What is a Floating Slab?
A “floating” concrete slab is a foundation that is not anchored to deep footings or frost walls. Instead, it sits directly on the soil (grade), “floating” as the earth freezes and thaws. This is a common construction method for garages, sheds, and some residential additions, but it comes with specific moisture implications.
The Advantages
- Cost-Effective: Without the need for deep trenching and frost walls, floating slabs are cheaper and faster to pour.
- Simplicity: They are ideal for simple structures where heavy structural loads are not a factor.
The Disadvantages & Moisture Risks
- Movement: Because they move with the ground, they are susceptible to cracking if the soil settles unevenly.
- Moisture Permeability: Floating slabs often lack the rigorous vapor barriers required for commercial foundations. If you plan to finish a floating slab with vinyl or wood flooring, moisture migrating from the ground can destroy the floor covering.
IFTI’s Professional Advice
Even for a floating slab, if you intend to install high-end flooring, moisture testing is critical. Never assume a slab is dry just because it looks dry.