Our basement slab feels cool and slightly damp — should we install a vapour barrier under vinyl?

Yes, you should definitely install a vapour barrier under vinyl flooring on a basement concrete slab, especially with the cool and damp conditions you're describing. This is critical for preventing moisture issues that can damage your flooring and create mold problems.

Moisture vapor transmission is a major concern with concrete slabs, particularly in basements where hydrostatic pressure and temperature differences create ongoing moisture movement. Even concrete that feels only "slightly damp" can transmit enough moisture vapor to cause vinyl flooring to fail, develop mold underneath, or create adhesive problems. The cool temperature you're feeling often indicates moisture evaporation, which means water vapor is actively moving through the slab.

For basement vinyl installations in Ottawa, a 6-mil polyethylene vapor barrier is the minimum requirement, but many contractors prefer epoxy moisture sealers or specialized subfloor systems like Barricade or similar products that combine vapor protection with thermal insulation. These systems not only block moisture but also provide a warmer, more comfortable surface temperature. The vapor barrier must extend up the walls about 3 inches and be properly sealed at all seams and penetrations.

Proper moisture testing should be done before installation using calcium chloride tests or relative humidity probes to measure the actual moisture vapor emission rate. Ontario's climate with freeze-thaw cycles can create additional moisture pressure on basement slabs. Most quality vinyl manufacturers will void warranties if proper moisture mitigation isn't installed on concrete substrates.

Before proceeding with any flooring installation, have the slab properly assessed and ensure adequate vapor protection is installed. For a comprehensive moisture evaluation and professional basement flooring installation, request a quote from Ottawa Floor Install to ensure your project meets all moisture protection requirements.