"Understanding Your Home" by Building Inspector Mark Visser
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Pre hung doors

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Pre hung doors

Pre-hung Doors

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What is a Pre-Hung Door?

A pre hung door is, as the name implies, a door that comes hinged into the door frame. This means that the most tricky parts of hanging a door have been done for you. The door jamb has been mortised so all hinges are correctly spaced and installed. Without proper spacing and placement of the hinges the door may bind against the doorstop or is not flush with the door jambs when in closed position. Also pre-hung doors have pre-drilled holes for the door lock or door handles and is mortised to accommodate the latch bold and striker plate. The door stops have been installed as well.
Pre-hung exterior doors come also with an installed threshold and magnetic weatherstripping. A pre-hung door speeds up installation because all we have to do is place it in the wall opening and secure it to the wall right? Not quite so. The door and jamb must still be carefully adjusted, with shims, so the door sits level and plumb into the wall opening.
It is also crucial to know the thickness of the wall finish. I always nailed a few strips of drywall around the framed stud opening and used that as a guide to install the door jamb flush with the drywall.
A fair bit of skill is required to shim the door jamb so the door hangs well. If the hinged side of the door jamb is not installed perfectly plumb the door will not stay put in any position but will either close or open on it's own. The doors come primed and are either flat or have a ready to paint textured wood grain surface. All interior hollow-core doors are 1 3/8" (33 mm) thick.
Shim tips
You have a choice of nailing the frame through the shims or right next to it. I always preferred to nail through the shims for the following reasons:
1. If necessary the shims can be still adjusted by prying the jamb away from the framing.
2. It prevents the shims from sliding down.
3. The shims will not move on me when I trim them to length.
Rough Stud Opening (RSO) for pre-hung interior doors: Two inches (50 mm) wider than the door itself and two inches (50 mm) higher than the actual door. Most interior doors are 6'8" high (80") so the height for the RSO would be 82".
Super fast install pre-hung door kits.
NO SHIMMING. Install a door, door jambs and trim in 15 minutes!

This kit comes with a door, two jams and header. Doorstops, trim (casing), hinges and holes for door handle are factory installed. The jamb and attached trim slide like a sleeve around the wall and is held in place by nailing through the trim. That is it! No shims required and no nailing through the jambs.

Pre-hung door on dispay at a
builders supply store

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