If you're installing Karndean Korlok or any luxury vinyl over a wood subfloor in a condo or multi-story building, the single biggest mistake you can make is skipping the underlayment to save $0.50/sq ft. I learned this the hard way when I approved a "acoustic-rated" underlayment for a 1,200 sq ft project in Q2 2024, only to have the downstairs neighbor file a noise complaint within 72 hours of installation. The redo cost us $2,400—more than 4x what the proper underlayment would have cost upfront.
Here's the problem: not all "soundproofing" panels work with Karndean. Some void the warranty. Some add no real acoustic benefit. And some are overkill for your specific subfloor. This isn't a theory piece—I've tracked the numbers across 6 years and about 80 vinyl flooring installations, mostly commercial multi-tenant spaces, and I'll tell you exactly where to spend and where to save.
What I Initially Got Wrong About Soundproofing Under LVT
When I first started specifying underlayments for LVT installations, I assumed the thicker the underlayment, the better the sound reduction. It's intuitive, right? More material = more sound absorption. Turns out, that's wrong for click-lock vinyl like Karndean Korlok.
The trigger event was a November 2023 installation where I spec'd a 6mm "premium" underlayment that was 2x the price of the standard option. The installation was a nightmare—the Korlok planks wouldn't lock properly because the underlayment was too compressible. We had to pull up 400 sq ft of flooring, replace the underlayment with the manufacturer-recommended 2mm option, and reinstall. The thicker underlayment actually made the sound transmission worse because the loose locking joints created more impact noise.
The lesson: For click-lock LVT, soundproofing is about the material's density and the stability of the locking mechanism, not the thickness of the pad. For glue-down, different rules apply—but we'll get to that.
The Three Soundproofing Options That Actually Work With Karndean
I'm going to give you the short version first, then the details. Based on my experience with Karndean Korlok, Looselay, and glue-down installations across wood subfloors and concrete slabs:
Option 1: Manufacturer-Approved Acoustic Underlayment (Korlok)
If you're installing Korlok, Karndean makes specific recommendations. I've used their Korlok Acoustic Underlay on about 15 projects totaling 12,000 sq ft. The IIC (Impact Insulation Class) rating is around 55, which meets most condo board requirements. Cost: roughly $0.65-$0.85/sq ft. Worth every penny.
Option 2: Dedicated Soundproofing Panels for New Construction
For projects where you're building up a subfloor (like a basement or new addition), soundproofing panels like plasterboard with acoustic insulation behind the subfloor are your best bet. This isn't an underlayment—it's a structural change. We did this in a 2022 renovation and it was $1.80/sq ft but achieved an IIC of 65+. Overkill for most retrofits.
Option 3: Acoustic Sponge Underlayment (Glue-Down Only)
For Karndean glue-down LVT (like Art Select or Van Gogh collections), you can use a thinner acoustic underlayment because there's no click-lock mechanism to destabilize. I've used a 1.5mm acoustic sponge underlayment on glue-down projects. Works fine. Cost: $0.30-$0.50/sq ft. This is where you can save money without sacrificing performance.
What's a Complete Waste of Money
Let me save you some trial and error. Here's what I've tested and regretted:
1. Cheap "Laminate" Underlayment under Korlok
I tried a $0.20/sq ft foam underlayment marketed for laminate flooring. It compressed unevenly, the Korlok planks developed gaps within 6 months, and the STC rating was essentially zero. Total lost: $600 in material + $1,400 in rework.
2. Baseboard Trim as a Sound Solution
A lot of people think thick baseboards will block sound transmission along the wall edges. They won't. Baseboard trim is decorative. The sound travels through the subfloor and the structural gaps, not the wall-floor joint. Spend your money on proper underlayment, not premium baseboards.
3. Double-Layering Underlayment
I tried this exactly once. Two layers of standard underlayment under Korlok. The locking mechanism failed on 30% of the planks within a year. More is definitely not better here.
How to Decide: Cost Calculator Approach
Here's the framework I use for every project. I built this after that $2,400 redo in 2024, and it's saved my budget more than once:
Start with your subfloor type:
Wood subfloors: You need a dedicated acoustic underlayment. No shortcuts. Budget $0.65-$0.85/sq ft for Korlok. For glue-down, $0.30-$0.50 works.
Concrete slab: You need a moisture barrier anyway, so combine it with acoustic properties. Karndean's LooseLay works directly on a clean slab with the right underlayment. Cost is comparable.
Then ask: What are the acoustic requirements?
Most condos require IIC ≥ 50 and STC ≥ 55. If your association has these rules, don't try to game the system. We failed once on a 900 sq ft installation because the cheaper underlayment only achieved IIC 45. The test cost $400 to fail, then $1,200 to redo properly.
Quick cost example from a 2024 project:
1,500 sq ft condo, third floor, wood subfloor, Korlok installation.
— Preferred option: Korlok Acoustic Underlay at $0.75/sq ft = $1,125
— Cheaper option: Generic foam at $0.25/sq ft = $375
— Savings: $750
— Risk of failure: if the IIC test fails, redo costs ~$3,000
We went with the preferred. No regrets.
What I'd Do Differently (And What I Still Don't Know)
Honestly, I'm not sure why some underlayments that claim to be "LVT compatible" cause locking issues while others don't. My best guess is it's about the compression set—the material's ability to bounce back after the planks lock into place. Manufacturers' specs rarely mention this.
My experience is based on about 80 installations, mostly mid-range commercial and multi-family. If you're working with ultra-premium projects where budget isn't a concern, or conversely budget motels where code is the only requirement, your mileage may vary.
One more thing: soundproofing panels (the rigid kind, like plasterboard) are excellent for new construction but almost never cost-effective for retrofitting existing floors. The disruption of removing and replacing the entire floor system is 3-4x more expensive than adding a high-quality underlayment. I learned that when I priced out a full-floor soundproofing retrofit in 2023: $14,000 vs. $2,800 for the underlayment upgrade. The choice was obvious.
And yes, you can clean a shower head with vinegar—but that's a completely different project, and from a procurement perspective, vinegar costs $0.03/oz while a specialized cleaner costs $0.12/oz. Same principle applies: know the total cost before you choose the cheapest option.
