Padded or foam-backed carpet is not designed for heavy-traffic areas but is ideal for spare bedrooms.
Clean the Floor
Remove the old carpet and clean the floor thoroughly. Remove as much dust as possible to enable the adhesive carpet tape to work best. If you find irregularities in the floor, especially small bumps, remove or fix these. They will soon wear through a foam backed carpet.
Apply Carpet Tape
All around the outside edge of the room (if the carpet will cover the whole floor), apply two rows of adhesive carpet tape but do not remove the upper side backing. You will remove the backing when you fit the carpet.
Position the Carpet
Open up the foam-backed carpet and match the long side to the longest wall in the room. Start at a corner and push or pull the carpet into place. Once the carpet is flush against the long wall, you can start to remove the backing of the adhesive carpet tape and allow the carpet to settle into position. Remove the backing a short length at a time so that you have full control of how the carpet behaves.
Install the Carpet
Continue in this way until the carpet is fixed against all the walls. Don’t worry about bumps in the foam-backed carpet. These will flatten out quickly. Make sure you remove all the backing from the adhesive carpet tape and that you do not leave it under the carpet.
Trim the Carpet
If there are irregularities in a wall, use a sharp knife or shears to make the carpet fit around them. Press the carpet against the base of the irregularity and then use a sharp knife to cut from the edge of the carpet to where the irregularity ends. Make this cut should be at a downward angle so you can make a proper fitting once the carpet lies flat.
Install the Threshold Strip
Because the carpet is neither heavy nor tightly fixed to the floor, you must protect the edge that is exposed in the doorway. Use a metal threshold strip that will be nailed or screwed to the floor and which has a trailing edge that will cover the carpet.
Foam-backed carpet is not very strong, so you cannot use tacks to fix it to the floor; they would just pull through. Nor can you use tackless strips; they will just chew up the foam backing. As a result, every time someone walks on it, the carpet will move. The best thing to hold foam-backed carpet in place is furniture. But the worst thing you can do to foam-backed carpet is drag furniture across it.