Exterior trim around a sliding patio door.

Improving The View:

Installing Exterior Trim
Around A Replacement Door

In This Article:

1x4 trim is nailed around the perimeter of a slider door, after special flashing is installed.

Related Articles:
Skill Level: 3 (Moderate) Time Taken: 2 Hours

By , Editor

Touching up the trim around the outside of a new sliding door need not be difficult. The type of siding on the house will determine the ease of repair. Wood siding is the easiest to repair. Vinyl siding can be tricky, but there are solutions. Aluminum siding is difficult to patch because it bends easily and is hard to cut cleanly.

Read Framing The Rough Opening to see the first article in this series, and Installing A Sliding Patio Door for the second article.

The first thing we did was apply a flashing around the door frame. This material is a rubberized asphalt type of membrane. We used it because the homeowner had no other suitable materials.

 In the old days we used roofing felt (tar paper) for flashing around window and doors, but rubberized asphalt products such as Vycor® or Grace Ice and Water Shield

This is the product we used, leftovers from a previous job.

Some carpenters do not bother with flashing around windows. But it takes only a few minutes and can make a world of difference if water somehow gets behind the siding or trim (such as during a powerful thunderstorm). The idea is to guide stray water droplets away from the plastic flange of the window or door frame. Like siding boards, the material is applied from bottom to top, with an overlap that keeps water on the outside of the flashing.

The flashing material is placed across the bottom flange. Note how the flashing spans from the underside of the door frame down to the siding board below. Any water that reaches the flashing will be directed over the top surface if the siding.


Next, a piece of flashing was attached along the sides of the frame. This material is (sort of) self-adhesive.

Note how the flashing overlaps the lower piece, preventing water from getting behind.


The flashing was installed on the sides of the frame, up to the top and beyond a few inches.

Note section of siding we removed above the door. This will be replaced after flashing is completed.


The top section of flashing was installed. It overlapped the side pieces.

The adhesive did not hold well so we stapled the flashing to the fiberboard wall sheathing.


The next day we returned with a roll of red rosin paper and applied a wide strip at the top, making sure to slide it up and under the section of siding above the door.


Now for the trim.

A piece of 1x4 white-wood (spruce-pine-fir) was cut to the width of the door. We secured it with 2" nails from a pneumatic nailer, but ordinary galvanized finishing nails would work fine.


Next we installed the side pieces that go from the bottom of the lower trim...


... to the top of the door frame.


The top piece runs the full width of the door plus the two side pieces of trim.


We had salvaged the cedar siding when we cut out the door opening, so we selected two good pieces.

We ripped the siding on the table saw so it would fit above the trim.

Note that the best method of construction for this above the door detail is to use a metal (typically aluminum) Z-flashing, where one leg of the "Z" shape goes up under the siding board, and the other leg of the Z goes over the top of the 1x4 trim. I believe that this metal flashing may also be called a "drip cap". 

Earlier, we had driven some wedges between the rows of siding to raise the upper piece.

The original nails used were aluminum (on the right). We replaced them with hot-dipped galvanized siding nails, which are thinner and less likely to split the wood.


The siding above the door was replaced. All that remains is to caulk:
1. between the vinyl door frame and the trim
2. between the trim and the siding.


The completed door trim and siding repair.

After the caulking is finished, the trim will be primed and painted.

A few notes about inside trim:

  • Cutting into a wall to install a door or a window looks more difficult than it really is. This building is an annex to a shop that is being converted to a guest house, so there were no interior wall surfaces (such as drywall) to deal with. But doing major surgery on a finished house is within the skills of a moderately experienced handyman.
  • Installing a wide door requires a large header, such as the 2x12 header used here.
  • Installing a header in a new window or door opening would be almost impossible with the drywall in place. The wall surface in front of the header must be removed.
  • Cutting out and replacing a large section of drywall or plaster can be done, but the joint may be hard to conceal (curtains come to mind).
  • It may be worth considering removing and replacing the wallboard from the entire wall. This provides the fringe benefits of letting you update and improve the insulation and electrical wiring. Then the junction of the new and old wallboard occurs at the corners, which can be concealed with wood trim (for a quick fix) or drywall joint compound, which looks original but would then require painting of the adjacent walls and/or ceiling.
  • A door like this would require jamb extensions to make a finished surface next to the door frame. Casing around the opening would complete the job.

WARNING: If you are going to undertake a project this big, make sure you completely understand all the steps involved. Consult your local building department and check if permits are required. We encourage our readers to look at other competent sources for second opinions, because the work shown here may not be applicable to your home.



Tools Used:

  • Pneumatic Nailer
  • Caulk Gun
  • Cordless Drill/Driver
  • 4' Level
  • Hammer, Tape Measure
  • Staple Gun
  • Table Saw or Circular Saw

Materials Used:

  • Lumber, 1x4x8'
  • Galvanized Nails
  • Window/Door Flashing


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Copyright © 1999, 2005  HammerZone.com

Written August 20, 1999
Revised January 9, 2005