DEAR TIM: I'm going to build a room addition myself because money is very tight. Can you help me understand how I frame in the door openings? I've never done this before and am very confused. Is the method the same for all doors? How wide and tall do you make the opening? What do I do on an exterior wall? Elizabeth S., Denver, CO
DEAR ELIZABETH: I first want to congratulate you on your ambition and wisdom in asking questions before you get in trouble. No doubt it's easy to jump into a project, but in these very harsh economic times, you can't afford to waste any money on mistakes. Ask enough questions and you should be able to get through this daunting project.
The first thing to understand is there could be a concentrated load above a door. This happens on bearing walls. In these instances, there's a structural header that acts as a beam over the door to support the load or weight that's bearing down on that portion of the house.
Bearing walls can be both on the exterior of the house as well as on interior walls. In the last house I built for my family, I had an interior bearing wall with a door in it. Immediately above the door was a concentrated load that I'd estimate was about four tons. You can bet I had a double 2x12 header above that door! Headers come in all sizes and usually a structural engineer or an architect will size them for you.
A doorway in a non-load-bearing wall doesn't need a structural header. You'll place just one or two 2x pieces of lumber flat across the top of the opening. This framing lumber is used to support the finished wall material and provide solid nailing for any trim around the door. It also acts as a tiny bottom plate for the cripple studs above the door opening that reach to the top plate.
When you frame a door, it's very important that you use the straightest pieces of framing lumber that you can find in the pile. What's more, you frame the door with a continuous bottom plate just as the wall has a continuous top plate. The bottom plate at the doorway gets cut out after the wall is in place, secure and the bottom plate is securely fastened to the floor.
Door openings commonly have two king studs and two jack studs. A king stud is one that runs continuously from the top plate to the bottom plate. The jack stud is nailed to the king stud, but it's shorter as it supports the structural header or the flat 2x material that you use for a door in a non-load-bearing wall.
You may have to install small cripple studs between the top of the header and the top plate. These need to be a continuation of the other king studs on the wall being sure to maintain the even 16-inch or 24-inch on-center spacing you have for the finished wall material.
The width and height of a rough opening for a door is very important. Your plans may call for a 3-foot-wide door that's 6-feet 8-inches tall. From years of experience, I'm here to tell you that the rough opening should be at least 38 and 1/4 inches wide and the height of the opening should be 84 inches.
You must keep in mind that exterior doors have a threshold that's often at least 1-inch high and that the bottom of this threshold MUST be installed at the same elevation as the top of the finished floor in the house. Rookies often forget this making the rough opening too short.
Height considerations are the same for interior doors. These doors are set on the finished floor and there is almost always a 1-inch air gap under the door after it's installed.
Just do the math for exterior doors. Here are the things you need to consider: the actual door height, the thickness of the weatherstripping under the door, the thickness of the threshold, the thickness of the finished floor, the thickness of the finished top door jamb, and then add about one-half inch wiggle room for shims and other site conditions.
You do the same exercise to figure the rough opening for door width. You add the actual width of the door to the thicknesses of both finished jambs, plus add about 3/4 inch for shims and wiggle room.
It's mandatory that the rough opening for a door be in the same plane. This is one function the top and bottom plates of a wall perform. If the plate material is straight, the bottom plate is installed perfectly straight and the wall is plumb, then the wall and opening will be in the same plane.
NEVER plumb a wall putting a 4-foot level on the wall studs. If the stud the level is resting on has a crown or hump in it, the level will not give a true reading.
You plumb a wall using a perfectly straight piece of lumber that only contacts the top and bottom plate. Place this lumber between king stud locations so it's only touching the wall plates.
You can watch a great video about framing a door here on my AsktheBuilder.com website. Just type: Framing a Door in the search engine once there.
