Hi. I want to replace my front door with a standard 3-0 door but my rough opening on my existing door is 85.25 inches in height. This is a brick home built in the 1960s. In order to do this I understand that I would have to fill in the extra ~3 inches. I assume that I can incorporate 2x4s above the frame on the inside. However I do not know what to do on the outside. I have a porch covering so it wouldn't receive direct rain or snow. I see some neighbors homes that have had the door replaced and they have what looks like wood or composite material on the outside to fill it in but what would you recommend to use or how best would one weather proof the area?

 

Rough opening refers to the height of the framed opening... from subfloor to header... and from the 2x4 on the left to the 2x4 on the right. On a brick house, you are also limited by the brick opening, (masonry opening) which is typically several inches larger than the rough opening is.

Typically old doors have a wood sloped sill on the bottom. The floor joists were notched out so that top edge of that door sill would end up being flush with the finished floor. Then a wooden threshold covered that gap... and the door would swing above that.

If that is what you currently have, replacing it with a modern standard door takes a little planning and thought.

Your new door will likely have an aluminum sill and threshold. It is meant to sit on top of your subfloor. But the height as which it sits (the bottom of your rough opening) often needs to be adjusted based on the thickness of your finished floor. A thick finished floor like cement and tile would mean you would need to shim the door up (install the door higher) or else it will drag on the floor... or be so low that you can't put a rug in front of the door.

The measurement of most 6-8 doors that come with brickmould will be around 83 1/4" as measured on the outside from the bottom of the sill to the top of the exterior trim. They fit in a rough opening that is 82 1/2" or so, because the height of the complete door jamb is usually around 82". (Exact measurements will vary)

So if your opening is 85.25", it is not a simple thing of just adding 3" to the top... or 3" to the bottom... or even 1 1/2" on bottom and 1 1/2" on top. You kind of need to figure out where the door needs to sit, so that when the door swings, it clears the finished floor the right amount.

You'd be surprised how many people set the door, then they have to try to find a thinner rug. Or find out it's too low to have a rug at all!

As for what to use, I'm partial to using PVC like Azek. (Since you never want it to rot.) And typically it needs to be flat and level where the door sits, but sloped on the outside beyond the new door sill, to shed water. So I will build up a flat, level RO for the door to sit at the correct height, that extends out the the edge of the wall sheathing, and then after the door has been installed, add a sloped sill nose onto the front. Or a step sill, (2 sloped pieces) if a single piece looks too thick.

Does any of that help?