Good underlay is an important detail that must not be forgotten. It absorbs sound, prevents rising damp from below and evens out small irregularities.
Underlay is very simple to lay; you only need a knife and a ruler. Roll out a piece of underlay and push it up to the wall. Put a box of planks on it to hold that end in place before rolling out the rest in the other direction. Then tear it off at the nearest perforated edge.
To fill the remaining gap between the underlay and the wall, measure it and make a mark on the piece of underlay you want to use. Draw a dot on both sides and then use a plank to cut between the dots in a neat, straight line.
Then put the piece you have cut out in place. It is important that the underlay lies flat and the pieces do not overlap. Otherwise, the floor may become uneven and unstable. If this happens, cut the pieces so they fit better and lay them again.
If any of your walls are not at a right angle, you will have to measure the length and the angle. Cut out one corner and then use a plank to continue cutting so that you get a straight edge. If there is a piece of underlay against a wall at a right angle on one side and a wall that is not at a right angle on the other side, start by laying the underlay against the wall that is not straight to make it easier to position it correctly.