How to Install Exterior Prehung Doors

Things You'll Need

2½,-inch plated deck screws

Instructions

Check the opening with a builder's level to confirm that both sides are plumb, and then measure horizontally between the two sides at the top, middle point and bottom to ensure the sides are parallel. Check the faces of the trimmers (the two wall studs on each side of the opening) with a square to ensure they are square to the adjacent wall surface.

If the trimmers are not plumb or square, use a pry bar to adjust the trimmer by moving it in or out at the top or bottom until plumb. Insert shims as needed to fill any gap between the trimmer and the wall stud behind it, then nail through trimmer and shims to secure in place.

Place a builder's level on the floor of the opening. If either side of the opening is lower than the other side, slide shims under the straightedge to adjust it until the level's bubble is centered. Always use two shims, one from each side, to keep the perpendicular surface level as well. Add shims at the center point of the opening to fill any gap that remains. Secure these shims in place with 8d finish nails. These will ensure the door sill will be supported as level.

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