Installing a prehung door may seem straightforward, but getting it right requires precision. There are four key rules to follow for a proper fit. The door must be level so it sits evenly, plumb so it stands perfectly vertical, and square so all corners form precise 90-degree angles.
Finally, it must be true, meaning every surface should pass multiple level checks to ensure a flawless installation. If any of these elements are not aligned correctly, the door won’t function properly.
Installing a prehung exterior door is one of the easiest door installation projects you can tackle. This type of door comes attached to its own frame, making installation more straightforward. Keep reading for a step-by-step guide on how to do it.
| Project difficulty: Intermediate to Expert Estimated time to complete: 3 to 5 hours Project cost: $ 657 |
I asked Christopher Gaetzke, the owner of Steadfast Handyman in Menomonie, Wisconsin, whether installing a prehung exterior door is a DIY-friendly project or best left to a professional.
He responded, “Installing a replacement pre-hung exterior door can be a DIY project if you have two people and moderate DIY experience. You need to plan for hang-ups like a rotted threshold or sheathing. The rough opening size may end up different than expected.”
When asked about common mistakes DIYers make during installation, Gaetzke said, “Some mistakes would be not having all of your materials ready to put the new door back in like flashing tape, spray foam insulation, caulking, multiple sized screws, shims and possible new interior or exterior trim to fit to existing siding or interior trim.
“Another possible mistake would be not measuring door dimensions, especially the depth of the threshold, which can vary from 4 9/16″ to 10″. If you get a door that is not deep enough, then you have to make custom jamb extensions.”
Supplies Needed
Materials:
- Prehung Exterior Door
- Screws
- Shims
- Sill Pan
- Exterior-grade Caulk or Sealant
- Blanket Insulation
- Lockset and Deadbolt
- Interior and Exterior Trim
Tools:
- Measuring Tape
- Level
- Utility Knife
- Hammer
- Drill and Drill Bits
- Caulking Gun
- Counter Sink Bit
How to Prepare for Exterior Door Installation
Before installing the new door, you must take important steps like measuring the doorway and removing the old one if you are replacing it. These steps ensure a proper fit and a smooth installation process.
Check and Measure the Door Opening
To ensure a proper fit, you must take accurate measurements before installing a new exterior door. Start by measuring the existing door’s width and height, rounding up to the nearest inch for reference. Next, remove the interior trim and measure the door frame from stud to stud, confirming both width and height.
Manufacturers typically make standard doors 36 inches wide and 80 inches tall, but you should verify your specific dimensions. Also, check the jamb depth by measuring the thickness of the wall to ensure the new door sits flush.
Choose a new door that is about ¾ inch narrower and ½ inch shorter than the opening to allow for adjustments. Additionally, measure the exterior opening by checking the outermost edges of the door frame, ensuring it aligns with your home’s structure.
Double-check all measurements to guarantee a precise fit. A door that is too large won’t fit, while one that is too small can leave gaps that affect insulation and security. With the right measurements, you can confidently choose a pre-hung door that installs smoothly.
Remove the Old Door and Frame
Before installing a new door, you need to remove the old one carefully. Start by detaching the door from its hinges and lifting it out of the frame. Then, pry off the interior and exterior trim to expose the door frame. Learn how to take a door off its hinges to make the replacement process easier and prevent damage to the frame.
Use a pry bar or oscillating tool to loosen and remove the frame, taking care not to damage the surrounding walls. Once you remove the frame, clean up the rough opening and check whether the framing is level and in good condition. A clear and properly prepared opening will ensure a smooth installation of the new door.
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Step 1: Prepare the Rough Opening
Steps to Replace a Prehung Exterior Door
The crucial step in preparing the rough opening for door installation is to ensure that the subfloor is level and that the opening is square and plumb. Start by placing a level along the floor and across the door frame to check for any uneven areas.
If the opening is slightly out of square, use shims to adjust it by inserting them behind the jamb where needed. Secure the shims with screws, but ensure they do not interfere with the new door’s fit.
Install the Sill Pan
Installing a sill pan is a key step in preparing the rough opening for a door, as it helps protect the sill from water infiltration and prevents potential water damage.
First, position the corner pieces on the sill, then place the middle section on top. If the middle piece is too wide, trim the ends with a hacksaw for a proper fit. Once aligned, apply PVC cement where the middle piece overlaps the corners, pressing it firmly into place. Hold the pieces together briefly to allow the cement to bond securely.
Next, remove the sill pan and apply three beads of caulk to the rough opening before setting it back in place and pressing it down. Finally, seal the seams, edges, and back of the sill pan to ensure a watertight seal.
Step 2: Put the Door in Place
Start by applying a continuous bead of sealant along the back of the brick mold, which is the exterior trim attached to the door frame. This helps create a weatherproof seal between the door and the house, preventing moisture from seeping in.
Next, carefully lift the prehung door and place the bottom edge onto the sill. Make sure to center it and press it flush against the opening. Then, slowly tilt the top of the door forward until it fits snugly into place within the rough opening. Ensure the frame is aligned evenly with the wall before proceeding to secure it in position.
Step 3: Shim and Level the Door
Use shims to keep the prehung door square and properly aligned in the frame. Place shims above each hinge at the top, middle, and bottom, as well as behind the strike plate on the latch side.
To install them, drill pilot holes near the hinges and the strike plate using a countersink bit. Partially drive screws into the middle holes to hold the door in place while you make adjustments. Use a level to check if the hinge side is straight, both inside the frame and along the outer edge.
If everything is aligned, secure the door by partially driving screws into the top and bottom. Place shims behind the strike plate for added support.
Step 4: Secure the Door’s Hinge Side
From inside the house, check that you have centered the door frame within the rough opening and that it stays plumb. Use a level to ensure it is straight. Next, drill pilot holes through the hinges and insert screws partway to temporarily hold the frame in place.
To provide extra support, slide shims behind each screw location on the hinge side. These shims help keep the frame stable and properly aligned. Once you have positioned everything correctly, go outside and fully drive in the screws to secure the hinge side of the door. Double-check that the door opens and closes smoothly before moving on to the next step.
Step 5: Adjust and Secure the Latch Side
Step outside and gently close the door. Look at the weatherstripping along the edges and check if it touches the door evenly at the top, middle, and bottom. If you see gaps, adjust the latch side of the door by shifting it slightly in or out until the weatherstripping seals properly.
Once the alignment looks good, drill pilot holes at the top and bottom of the latch side of the door frame. Partially insert screws into these holes to hold the door in place. Then, slide shims above the screws to help keep the frame stable and ensure it remains level.
Use a level to check and adjust the frame if it is not plumb. If you have correctly aligned everything, fully tighten the screws at the top and bottom. However, leave the middle screw loose for now so you can make any final adjustments if needed.
Step 6: Install the Strike Plate
Next, close the door and check that it latches properly. Place a shim above the strike plate location to provide additional support. Then, fully drive in the last screw to secure the frame.
After that, insert another shim behind the strike plate location to reinforce the latch side of the door. Once the frame is stable, align the strike plate with the latch and secure it with screws. Make sure the door closes smoothly and locks into place without resistance.
Step 7: Check the Door Fit and Make Adjustments
Now, you need to ensure that the door sits snugly against the adjustable sill cap. Take a piece of paper and place it between the door and the cap. Gently pull it out. It should have a slight resistance but should not tear.
- If the paper slides out too easily, the fit is too loose.
- If it tears, the fit is too tight.
To fix this, adjust the cap screws to raise or lower it until you achieve the right balance. Once you have adjusted the fit, seal the corners along the edges using caulk and install the self-stick corner pads for a secure and complete installation.
Step 8: Install the Locks and Trim the Shims
At this stage, you will need to install the lockset and deadbolt. Follow the manufacturer’s instructions carefully to install both components securely. Once in place, test the lockset and deadbolt several times to confirm they function properly. If there are any issues, the alignment should be adjusted until everything is correct.
Next, cut the shims to fit using a utility knife. Carefully score the shim a few times and snap off any excess. Alternatively, you can use an oscillating tool to make the cuts more precisely and quickly. Ensure that you cut the shims flush with the frame to avoid any interference with the door’s function or appearance.
Step 9: Insulate the Frame and Install the Interior Frame
To help keep cold air out during the winter, place blanket insulation around the frame. Start by cutting the insulation to fit snugly around the entire perimeter of the frame. Ensure the insulation fills any gaps or spaces where drafts could enter. This will help improve energy efficiency by preventing heat loss and keeping the indoor temperature stable throughout the colder months.
Next, install the interior frame by carefully positioning it within the door frame. Align the frame properly, and make sure you square and level it to avoid any issues with door operation. Secure the frame in place using screws or fasteners as recommended by the manufacturer.
Step 10: Finishing Touches
Seal the interior and exterior joints to create a weather-tight barrier and prevent air or moisture from seeping through. Choose and apply a high-quality caulk or sealant suitable for exterior use. Apply an even bead along the joints, then smooth it out with a caulking tool or your finger to ensure complete coverage.
I also asked Christopher Gaetzke for his expert advice on the best weatherproofing techniques to seal an exterior door against drafts and moisture properly.
He explained, “The best weatherproofing system is a combination of quality butyl flashing tape on the sides and top and wide flashing tape for the sill. Once the new door is secured and flush with sheathing and drywall, you need to seal the gap between the jamb and framing with butyl tape and quality siding sealant.
“Then, you install your exterior brick molding or other low-maintenance trim. Fill the gaps from the interior with window and door spray foam. Only fill about 40% of the space to allow for expansion.
You’ll need to seal the exterior molding and the bottom of the jamb legs above the sill with silicone to prevent water from wicking up the jamb legs. Lastly, adjust the bottom gap between the threshold and the bottom of the door with the hinge adjusters. You’ll know you’re set when you can pull a dollar bill under the door with moderate resistance.”
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Related articles:
- How to Hang an Exterior Door in an Existing Frame
- How to Hang a Prehung Interior Door
- How to Hang an Interior Door in an Existing Frame
Main Photo Credit: Jason / Adobe Stock Free / License
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