In retrofit situations, you do not usually have the luxury of removing a door to measure the opening precisely and leaving the opening empty while waiting for the door to arrive. Typically, the homeowners want to keep their exterior door in place during the ordering process.
For this reason, it is important to measure carefully for door replacements.
Begin the journey with the sizing chart at ProVia.com, which can help you determine if the door you need is a standard size or a custom size. The dimensions used on the chart are explained below and in the video above.
Rabbet to rabbet opening size:
The dimension inside the pocket of the jamb. Measure the top, bottom, and middle, and use the smallest number to plug into the chart.
For height, measure between the inside of the head jamb and where the threshold will sit in the opening.
Determining where the threshold will sit may be difficult because there are several floor configurations that you may encounter.
The project in this video has a solid oak threshold, which means extrapolating around the threshold.
The point is to measure to the top of the subfloor (accounting for floor coverings).
Next, subtract the appropriate amount to allow room for the new threshold (1-1/4 inch for ProVia doors) and any extra clearance you'll need for floor coverings, such as a throw rug.
If entering the doorway from the outside includes a step up, then consider how much rise you are adding to the step. You may need to adjust the outside step or reconsider the subfloor elevation if the home is for an older adult, or if the step exceeds your local code.
Also, consider the top of the door. Raising the door a little to account for floor coverings may allow you to use a standard size door, but a header, lintel, or brick may obstruct movement.
Getting the correct height is very important in retrofit situations because there is less wiggle room than new construction situations.
The size of the door and jamb assembly. It is the outside measurement of the jambs, side-to-side, and the threshold-to-head jamb up and down.
Rabbet to rabbet size is the easiest way to get to the actual unit size. Because measuring the existing door frame requires removing door casing and digging into the wall a little bit.
Rough opening is the space between the inner studs and between the subfloor and the door header. The rough opening size is not used much in remodeling; instead, unit size is the standard dimension.
Wall thickness. Distance between exterior trim and interior trim. Jamb depth should not be the exact number because the walls are in all likelihood, not flat, plumb, or straight.
You should usually add at least 1/16 inch to whatever you measure. This extra depth helps to make sure that the interior trim sits flat and tight against the jambs.
Wider jamb depth is also helpful when replacing doors in brick walls because they can help cover the caulk line left from the previous installation. Installers typically like to add 1/4 - 3/8 inch to the jamb depth for covering the caulk line.
Brickmold to brickmold size
From outside of exterior trim to outside of exterior trim. You do not necessarily need always to use brickmold; it's just what we call it.
This measurement is not for ordering doors by; it is a measurement for exterior trim only. With these numbers, ProVia can send the proper precut trim for a fast and clean trim install at the jobsite.
Measuring brickmold to brickmold in J-channel
Outside of trim to outside of trim, in between the j-channels. Measure the height from the top of the trim to where the threshold will sit below.
If you are ordering a cladding system for the trim, make sure to subtract enough space for the cladding to fit. You are in charge of the cutbacks.
The sizing document will give you the standard sizes. The definitions in this video and on this page will help you determine which door you need. This information also applies to French doors and door/sidelight units.