How to Repair a Rotted Exterior Door Frame

This project shows how to repair a rotted exterior door frame by sawing out the rotted section and splicing a new section of door jamb. The repair cost about $100 in materials for a new door jamb, brick mould, weatherstripping, door corner seal and caulk.

Door frames commonly rot at the bottom corner where it meets the door sill. The wood jamb rotted because the caulk seam failed allowing rain water intrusion:

Rotted Exterior Door Frame

Rotted Exterior Door Frame

And the repaired door jamb with new PVC brick mould, weather stripping and door corner seal:

Rotted Exterior Door Frame - Finished Repair

Rotted Exterior Door Frame – Finished Repair

Note: A door frame has four parts: 1) left jamb, 2) right jamb, 3) header and 4) sill. The door hinges are fastened to the door jambs. I’ll use the terms “door frame” and “door jamb” interchangeably.

Check Soundness of the Door Sill

The door jambs are fastened to the door sill and partially stabilizes it… although not well if the jamb is rotted. Place both hands on the outside edge of the door sill and try wiggling it. The sill should not be loose. If the sill is loose stabilize it by filling underneath it with GREAT STUFF Window & Door expanding foam and/or caulk. For complete details see How to Replace an Exterior Door.

How Bad is the Wood Rot?

The wood rot may appear to be cosmetic but appearances can be deceiving. Once water intrusion begins it can wick into the 2×4 framing and rot the sole plate, subfloor, band joist and sill plate. Repairing structural damage is a major job and expense.

I probed the rotted door frame with a wood chisel (a flat-head screwdriver will also do) to check the extent of the rot. The wood was soft and crumbled. It had rotted completely through the jamb:

Exterior Door Frame Jamb - Probing Rotted Wood

Exterior Door Frame Jamb – Probing Rotted Wood

Rotted Exterior Door Frame Repair Options

I considered patching the rotted section with wood filler or Bondo® but the challenges are:

  • Wood filler isn’t designed to fill large and deep voids.
  • Bondo can fill large voids however all the rot must be removed so it has a firm foundation. Bondo also requires extensive shaping and sanding so it matches the original shape of the door jamb.

I decided the simplest solution was to cut out the rotted jamb and splice in a new 6 inch long section.

How to Repair a Rotted Exterior Door Frame

I used the following tools in this repair:

  • Claw hammer
  • Pry bar
  • Tape measure
  • Combination square
  • 3-in-1 caulk tool
  • 1 inch wide putty knife
  • Pencil
  • Wood chisel – to scrape off the old caulk
  • Flat-head screw driver
  • Needle-nose pliers – needed to pull wood staples or nails out of the sill
  • Brad Nailer with 2 inch brads
    A hammer and finishing nails may be used instead, however it’s way less convenient.
  • Portable air compressor for the brad nailer.
  • Compound miter saw to cut the new door jamb and brick mould.

and materials:

Saw out the Rotted Door Jamb

Pull the door weatherstrip out of the jamb. It’s in the way and I’ll install new weatherstripping later:

Remove Door Frame Weather Strip

Remove Door Frame Weather Strip

The brick mould will have to be pried off to install the new jamb splice. Cut the caulk line with a utility knife on both sides of the moulding along the entire length:

Exterior Door Frame Repair - Cut Caulk with Utility Knife

Exterior Door Frame Repair – Cut Caulk with Utility Knife

Mark and Saw the Rotted Door Frame

Mark a horizontal line on the door jamb using the combination square at a location several inches above the rotted area, taking care to avoid any nail heads that would damage the saw blade. My line is about 6-1/4 inches above the sill but well below the load-bearing area at the door hinge:

Rotted Exterior Door Frame Splice Repair - Mark Saw Line

Rotted Exterior Door Frame Splice Repair – Mark Saw Line

An oscillating multi-tool with a saw blade attachment is perfect cutting the door jamb. The blade vibrates back & forth through a narrow arc. You’ll hear a change in pitch when the blade cuts through jamb. Make several straight-in plunge cuts along the pencil line. Keep the saw blade horizontal or angled slightly upward so the new repair splice doesn’t get pinched. Great precision isn’t required and the long blade will guide itself:

Exterior Door Frame Repair - Saw Out Rotted Section

Exterior Door Frame Repair – Saw Out Rotted Section

I had to make a second cut just above the sill because the bottom of the jamb was fastened with 4 wood staples (your jamb may be nailed). I used a flat head screw driver and hammer to split jamb into sections and pulled out the pieces:

Exterior Door Frame Repair - Split and Remove Wood Fastened to Door Sill

Exterior Door Frame Repair – Split and Remove Wood Fastened to Door Sill

Rusty staples were in the side of the sill. I had to twist the broken staples around the needle nose pliers to pull them out:

Rotted Door Frame Repair - Remove Sill Staples

Rotted Door Frame Repair – Remove Sill Staples

Scrape and vacuum out any wood rot in the pocket. I had some superficial rot on 2×4 framing but it was only 1/4 thick.

The door frame after sawing out the rotted jamb:

Door Frame Repair - Rotted Jamb Cut Out

Door Frame Repair – Rotted Jamb Cut Out

The wood brick mould was starting to rot (see the above photo) and it must be removed to install the new jamb splice. You can remove the brick mould before sawing the jamb which may make it easier to wiggle out the rotted piece. After cutting the caulk line on both sides of the brick moulding, I pried it off using a claw hammer and pry bar (see this project for details). The old moulding is trash and I’ll install a new one:

Remove Exterior Door Brick Mould

Remove Exterior Door Brick Mould

Shave off the remaining caulk on the door frame and siding using the wood chisel for a smooth surface. The chisel’s sharp flat blade makes for quick work.

Exterior Door Frame Leg (Door Jamb)

Most houses with 2×4 wall framing have a standard size 1-1/4 in. thick x 4-9/16 in. wide x 84-1/16 in. tall door jambs. It’s sold at the home improvement store individually as a “door frame leg” or as a three-piece kit (left & right jambs plus the header). Exterior jambs are beveled at the bottom to match the slope of the sill plate. Note the sill bevel is the following image is for left side of the door, however I’m repairing the right side of the door as viewed from the outside. Therefore I can’t use this particular jamb leftover from another job:

Exterior Door Frame Leg - Bottom Sill Plate Bevel

Exterior Door Frame Leg – Bottom Sill Plate Bevel

View of the door jamb and slot for the weatherstripping:

Exterior Door Frame Leg - Weather Strip Groove and Sill Plate Bevel

Exterior Door Frame Leg – Weather Strip Groove and Sill Plate Bevel

The top of the jamb has a straight cut for the door frame header:

Exterior Door Frame Leg - Top End

Exterior Door Frame Leg – Top End

A profile view of section cut from the door jamb:

Exterior Door Jamb Profile with Weather Strip Slot

Exterior Door Jamb Profile with Weather Strip Slot

PVC versus Wood Door Jambs

Door jambs and brick moulding are available in wood or PVC plastic. Polyvinyl Chloride (PVC) products are also described as “composite” or vinyl material. I prefer PVC because it cuts & works like wood, is paintable and water-, insect- and rot-proof.

For this repair I purchased a Wood Jamb Primed Finger Jointed Pine Door Frame Moulding and PVC Brick Moulding from Home Depot. I would have preferred a PVC jamb but Home Depot only stocked 3-piece PVC frame kits. I plan to replace the entire french door next Spring so a wood jamb is acceptable for now.

The new wood door jamb for the right side of the door. This jamb includes the weatherstrip:

Exerior Door Frame Leg with Sill Plate Bevel

Exerior Door Frame Leg with Sill Plate Bevel

This project is continued in Rotted Exterior Door Frame Splice Repair.

Thanks for reading,

Bob Jackson

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