In a roof system, a top coat of lightweight insulating concrete is anchored to an underlying base slurry coat of lightweight concrete and a metal, gypsum, tectum or concrete roof deck by installing anchoring devices at spaced intervals. The anchoring devices may be made of plastic, steel or aluminum and include a threaded shank extending upwardly from a base plate. The anchoring devices are installed by fastening the base plates to the underlying roof deck structure or by setting the base plates in the lightweight base concrete slurry coat so that the threaded shanks of the anchoring devices extend upwardly through holes in EPS board insulation and into the subsequently applied top coat of lightweight insulating concrete. The base plate and threaded shank effectively anchor the attachment of the lightweight insulating concrete top coat to the underlying base slurry coat and roof deck to enhance resistance to wind uplift forces.