If you’re working on a residential construction project, then here’s a handy guide to assist you figure out the size of interior door rough opening on the exterior wall. To begin, measure the opening with a tape measure or the simple pencil and paper method. Next, measure the height of the doorway at the top and bottom.
This is important because if you can cut a piece of wood that is the same height as your door (the “cut height”), then you’ve got all the necessary skills to successfully frame rough openings for interior doors. Just add 14 inches to that measurement.
Now let’s discuss what is the rough opening for a 32-inch door. For this example we will assume that the interior door rough opening is a bifold door, and that it is a “wide door.” Some other examples of wide doors would be sliding patio doors, and accordion doors. In fact, there are so many variations on what is the rough opening for a door, that there are literally hundreds of articles written about it!
Here are the measurements you will need. Write down the bottom step of the door, measured in inches, and write down the top step, measured in inches. For this example, we’ll use a bifold door, so we measure from the bottom of the door, to the top of the fold line, and then to the bottom of the doorway, again measured in inches.
Then we multiply both the bottom and top measurements to get the actual rough opening – exactly what is the height of the door at the very center point, just outside the doorway. Once you have these numbers, find the NACH (National Average for Hardie Thickness) value for the door you are trying to qualify.
This number is used as a standard for determining the rough openings for every type of door you can imagine. In our example, it would be: NACH =.8125, or about two and a half inches. If this number is too high, then don’t even bother with the door – it won’t even close! If the number is too low, then your exterior door might be too flimsy.
Another important factor you must consider when choosing an exterior door is the actual ID of the door. The ID is measured in inches and generally considered the height of the door itself. The higher this number is, the sturdier it will be when closed. In other words, if the opening is more than six inches high, then it just doesn’t make sense to invest in a heavy door.
To choose which doors meet your unique set of requirements for rough openings, you will need to measure the actual rough openings for each style and design, as well as the actual ID of the door. Most manufacturers will provide a complete set of measurements for their doors along with the corresponding industry standard ID.
All you will need to do then is take these numbers and multiply them to come up with your unique set of dimensions. Remember that this ID number changes over time, so the official government set of measurements for your door may no longer be the most effective for your home.
If your door is only six inches high, then your rough opening dimensions will be different from those for double-walled, sliding patio doors, and even sectional doors. For those types of doors, you may need to add on another three inches to the rough opening measurements to compensate for the additional space required for a door frame.
For example, if your door has a two inch frame, then it will be three inches deep instead of two. This extra depth will help keep water from getting inside your home or between rooms, thus increasing the life of your doors.
Some home builders will tell you to always use exterior doors with rough opening dimensions that are at least six inches deep, regardless of the interior door you use. If your home was built using sliding patio doors or siding, then these professionals will know the best way to ensure you get the most out of your home.
If your home was built using bifold doors, then these pros can also give you the most efficient use of your property. Regardless of whether you use interior doors, sliding doors, or a combination of both, it’s important that you have the rough opening specifications in place so that you know how much space you are opening your home into.