Abstract: Disclosed is a composite wood structure including (a) first and second spaced layers, and (b) a core interposed between the layers. A sheet-like vapor barrier is between the layers and limits migration of moisture through the barrier to less than about 6 grams per square meter of barrier area per hour. The wood structure is thereby made warp-resistant. In another embodiment, the structure has a vapor barrier on an outer surface and may have one or more additional vapor barriers between structure layers. Preferred vapor barrier materials include melamine formaldehyde impregnated paper, phenol formaldehyde impregnated paper, thermoset materials, thermoplastic materials and aluminum foil.