Asphalt Shingle Roof Installation Process
First things first: you’ll want to start with a complete removal of existing roof systems. Many roofing companies offer to install a new roof over the existing structure. The problem with that is sometimes we can’t inspect the rotten plywood or OSB underneath, or we can’t see the spacing between the roof deck or verify the roof ventilation locations.
For these reasons, I would not recommend installing a new shingle roof over the existing one unless a thorough inspection, including a cut test, is done to make sure it is okay to create another roof layer. Also, be aware that manufacturers will not warranty their products if installed over an existing roof. We advise that you completely remove the existing roof down to the wood deck to ensure a high-quality shingle roof system installation.
Then a roof deck inspection should take place. Many older houses have sizeable gaps and spacing between the decking because of building settle over the years. When nailing the shingle, we need to make sure it is nailed through the plywood at the correct nailing zone and not between those gaps. Otherwise, it will not be properly installed; it will be easily damaged or lifted by the wind, and the roof will leak and fail, requiring another replacement.
We recommend installing metal drip edges along the perimeter of the house, the eaves and rakes. This helps prevent water from backing up from the shingles onto the fascia boards, soffit, and siding, which may rot and damage over time from the constant dripping water.
Next, the ice and water barrier is installed at the eaves, valleys, and all protrusions, especially on the north side of the house. The ice and water barrier should extend 2ʹ beyond the interior wall to achieve proper installation practises. Sometimes we install the barrier throughout the roof to prevent ice damming and water backing up, especially in lower-sloped roofs.
Then underlayment should be installed. Many years ago, this was a felt material. These days, we use synthetic waterproof underlayment, preferably from the same single brand manufacture (for warranty purposes).
The next product is the starter shingle. Sometimes roofing contractors use leftover shingles, installing them instead of the proper starter. The problem with that is wind-driven rain can cause roof leaks, whereas proper starter strip shingles have bonding adhesive to hold the shingle above in place and prevent it from lifting from the bottom.
The final accessories are the hip and ridge shingles. Every manufacture has specifically designed hip and ridge accessories for their products. Back in the day, some roofing companies would cut the three-tab shingles to create hip and ridge for their roof. Today, we follow the manufacturer’s instructions when installing all accessories and roof-related products to ensure we meet the relevant warranties. There are two types of hip and ridge shingles: low-profile standard hip and ridge and high-profile hip and ridge.