Install the Drip Edge: Your first step is to apply a drip edge to the eave and cut drip edge flashings at the corners, pressing them lightly on the eave end. Now lightly hammer in a nail at the end, and always align the material using the chalk line.
2. Overlap and Cut Drip Edges: Make sure you overlap meeting drip edges by 2 inches and when they meet in a valet, cut the overlapping tabs and press these tabs firmly to form a seamless, clean corner.
3. Align the Felt: Roll out around 12 feet of material using the chalk line as a guide. Make sure there are no creases or bubbles and reroll and unroll to make sure of this. While unrolling, peel off the paper backing.
Try adhering to the bottom half first on steeply angled roofs. You can also apply the underlayment at the same time as the felt during dry spells. After this install the shingles. Add more felt when you are 6 inches away from the top edge.