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Sizing a Rough Door Opening for Installing a Prehung Door

Tips on How to Size a Rough Door Opening for Installing a Prehung Door

By Mark J. Donovan

When installing a prehung door into a wall it is important to first size the rough door opening. If the sizing on the rough door opening is too small or large, installing the prehung door will be impossible. The prehung door will not fit into it, and if it is too large there will be wide gaps that will make it difficult for the prehung door to be installed properly.

Typically the rough opening required when installing a prehung door should be sized 2 inches wider and 2 inches higher than the prehung door itself. For example a two-foot, eight inch (32”) by six feet, eight inch high (80”) prehung door, would require a rough opening width of 34 inches and a height of 82 inches.

Sizing Rough Door Opening for Installing Prehung Door

Sizing Rough Door Opening

Sizing the rough opening correctly will allow for the prehung door doorframe casing to be installed with about 1 inch of play on both sides, and 1 inch on both top and bottom. This spare space will allow the prehung doorframe to be installed correctly. The prehung door will be able to be leveled and plumbed so that the door swings freely.

Installing Prehung Door

Note that when installing the prehung doorframe shims and blocking should be used at both the hinge and door lock locations. The shims and blocking should be wedged in between the prehung doorframe and the wall studs that form the rough opening.

When securing and installing the prehung doorframe to the studs, nails should penetrate through the shims/blocking material. This will help to prevent flexing of the prehung doorframe when it is opened and closed.

Note on Sizing Rough Door Openings

Note that these guidelines are typical framing standards that are employed in the home construction business. You should always check with the prehung door manufacturer or product specifications to confirm the rough opening requirements for your particular prehung door.

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