How Is an Interior Door Constructed Differently From an Exterior Door?

Interior and exterior doors are not the same product sold under different labels. The construction of each is different, with exterior doors given special treatment to stand up to the elements and frequent use. Interior doors are constructed to be lighter and less expensive, since they aren't subject to the same abuse as exterior doors.

Single Material

Interior doors are typically constructed of a single material, such as wood or fibreboard, while exterior doors often consist of several materials, such as wood with a reinforced metal frame. Exterior doors may be constructed entirely of steel or metal, while interior doors are rarely made from metal.

Thick and Thin

Exterior doors need to be thick and heavy enough to keep cold and heat out, as well as provide security and endure constant use. Because of this, they are typically constructed to be thicker and heavier than interior doors. The face or veneer layer is usually thicker as well.

Solid Core

High-quality interior doors have a solid core, while less expensive ones may be hollow or have a honeycomb-like structure inside. Mid-grade interior doors may have a wood fiber product in the core to mimic the heavier feel of a solid door and muffle sound. Exterior doors are solid all the way through, except for some steel doors, which may have wood or foam in the center.

Insulation Factor

Interior doors are rarely insulated, although solid ones may provide some insulation against drafts. Exterior doors may be constructed with insulation to help control energy costs. The foam core in steel doors, for example, serves as insulation against summer heat and winter cold.

Outer Appearance

Both interior and exterior doors frequently feature raised panels, either real or simulated, as face decorations. Exterior doors are sometimes constructed with decorative panels on only one side, while interior doors are usually the same on both sides. Exterior doors commonly use large panels of frosted glass as decorative elements, while glass is not common in interior doors, except for French-style doors.