When installing carpet, you'll notice a slight variance in baseboard height, which is typically between 1/4 inch and 3/8 inch. An easy way to space baseboard off the floor for carpet is by using precut 1/4-inch shims as spacers, which will provide a consistent height throughout the room. A spacer is a piece of material set between a stationary object and the material you're installing. In this case, the spacer is set on the subflooring, and the baseboard is then set on the top of the spacer. The baseboard is then installed and the spacers removed.
Cut two scrap pieces of material, about 4 to 5 inches in length, from 1/4-inch material such as wood shims.
Place a fitted piece of baseboard on the floor next to the wall where you're installing it. Lift up each baseboard end and place a 1/4-inch spacer underneath.
Press the baseboard firmly against the wall. Place a 1 ½-inch finish brad nail near the bottom of the baseboard, by hand or with a finish nail gun, so it will penetrate the bottom plate of the rough framing inside the wall. Space each nail 16 to 24 inches apart across the entire length of the baseboard when securing.
Remove the spacers from under the installed baseboard and reuse them to space and fasten additional pieces of baseboard until the entire room is complete.
Countersink any finish nails with a nail set tool if they're hammered in place by hand or if the nail gun did not work properly. Place a small amount of caulking or drywall spackle on your finger and fill in each hole for a finished appearance.
Paint the trim to your liking and let it thoroughly dry. Install the tacking, padding and carpet. Butt the carpet to the baseboard or press it underneath with the aid of a long-slotted tool.