If it’s time for a new roof on your home, you may be wondering if you can just put a new layer of shingles over your shingle roof in Arizona.
The short answer is yes, you can, but it may not be a good idea. There are situations when you should remove your existing roof and start from scratch and others when you may be able to install a new roof over your existing roof.
The Layers of a Roof
Your roof may appear simple compared to other aspects of your home. However, many layers and materials go into creating a strong, reliable, and safe roof.
Insulation
Roof insulation is a barrier material that lays between the rafters. Proper insulation slows the transfer of heat between the outside world and living space, keeping your home cool in summer and warm in winter.
Insulating the roof well retains energy in your home and reduces the heating and cooling load on the HVAC system. Roof insulation also prevents damage from ice damming, which occurs when the warm air tries to escape through the roof.
Ventilation
The attic is part of a roof system and needs to be adequately ventilated. The general purpose of roof ventilation is to encourage airflow through the attic space to maintain uniform temperature and humidity.
Ventilation systems have intake and exhaust vents installed at strategic intervals. Common types of ventilation include ridge vents, gable vents, and static vents. The roof ventilation system lowers the likelihood of ice dams and keeps your home comfortable.
Roof Deck
Also known as sheathing, the roof deck is a layer that’s installed over framing and provides a base for the other layers. The material used for sheathing varies, but most homes use plywood or OSB sheets. Reinforced concrete, corrugated metal, polystyrene, and double tee may also be used.
Underlayment
Underlayment is a protective layer installed onto the roof deck that adds a layer of water resistance against leakage. The most common type of underlayment is felt.
Ice and Water Shield
A waterproof membrane offers a sticky surface to adhere to the roof deck and forms a watertight seal around nail penetrations. The entire roof can be covered with ice and a water shield to prevent intrusion into your home.
Ridge Vents
Ridge vents are installed at the peak of a sloped roof and help with ventilation. They’re generally covered by roofing materials. Venting allows the hot air in the attic to rise naturally and release into the outdoors, providing uniform cooling.
Roofing Material
The roofing material you choose is the final layer. Homeowners generally choose shingle, shake, metal, tile, wood, or slate. These roofing materials are essential for the aesthetic and function of your roof.
Flashing
Roof flashing is a flat, thin, waterproof material at the intersections of different roof planes. Flashing may consist of materials like steel, zinc alloy, aluminum, and copper. Flashing is rolled into place and sealed to prevent water penetration of vulnerable areas like walls, vents, and chimneys.
Benefits of Installing a New Roof Over an Existing Shingle Roof
Some Arizona homeowners choose to install a new shingle roof over existing shingles because:
It’s less expensive.
You won’t have a dump fee for removing your old roof, and you won’t need to get additional felt paper.
It’s less of a hassle.
The installation period is much shorter if you don’t have to tear off an old roof and start from scratch.
It lasts just as long.
If your roofer installs the new roof correctly, putting new shingles over old ones can last as long and look as good as a completely fresh new roof.
It has the same manufacturer’s warranty.
Manufacturers will still warranty a roof for the same amount of time as a re-roof if a qualified installer performs the work.
It provides added protection.
If your old roof is in good condition, the additional layer of a new roof can serve as added protection if storms or high winds blow off shingles.
Benefits of Starting from Scratch
Even with the benefits of installing a new roof over an old one, there are times when it’s better – or necessary – to tear off the old roof and start from scratch.
- If there are already two shingles layers, most building codes won’t allow a third.[1] So, if this is the case, you need to tear off the roof and install a new one.
- If your current shingles are curling or in bad shape, the new shingle roof can’t lay flat as it should. If your roof has damage like this, it’s better to remove it and install a new roof.
- Roof leaks are another reason to ditch the old roof and install a new one. Removing the old roof will reveal the source of the problem, not to mention that installing a new roof over a leaking roof won’t correct the leak. Over time, this can cause damage to the interior of your home.
- If your roof is soft and spongy, there’s an issue with the sheathing of the roof. You will need to remove the existing roof and install a new one to correct this.
- Your roof may not be able to support the weight of a new roof on top of an existing roof. The shingles need to cover about 2,000 square feet of roof, weighing about 5,000 pounds, which is more than some SUVs. If the roof’s underlying structure can’t support this, you will need to take your old roof off and install a new one.
Install Your New Roof in Arizona with Four Peaks Roofing
Professional installation matters if you’re considering re-roofing or installing a new roof. The licensed, bonded, and insured contractors at Four Peaks Roofing have decades of experience installing and re-roofing Arizona homes. Contact us today to schedule your consultation!
Sources:
[1] https://codes.iccsafe.org/codes/arizona
