Folding glass walls or bi-folding exterior glass doors are used to create large openings in a building that can be fully opened to physically join the outside with the inside. This is why people are attracted to them in increasing numbers. Imagine having a kitchen or great room where you can hold a party that allows a free flow to your terrace or patio area as though it is simply an extension of the indoors. This notion excites folks, and every bi-folding door serves the same function. It is hard to create differentiation between them but buying the least expensive one might not be the best choice for you.
Most bi-folding doors are top hung. This means that the trolley or roller systems that support the weight of the movable sashes are suspended from tracks in the head of the door frame. The reason for this is that roller assemblies are bulky and susceptible to excessive wear and premature failure when located within the sill of the door where water and dirt can easily accumulate. The downside of top hung doors of large widths is that the header of the opening needs to be able to support the weight of the door that is generally about 50-75 pounds per running foot of width without sagging. In new construction, architects and engineers can calculate this into the building design to make sure that there won’t be problems down the road. Those retrofitting bi-folding doors need to pay special attention to the existing header design to make sure it can carry the load. Sliding doors, on the other hand, almost always have bottom rollers and avoid this header load consideration.
The manufacturers distinguish themselves from one another with materials used for the framing and sash systems. Profiles made from wood, steel, aluminum, thermally broken aluminum, aluminum clad wood, vinyl and vinyl-clad wood options are out there, and they are all about the same except for surface finish and durability. Metal frames are stronger and can be made thinner, but they are generally not as good at insulating you from temperature differences between the inside and outside. Wood and vinyl frames are better insulators, but generally not as strong as metal ones.
Visually, if the profiles are painted, paint is paint and nobody cares. Vinyl and aluminum require factory painting and the colors offered are usually not so plentiful. Wood frames offer changes in species and stain options and are perceived to be aesthetically more pleasing especially when viewing them from the inside. The downside of wood is that it does not weather as well as metal and plastic profiles. Swelling, rotting, and general surface deterioration and maintenance costs deter people from wanting wood surfaces on the outside. Metal and plastic clad wood solve the exterior surface problem.
Bi-folding, mostly glass, exterior doors almost always use insulated glass but not all manufacturers offer a full range of glass options. The exact location and climate of the installation need to be considered to make sure that thermal insulation and solar heat gain are optimized. The sun is a blessing in cold climates and a problem in southern sunny ones.
Finally, don’t forget that for most of their lives, bi-folding doors are closed. What they look like in this position is how you will view the outdoors the most often. The visual width or thickness of the frame panels where the moving panels come together need to be considered. Not all doors are created equally. Most bi-fold doors have glass-to-glass dimensions in the range of 7-8 inches. 2Fold™ doors have been designed to have this face dimension at only 2-3/16” which is really, really thin. This allows 35% more light and gives you 35% more view to the exterior than any other folding door system while NOT sacrificing either strength or thermal insulating value. Learn more about this exciting alternative at www.2folddoors.com.