Do I Need an Additional Underlayment or Vapor Barrier for Modin LVP?
Modin comes with pre-attached IXPE foam underlayment, so no additional underlayment is needed. A vapor barrier is required when installing on a concrete slab.
- Additional underlayment: Not needed
- Vapor barrier over concrete: Required
- Vapor barrier over wood subfloor: Not needed
No Additional Underlayment
Modin flooring comes with pre-attached IXPE underlayment that handles cushioning, sound dampening, and minor subfloor smoothing — no additional underlayment is needed.
- Signature, Craftsman, Herringbone: 1.5 mm IXPE, IIC 64
- Base: 1 mm IXPE, IIC 62
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Both ratings meet acoustic standards for most apartments, condos, and second-story installs.
Adding more foam underneath weakens the floor, a softer base lets planks flex under foot traffic, stressing the click-lock joints.
If your HOA requires a higher sound rating, you can add up to 1.5 mm of firm, rated acoustic underlayment (minimum IIC 50 or as required by your HOA). Avoid anything soft or spongy. This exception does not apply to Modin Herringbone — additional underlayment under Herringbone is not recommended and any issues caused by it are not covered under warranty.
Never use foam to match an adjacent floor height. Level the subfloor itself with plywood, luan, or self-leveling concrete.
Vapor Barrier Over Concrete
A vapor barrier is required any time Modin is installed over a concrete slab — on-grade, above-grade, or below-grade. It is not required over wood subfloors. Not required over wood subfloors
Modin is 100% waterproof, but it's not a moisture barrier for your home. Without one, slab moisture can migrate upward and build pressure underneath the planks.
Use a 6 mil polyethylene Vapor Barrier sheet run continuously across the slab with seams overlapped and taped.
Common Questions
Can I install over existing tile, vinyl, or laminate?
Modin can be installed over existing hard-surface flooring as long as it is flat (within 3/16" over 10 ft) and firmly attached. Never install Modin over any floating vinyl or laminate floor. See the Modin Installation Guide for full details.
Can I install over carpet?
Never install over carpet. Remove carpet and padding, both are too soft and will cause planks to flex.
Do I need a vapor barrier if my slab is sealed?
Yes. A slab sealer doesn't replace a dedicated 6 mil moisture barrier.
Do I need a vapor barrier over radiant heat?
Yes. A vapor barrier is still required over concrete with radiant heat. Keep the radiant heat system below 85°F at the floor surface, and run it for at least 48 hours before installation to drive off residual moisture.
Will extra underlayment fix an uneven subfloor?
Underlayment should never be used for the purpose of leveling out an uneven floor. Foam compresses in low spots and creates flex under load. Level the subfloor properly before laying the floors. See How Flat Does My Subfloor Need to Be?