Heat and moisture resistant subfloor and optional ceiling structures made using lightweight composite panels

A subfloor of a building, comprising:

• a subfloor support structure that includes a subfloor framework comprising joists, beams, furring strips, and/or foam sheets and optionally intermediate sheathing fastened to or applied over the subfloor framework;
• and
• a plurality of lightweight composite subfloor panels fastened over the subfloor support structure to form a subfloor over which a floor finish can be applied, the lightweight composite subfloor panels each comprising:
• a foam core having a first surface and a second surface opposite the first surface;
• a first protective layer selected from a first fiber reinforced cementitious layer, thermoset polymer layer, or magnesium oxide layer formed over and covering at least a portion of the first surface of the foam core;
• and
• a second protective layer selected from a second fiber reinforced cementitious layer, thermoset polymer layer, or magnesium oxide layer formed over and covering at least a portion of the second surface of the foam core,
• wherein the lightweight composite subfloor panels are positioned so that one protective layer faces toward, and another protective layer faces away from, the subfloor support structure.

A method of constructing a subfloor and ceiling structure of a building, comprising:

• forming or providing a subfloor support structure that includes a subfloor framework comprising joists, beams, furring strips, and/or foam sheets and optionally intermediate sheathing fastened to or applied over the subfloor framework, wherein the subfloor support structure is positioned between and separates an upper floor and a lower floor;
• fastening a plurality of lightweight composite subfloor panels over the subfloor support structure to form a subfloor of the upper floor over which a floor finish can be applied;
• and
• fastening a plurality of lightweight composite ceiling panels under the subfloor framework to form a ceiling structure of the lower floor,
• the lightweight composite subfloor and ceiling panels each comprising:
• a foam core having a first surface and a second surface opposite the first surface;
• a first protective layer selected from a first fiber reinforced cementitious layer, thermoset polymer layer, or magnesium oxide layer formed over and covering at least a portion of the first surface of the foam core;
• and
• a second protective layer selected from a second fiber reinforced cementitious layer, thermoset polymer layer, or magnesium oxide layer formed over and covering at least a portion of the second surface of the foam core,
• wherein the lightweight composite subfloor panels are positioned so one protective layer faces toward, and another protective layer faces away from, the subfloor support structure,
• wherein the lightweight composite ceiling panels are positioned so one protective layer faces toward, and another protective layer faces away from, the subfloor framework.