Rotten Door Jamb / Sill

Should I replace my old rotten jambs and sill with a new pre-hung door? We get many emails asking about changing out rotting door jambs or door sills asking how to do it, and if is it the best solution. If you decide to undertake replacing just the sill and jambs, it’s not a project for the first time DIY’er. Don’t get me wrong, it can be done, but depending on the shape of the door itself, it’s normally less time consuming and less costly to replace the jambs with a new pre-hung door.


If the door sill is rotten, normally there is a reason. It could be the jamb was never caulked to the sill. When this isn’t done, moisture easily penetrates between the two pieces causing them to rot.


This can also cause water damage to the subfloor. Correcting the underlying moisture infiltration is critical before you fix or replace the door with a new pre-hung unit. Otherwise, you’re just wasting your time and money.


Bondo filler or the more expensive structural Wood Epoxy can be used to fill rotting areas. Sand it properly so there are no waves and then repaint. You could also cut out the sill and put a water return threshold to correct the water pooling situation. You could cut off 8 inches of the jambs, replace with custom milled sections (router, table saw) and then patch in the connection and paint. But all of that will take time and some power tools. The good thing, there isn’t much cost to materials, so if you have the tools and time it’s not a bad way to go.


Installing a new pre-hung door is often the best choice. You will get a new door, jambs and sill. Don’t be fooled into thinking just because you install a new door that your problem is solved. If you don’t properly flash, caulk, paint and install sill protection, you could be repeating your project in just a few short years. I have seen many door installations fail in less than 5 years if they are not completed properly.


 Door Sill

In new adjustable sills, water that gets through the sill is channeled out the bottom. This is why it is imperative to install something under the sill (sill pan or butyl tape) to keep moisture off the subfloor.


Yet another option is to buy composite or non-wood material jambs. There are a few companies offering this option in new pre-hung doors. Some have incorporated composite on the bottom 12” of the jamb combined with regular wood jambs for rest of the door. These products are good, but the cost can be more than double of normal wood jambs.


So here are the things to be sure and check for:

  • Proper flashing or drip cap above the door
  • Caulking where the jamb meets the sill
  • Back caulking the brick-moulding prior to setting the door
  • Back painting and full painting of all exposed and non-exposed wood
  • Keep all weep-holes open on the sill


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