What is the difference between jamb depth and throat size?
Jamb depth is the total width of the frame profile from face to face, including the returns that wrap over the wall surface. Throat size is the inside measurement between the returns, which equals the wall thickness. On a drywall wrap-around frame, the jamb depth is always 1 inch greater than the throat size.
How do I calculate jamb depth from wall thickness?
Add 1 inch to the wall thickness. For example, a 4-5/8” wall requires a frame with a 5-5/8” jamb depth. The extra inch accounts for the two ½-inch returns that wrap over the drywall on each side of the wall.
What is the most common jamb depth for commercial door frames?
The two most common jamb depths are 5-5/8” and 5-7/8”. A 5-5/8” jamb depth fits a 4-5/8” wall (typical 2x4 wood stud or 3-5/8” metal stud with 1/2” drywall on each side). A 5-7/8” jamb depth fits a 4-7/8” wall (the same stud types with 5/8” drywall on each side).
What happens if I order the wrong jamb depth?
A frame with the wrong jamb depth will not sit flush against both sides of the wall. If the jamb depth is too small, the returns will not reach the wall surface, leaving gaps. If the jamb depth is too large, the returns will protrude past the wall. Either condition prevents proper installation and may void fire ratings on rated assemblies. Measuring the wall thickness before ordering is the single most effective way to avoid this problem.
Does jamb depth change for fire-rated frames?
No. The jamb depth formula (wall thickness + 1 inch) is the same for both fire-rated and non-rated drywall wrap-around frames. Fire-rated frames at 20-minute, 45-minute, 60-minute, and 90-minute levels all follow the same calculation. However, assemblies requiring a 3-hour (180-minute) rating must use masonry frames, which have different depth requirements.
Can I use an adjustable frame if I am unsure of the wall thickness?
Yes. Adjustable throat frames feature a split jamb design that accommodates a range of wall thicknesses. They are useful when wall thickness is unknown at the time of ordering or varies across multiple openings. Adjustable frames are typically more expensive and may not be available in all fire-rated configurations. Contact CDF to confirm availability.
Where do I measure wall thickness for a door frame?
Measure at the rough opening where the frame will be installed. Place a tape measure across the edge of the wall from finished surface to finished surface. Take measurements at the top, middle, and bottom of the opening. Include all finish layers (drywall, plaster, tile backer board). If measurements vary, use the largest measurement.
What wall thickness does a 4-5/8 inch throat size accommodate?
A 4-5/8” throat size accommodates a 4-5/8” wall. This is one of the most common wall thicknesses in commercial construction, corresponding to a 2x4 wood stud with 1/2” drywall on each side, or a 3-5/8” metal stud with 1/2” drywall on each side. The corresponding jamb depth for this throat size is 5-5/8”.