Door types
Every door in a home falls into one of two categories: interior or exterior. The distinction matters more than it might seem — the two types are built differently, rated differently, and chosen for different reasons. Using the wrong one for a given application is a common and avoidable mistake.
Interior doors
Interior doors separate rooms within the conditioned envelope of the home. Because they aren't exposed to weather, they can be built lighter and with less concern for insulation or moisture resistance.
Most interior doors are hollow-core — a thin wood or composite skin over a cardboard honeycomb frame. They're inexpensive, lightweight, and easy to hang, which makes them the default choice for bedrooms, closets, and hallways. Their main limitations are sound transmission and durability; a hollow-core door offers little acoustic separation and won't hold up well to hard use.
Solid-core interior doors use a composite or wood-block fill instead of a honeycomb. They're heavier, quieter, and more resistant to damage. They're a common upgrade for home offices, laundry rooms, or any space where sound control matters.
Common interior applications
| Location | Typical choice | Notes |
|---|---|---|
| Bedroom | Hollow-core | Privacy latch sufficient |
| Bathroom | Hollow-core | Consider solid-core for shared walls |
| Home office | Solid-core | Sound reduction is the main driver |
| Closet | Hollow-core, bifold, or sliding | Full-height preferred for reach-ins |
| Laundry room | Solid-core | Noise and moisture considerations |
| Garage entry | See exterior doors | Fire rating may be required |
Exterior doors
Exterior doors form part of the building envelope. They're exposed to weather, temperature swings, and potential forced entry, so they're built to a substantially higher standard than interior doors.
A typical exterior door is at least 1¾ inches thick (compared to 1⅜ inches for interior), solid or foam-filled throughout, and fitted with weatherstripping on all four sides. Insulation value (expressed as an R-value or U-factor), structural rigidity, and security are the primary selection criteria — aesthetics come after those are satisfied.
Exterior door requirements
A well-chosen exterior door should:
- Resist air and water infiltration
- Provide meaningful thermal insulation
- Accept a deadbolt without compromising structural integrity
- Remain stable across seasonal humidity and temperature changes
Wood exterior doors can warp or swell if not properly finished and maintained. Fiberglass and steel doors avoid this problem and tend to outperform wood on insulation and security, at the cost of some aesthetic flexibility.
Garage entry doors
The door between an attached garage and the living space is an exterior door in function even though it's interior in location. Most building codes require it to be fire-rated — typically a 20-minute rated solid-core door, though local requirements vary. Always verify before selecting a door for this opening.
When in doubt about whether a location calls for an interior or exterior door, ask: is this opening part of the building's thermal and weather barrier? If yes, treat it as exterior.
Next: Materials
The interior/exterior distinction shapes which materials make sense. Door materials covers the full range — from hollow-core to steel — and when to choose each.