I'm working on a doorway, in a basement stairwell. The exterior door is fine. But the interior door, down the stairs, which separates the basement from the stairwell, is leaking heat out on 3 sides. I installed one of those gaskets on the bottom of the door which solved most of the problem of cold air leaking in under that door. I say 'most' because there's still an issue at both corners, which installing weatherstripping or moulding should solve. I also cut out the bottom of the doorframes, on the outside of the door, that the door bumps into, because they were rotten, and replaced them with fresh lumber. Then I used wood filler to repair the door and fill in some gaps in the frame. But there are still gaps on 3 sides when the door is closed. Here's a drawing:


Looking at it from this viewpoint, the door swings in, away from you. Theoretically, I can install moulding on the outside doorframes shown by the green arrows. Obviously not on the inside because then the door wouldn't open. Installing moulding would be perfect on the side where the hinges are. It would totally block cold air and bugs from getting in on that side. And it wouldn't ever fall off like weatherstripping does. But it would look weird if there's no moulding at the top and on the side where the doorknob is. So to totally solve the problem, and make everything symmetrical, I would install the same type of moulding on the doorframe at the top and also where where the door swings closed. I want to know if I should do it this way, or would that be a mistake? Should I just install weatherstripping?

 

Molding itself isn't really intended to seal anything, it's more of a finish detail.

Sealing gaps is the job for various types of foams and seals.

Now that is not to say that an oversized molding could be installed to help hold a seal.

Tough to say based on information provided!

 

If you feel like you need to put weatherstripping on an interior door, then that door should probably have been an exterior door in the first place... not an interior door. Just like the door from a garage into a house is always an exterior door.

 

I recommend a factory prehung exterior door if you can find it narrow enough.
It might weigh 80 lbs. so have a helper.

 

@xsleeper I think it was the exterior door when the house was originally built, 100 years ago, when they didn't care about things like finishing basements, water infiltration, and heat loss. But later they put in concrete stairs going up to ground level and enclosed those stairs. I just replaced the roof over the structure - that's explained in my previous thread. There's a steel exterior door at the top of the stairs. They never bothered to tear down the door or its doorway at the bottom of those stairs, because there was no reason to. I'm just trying to improve what's there.