Some of the most common configurations for bi fold doors are bottom rolling or top hung. The level of difficulty and price are among the most common concerns. There are some real pros and cons to each type as well.
With a top hung bi fold door, measurements are often an issue. The home must be specified with the right type of support to suspend a door. Improper calculations and brickwork can delay a project, so it is important to perform accurate calculations before the structural work is started.
Top hung doors are held vertical by gravity. Suspended by rollers in the upper frame, they are held in place, while tilting and instability are not a concern.
Bottom rolling bi fold doors must also be fit within the proper design parameters. If not, they can become unstable and dislodge. Panels can pop out, especially if configured in sets of three, five, or seven. This occurs with numerous configurations.
You can check for problems with bi fold doors. One is to open the first panel 90 degrees. Each foot should be on an opposing side of the bottom track that faces the direction of motion. If there’s a problem, the first panel will put too much weight on the second which can force it out of the top guide. The strain on the second panel is even more if the third panel is opened.
A captive top guide prevents this issue. Otherwise, all of the panels could come loose. The Bottom Rolling Reynaers CF77 Bi Fold Doors system is an example. The supporting beam does not take on much downward weight, which is focused on the bottom rolling rack by the design.
Top rolling mechanisms are sometimes used. The door height threshold is reduced and customers who want seamless thresholds get what they want. Flush thresholds are possible on bottom rolling systems. The downside is they don’t have weather ratings. On the other hand, you’ll get a full weather rating with a 15mm step, so that’s something to consider.