All French doors are glass, with frames around the edge. Beyond this simple definition, interior and exterior French doors vary greatly in style, material and safety concerns. Exterior French doors let in natural light to make a room feel welcoming, bright and open; they also provide an unobstructed view of the outside. Interior French doors present a view into the next room, making both rooms appear bigger and more open, while still providing the privacy afforded by separate rooms.
French door frames are constructed from wood, fibreglass or steel. Wood is the most expensive and sought-after option, though it requires routine maintenance to keep it looking nice and new. Although wood frames work well for interior and exterior French doors, they are best for interior French door frames, which do not need the extra durability of fibreglass or steel.
Although many types of wood can be used to construct interior French doors, white oak, Spanish cedar and mahogany are popular and durable choices for exterior French doors. A fibreglass frame is a sturdy option for exterior doors because fibreglass is weather-resistant and will not warp, swell, peel or dent. Fibreglass frames are also energy-efficient and well-priced, which can save you money on your purchase and on your energy bill. Steel frames are the least-expensive, least-attractive option; although they can dent, such frames are reasonably energy-efficient, making them a good option for exterior French door frames.
Exterior French doors are made with tempered glass to protect your home from weather and intruders. Tempered glass is strong, durable and weather-resistant. The glass used in exterior French doors is also thicker than the glass used in interior French doors, though this thickness varies by door construction and style. The thinner glass used for interior French doors is not tempered, because these doors do not have to endure vicious weather. Thinner glass allows interior French doors to be constructed more inexpensively than exterior French doors.
One common misconception about French doors is that they must be double doors; there are many styles in both interior and exterior French doors. Bifold and multifold French doors are mostly used in closets and as hallway dividers, because their folds do not create a weatherproof option for exterior doors. Sliding doors are usually used as exterior applications, especially leading to a balcony or deck where there is no space to accommodate a swinging door. Inside, space-saving pocket French doors, which slide into a wall, provide easy access between rooms. Both interior and exterior French doors also come in single- or double-door styles.
Even though exterior French doors are constructed with thick, tempered glass, it is still glass and, therefore, relatively easy to break, posing a potential safety hazard. A French door could provide an easy entrance point for a criminal, because he or she only has to break the glass near the knob to be able to unlock it and get inside.
The thinner glass of interior French doors poses a safety hazard for a different reason. Children playing in a room with an interior French door could potentially fall into it and break the glass, hurting them.
Interior French doors do not require window coverings, but exterior doors often need some sort of curtain to block out excessive sunlight or offer privacy. However, covering an exterior French door eliminates many of its advantages, including the door's simple beauty. Though not the only solution, a frosted or stained glass exterior French door would provide the benefits of a curtain without the need to block the door from view.