The entire old roofing system was torn off, including shingles and underlayment down to the clean deck. This is to ensure that any rotten woood can be seen and replaced if neccessary. High End Synthetic Felt was installed as the underlayment along with a leak barrier around all the roof penetrations (pipes, skylights, chimneys, vents).
Featured Timelapse: Re-roof Construction Process
This video shows the whole two day construction process, from removing the old shingles all the way down to the deck to adding ice and water shield, synthetic felt paper, etc. and eventually the new shingle.