulating Concrete (LWIC) doesn't just deliver structural strength or R-value, it can shape how a building feels inside. In hospitals, schools, and multi-residential spaces, a quieter interior directly affects focus, recovery, and mental health. LWIC gives the roof a voice in that equation—by reducing noise, not just resisting weather.
"LWIC can improve lives through sound reduction," says Josh Lehigh, Siplast's Specialty Insulation and Cover Board Product Manager. "It's not an add-on — it's a natural extension of a reroofable, high-performance insulation system that's already doing the hard work of protecting the building."
The Unheard Sound Problem
Sound rarely takes precedence in roof design. Thermal performance? Always. Uplift resistance? Absolutely. Water management? Of course. But blocking highway noise, flight paths, or the staccato of hail? That's rarely considered.
Yet the data is clear: lower interior noise means better cognitive performance, lower stress, and improved health outcomes. The roof represents one-sixth of the building envelope and ignoring it weakens the entire acoustic strategy.
"People forget about the roof," Lehigh explains. "If you neglect the roof, sound transmission reduction will suffer."
Professionals typically contend with two broad noise pathways:
Airborne noise: traffic, aircraft, sirens, rooftop HVAC, construction, etc.
Impact noise: hail, rain, equipment vibration, and foot traffic.
Effective roof acoustics manage both, keeping unwanted sound out while controlling what leaks in or out of sensitive spaces like studios or healthcare facilities. LWIC does this inherently, without the need for complex layers or post-installation fixes.
Strength That Speaks Softly
There's a misconception that acoustic systems require compromise, and that quiet must come at the expense of strength. LWIC challenges that idea head-on.
LWIC combines mass, resilience, and thermal performance in one continuous pour. It damps vibration, absorbs impact, and creates a stable, monolithic surface that performs structurally, thermally, and acoustically—all at once.
"It's not durability versus acoustics," says Lehigh. "LWIC does both."
Siplast's systems are guaranteed to be reroofable, meaning that after decades of service, you can remove fasteners, patch with Zono-Patch®, and install a new membrane without discarding the insulation layer. That longevity reduces waste, preserves embodied carbon, and ensures consistent performance through multiple roof life cycles.
Because the insulation is encapsulated in concrete, it resists moisture, impact, and temperature swings. It's robust, renewable, and backed by an industry leading warranty against defects and installation errors—a combination rarely found in the industry.
The Physics of Quiet
The acoustic performance of LWIC comes down to science:
Porosity: The microstructure traps and diffuses airborne sound.
Mass and resilience: The concrete's density dampens vibration and lessens low-frequency transmission.
Integration: The EPS foam delivers R-value, while the concrete layers deliver mass and sound control.
"Mass is the most important part," Lehigh notes. "The more mass something has, the better it absorbs sound."
Siplast offers four proprietary mix designs—ZIC, NVS, Insulcel, and Zonocel—each calibrated for specific strength and application requirements. Together, they create solid, fire-resistant, and acoustically consistent decks that outperform layered systems relying on multiple trades or materials.
Siplast also provides a complete system (board, aggregate, and foam) under a single Roof System Guarantee rather than a patchwork of manufacturer warranties.
Proven, Measured, and Verified
Siplast has performed hundreds of acoustic tests across real roof assemblies to establish reliable STC (Sound Transmission Class) and OITC (Outdoor–Indoor Transmission Class) ratings.
Deck Type | STC Range | OITC Range |
Steel Deck | 37–56 | 34–44 |
Tectum Panels | 41–57 | 37–47 |
Structural Concrete | 51–62 | 43–46 |
Cross-Laminated Timber (CLT) | 43–60 | 37–45 |
STC measures airborne noise isolation.
OITC focuses on low-frequency, transportation noise.
Real testing, not assumptions, gives architects confidence that Siplast LWIC performs predictably across diverse deck types.
Real-World Results
Higher Education in Georgia: Keep Sound Contained
The design team initially specified multiple polyiso and gypsum layers to reach STC 55, which was effective but complex and costly. Switching to a Siplast LWIC solution simplified the build, reduced materials, and achieved the same acoustic target with a single monolithic system that can be reroofed in the future.
Healthcare: Patient-First Quiet
In hospitals, silence supports healing. A Siplast roof achieved STC 45/OITC 39, cutting external and impact noise so patients and staff could focus on recovery and care—no sound mats, no add-ons.
Multifamily Near a Highway: Everyday Peace
For residents living alongside constant traffic, Siplast LWIC improved interior sound levels to STC 47/OITC 39, transforming daily living conditions. It wasn't about a number—it was about the comfort that comes from calm.
Design with Sound from the Start
Acoustic intent shouldn't be a late-stage correction. It belongs at the concept table. Roof acoustics influence everything from wellness standards to sustainability credits.
"Siplast provides support that's specialized and complete," says Lehigh. "We're not just delivering materials—we're delivering an end-to-end design experience."
When planning for roof acoustics:
Define the outcome, not just the number. A 50 STC can mean different things, depending on the frequency range. A hospital near an airport will prioritize low-frequency attenuation while a school beneath a hail zone will focus on impact performance.
Match the system to the deck. Steel, structural concrete, CLT, and Tectum behave differently. The LWIC mix, compressive strength, and membrane attachment must adapt to the substrate.
Think long-term. Reroofable insulation, temperature moderation, and reduced landfill waste make a measurable difference not just on day one but through year 25.
Why Acoustic Comfort Is the New Standard
Acoustic design is no longer a luxury. It's a health, learning, and productivity imperative.
Quieter spaces reduce stress hormones, improve concentration, and promote wellness.
"Acoustic design can be tricky," Lehigh says. "But you don't have to go it alone."
Siplast territory managers can help design a roof assembly matched to your deck type, membrane, and local noise profile, optimizing both acoustic and thermal balance.
Key Takeaways
LWIC integrates thermal and acoustic performance without trading durability.
Tested STC/OITC ranges provide clarity for design teams.
Reroofable insulation supports sustainability and long-term ROI.
Siplast remains the only roof manufacturer that supplies board, aggregate, and foam as a single system that's backed by a Roof System Guarantee.
Quiet isn't an accessory to performance—it's part of it. With Siplast LWIC, durability, sustainability, and acoustic comfort exist in balance.
Siplast LWIC Systems are designed for strength and engineered for silence. Contact your Siplast territory manager (or reach out to acousticroofdesign@siplast.com) for a roof assembly tailored to your deck, your membrane, and your noise profile.
