How to install a split-jamb door | Pro Construction Guide

How to install a split-jamb door

Remove strapping or anything else holding the jambs together

Remove strapping or anything else holding the jambs together, then separate them and place the jamb without the door out of the way.

Much like traditional pre-hung doors, a split-jamb door has a two-piece jamb with a tongue-and-groove joint that can be separated when you install the door in the opening.

This design allows the jamb to be cased, saving time at the jobsite and makes it easier to compensate for uneven or irregular wall thicknesses. Here are a few tips to install a split-jamb door faster than a traditional door with separate casing.

If you need to cut the jambs, you can use a hand saw or jig saw

If you need to cut the jambs to compensate for a floor that isn’t level, you can use a hand saw or jig saw to cut one or both legs and the casing. Remember: you’ll have to cut the other half of the jamb and casing to the same dimension.

A split-jamb doors is often the best choice for older homes with irregular plaster walls or odd-sized studs.

After preparing the rough opening, separate the jamb by removing any temporary hardware holding them together, typically that will be nylon strapping.

Nail the hinge side of the casing to the jack stud first

Nail the hinge side of the casing to the jack stud first while you plumb that side with a 6-foot level.

 

Many manufacturers of split-jamb doors tack the door to one jamb with a duplex nail. Remove it and insert a typical finish nail through the same hole to keep the door and casing in proper alignment during installation.

 

install a split-jamb door 4

Drive finish nails through the casing and into the jack studs and header, starting with the hinge side, then the head casing, and then the latch side. Ensure the casing is plumb and level

Check for level and trim the jambs

To install a split-jamb door, check the floor under the jambs for level. You can use a 32-inch spirit level and a graduated shim to see how much the floor is off, or you can make a level line near the header and measure down to the floor.

If the floor is out of level, cut one of the jambs a corresponding amount shorter than the other jamb. If new flooring will be installed later, raise the jambs with scraps of the flooring material to match the final floor’s height.

Install shims vertically to steady the casing.

Install shims vertically to steady the casing. Make sure you don’t nail too close to the groove in the jamb, which will obstruct the tongue on the other jamb.

Test the fit and nail the hinge side

Confirm that the hinge-side jamb can be made plumb in the opening – meaning the hinge-side jack stud is not so out-of-plumb or warped that it would interfere with installation and operation.

Place the jamb with the door installed into the opening and plumb it with a 6-foot level held along the casing leg on the hinge side. Drive 2½-inch finish nails through the casing into the jack stud. Adjust the door by leveling and nailing the head casing into the header. Plumb the latch side and fasten that casing to the other jack stud.

Use a fine-tooth hacksaw or reciprocating saw to cut through the finish nail holding the door to the jamb.

Once the first jamb is installed, slip the tongue of the other jamb into the groove

Once the first jamb is installed, slip the tongue of the other jamb into the groove  and nail the casing into the framing. The second jamb should line up just as plumb and level as the first side if installed properly.

Shim and join the jamb

Use 3-inch wide shims installed vertically to fill the space between the jamb and rough opening at nailing locations. Drive finish nails through the jamb and shims into the jack studs. Be sure you nail far enough away from the groove so it will not interfere with the tongue side of the jamb later.

Starting at the top of the door, slip the tongue of the remaining half of the jamb into the groove of the one already installed. Secure it by nailing through the stop and casing, and you’re done.

TIP

For a more rugged installation, swap out one of the short screws in each hinge for a longer one that will penetrate into the framing. Plan ahead for this, as 2½-inch #9 wood screws in the proper finish can be hard to find.

What you’ll need

  • Safety glasses
  • Hammer or nailer
  • Finishing nails
  • Level
  • Hand saw or utility knife
  • Shims
  • Door handle

 


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