Accessory Dwelling Units (ADUs) are booming in California as homeowners look to maximize their space. Many are choosing to convert garages into living spaces, whether for rental income, guest quarters, or extended family. One of the most popular flooring choices for ADUs is luxury vinyl plank (LVP) or laminate flooring—both offering durability, style, and affordability. However, installing these floors over an existing garage concrete slab comes with challenges. Here’s what you need to know before making the transition.
The Biggest Concern: No Vapor Barrier Under Garage Slabs
Unlike traditional home foundations, garage slabs were often poured without a vapor barrier (plastic sheeting) underneath. This can lead to moisture issues, especially when installing floating floors like LVP or laminate. Without proper preparation, trapped moisture can cause:
• Warping and Buckling – Planks may expand or lift.
• Mold and Mildew Growth – Excess moisture can lead to unhealthy conditions.
• Adhesion Issues – If glue-down LVP is used, moisture can break down adhesives.
How to Address Moisture Issues
Before installing any flooring, the garage slab must be sealed properly to prevent moisture from seeping through. Here’s the process:
1. Moisture Testing – Use a moisture meter to check the humidity levels of the slab. Acceptable levels should be below 4% for most flooring manufacturers’ requirements.
2. Applying a Concrete Sealer – A high-quality moisture barrier sealer should be rolled onto the concrete. This helps block moisture from rising.
3. Using a Vapor Barrier Underlayment – If installing floating LVP or laminate, a 6-mil plastic vapor barrier or specialized underlayment should be used for added protection.
Leveling and Grinding: Dealing with an Uneven Slab
Most garage floors are not perfectly level because they were originally designed to slope for drainage. Installing floating floors over an uneven slab can lead to:
• Gaps Between Planks – Floors won’t lock properly.
• Soft Spots or Hollow Sounds – Floating floors need a level base to perform correctly.
• Premature Wear – Planks under stress will fail over time.
Steps to Fix an Uneven Garage Slab
1. Grinding High Spots – Using a concrete grinder to smooth out raised areas.
2. Filling Low Spots – Apply self-leveling compound where needed.
3. Checking for Cracks – Any cracks should be filled with a polyurethane concrete patch before sealing.
Choosing the Right Flooring for a Garage ADU
Once the slab is properly prepped, choosing the right flooring is key.
• Luxury Vinyl Plank (LVP) – Best for moisture resistance, durability, and ease of installation. Can be installed as floating or glue-down.
• Laminate Flooring – Provides a realistic wood look but is less water-resistant than LVP. Must be installed with a moisture barrier.
• Engineered Hardwood – A premium choice but requires a fully level and sealed slab.
Final Thoughts
Garage ADU conversions are a great way to add living space, but flooring installation over an old concrete slab requires proper preparation. Without sealing, leveling, and moisture control, the new floors can quickly fail. By following these steps, homeowners can ensure their ADU flooring stays durable, beautiful, and problem-free for years to come.
Need help selecting or installing the right flooring for your ADU? Contact Perry Floors today for expert advice and installation!
