Why Seattle is hard on floors
Most of the city's single-family houses sit on crawl spaces, and the Seattle area's glacial till keeps those crawl spaces damp from October through May. Many houses have daylight basements and additions on slabs. Indoor humidity swings from very dry in the heated winter months to high in summer. Every one of these facts shows up in a floating floor eventually.
How moisture reaches a floor
From below, as vapor. Water in crawl space soil and in concrete evaporates upward continuously. Without a vapor barrier, it passes through the subfloor into the back of the flooring, where laminate cores absorb it and swell, and where vinyl plank, though waterproof, can lift or trap mold underneath.
From below, as liquid. A wet crawl space saturates the subfloor from beneath; a plumbing leak does the same from above. Either swells OSB and plywood, which then pushes the floor up in ridges.
From the air. Seasonal humidity makes wood-based floors expand in summer and shrink in winter. A floor installed tight to the walls in February has nowhere to go in August and buckles.
From skipped acclimation. Boxes brought from a cold warehouse and installed the same day expand once they warm up and take on the home's moisture, pushing joints apart or buckling the field.
What it looks like
Cupping, where plank edges rise above the center. Crowning, the reverse, after a cupped floor dries. Peaking at the joints. Swollen, chalky edges on laminate. A soft or hollow area. Ridges where a subfloor seam has swelled. Gaps that open in winter. A musty smell that is strongest in spring. Any of these within the first few years is almost always a moisture or installation issue, not a product defect, which is why warranties require the installation conditions they do.
What a proper installation does
Measures first. The subfloor is metered at the measure and again after tear-out. Slabs get the test the product requires. Readings above the manufacturer's maximum stop the job until the cause is handled.
Addresses the crawl space. A damp crawl space needs a ground vapor barrier, ventilation or encapsulation and sometimes drainage. The flooring installer is not a crawl space contractor, but the measure will tell you the problem exists before you spend money on a floor over it.
Uses a vapor barrier. Underlayment with an integrated film over crawl spaces; a six-mil polyethylene sheet plus underlayment over slabs; sealed seams.
Acclimates. Product sits in the rooms at living temperature for the required period, usually 48 hours.
Leaves room to move. Expansion gaps at every wall, cabinet, pipe and doorway, sized to the product and the run length, covered by trim or transitions, never pinned by baseboard, cabinets or islands set on top.
Chooses the product for the room. Vinyl plank where moisture is a known risk; laminate where the subfloor is dry and the room is not wet.
If you already have a failing floor
Find the moisture source first. A crawl space inspection, a check of nearby plumbing and a moisture reading on the subfloor usually point to it. Fixing the floor without fixing the source produces the same failure twice. Once the source is resolved and the subfloor reads dry, the floor is replaced with the vapor barrier and gaps it should have had, and the attic stock from the original install, if any exists, helps with partial repairs.
