When installing an exterior door, be sure to not to install the door too low. When this happens, there is no room for a rug on top of the finished floor. Sometimes the door even drags on the carpet.
The sill that comes attached to the door is normally 1-1/4 inches high. When you start to add underlayments and flooring that space can disappear quickly. Be aware, when you purchase an adjustable threshold on your door, that does not mean you can raise the height of the sill. That just means you can adjust were the sill comes in contact with the bottom weather stripping.
This problem is totally avoidable if you add extra height to the rough opening by installing an extra piece of lumber on top of the subfloor prior to installing the door. Usually a 1/2 or 3/4" thick piece is enough to allow room for a rug or thicker carpeting. Also, be aware if using ceramic tile, an underlayment will be installed on top of the subfloor. This too can cause problems. When you know this in advance, you or the homeowner will be much happy with the installation. Homeowners, or even worse, your wife will get frustrated every time the door is opened and the rug slides away with the door. I'll bet you will get a phone call on this one. Most contractors usually only make this mistake once.
The point here is to be aware of what you will be installing on the floor and their thickness. Another tip, you may need to increase the height of the rough opening
to allow the door to be raised. The door height is not tied to the subfloor but rather the height of the finish floor. Planning ahead can save a lot of headache down the road!