Many homeowners often ask whether one can install a new roof over the existing roof. It saves cost and is faster. Moreover, two shingle layers seem stronger. So, should you do it?
Unfortunately, it’s not an easy question. While it’s practical, the disadvantages often outweigh the advantages.
Read on to learn when the second layer of shingles makes sense, when it doesn’t, and the best way to install an extra shingle layer over an existing roof.
How to put a second shingle layer on an existing roof
To put the second layer of shingles on your roof, proceed as follows;
- Evaluate the job
- Examine the existing roof
- Begin by making repairs
- Install the second layer of shingles
- Install cap shingles
Is it OK to have Two Layers of Shingles?
Yes, it’s OK to have two layers of shingles installed on your roof in most states. Indeed, some states allow three or even four shingle layers. However, the requirements vary from one state to the next. So, it’s best to check with your local building department.
For instance, you’re limited to two shingle layers in Texas. If you experience leaks and other issues after that, you must replace the roof. The same applies to New York, Montana, and North Carolina.
However, does it solves common roof problems? Unfortunately, not always. Although a double shingle layer makes your roof more resistant to impact, it has multiple downsides that make it ill-suited for most reroofing projects.
Pros and Cons of the Second Layer of Roof
Below are the pros and cons of installing multiple layers of shingles on your roof to help you make an informed choice.
Pros of Multiple Roof Layers
The two main advantages of roofing over an existing roof are increased convenience and lower reroofing costs.
- Faster roofing process: Convenience is the biggest advantage of roofing over an existing roof. For instance, uninstalling the existing roof is often a big headache and takes almost half the reroofing time. Fortunately, you don’t have to tear off the existing roof when roofing over an existing shingle layer.
- It’s cheaper than a new roof: Eliminating the uninstallation process reduces labor costs by at least 25%. Moreover, you need fewer materials. Therefore, you can eventually save up to 40% of the costs.
- Greater impact resistance: Finally, a two-layer shingle roof is more resistant to impact. For instance, falling tree branches are less likely to punch a hole through the roof. The shingles are also less likely to succumb to light winds.
Problems with Two Layers of Shingles
Unfortunately, roofing over an existing roof comes with multiple downsides. The following are common challenges to beware of;
- It’s difficult to detect leaks: It’s extremely difficult to accurately pinpoint the source of leaks with two layers of shingles on your roof. First, it takes ages to determine whether it’s the lower or upper shingle layer. Secondly, tracing the leak source often means probing a larger surface area.
- Extra weight issues: Though vital, the roof must not be too heavy. Otherwise, it puts excessive pressure on roof decking and framing. This is catastrophic as it may cause the structure to collapse. Added weight also impacts the walls and the home’s foundation.
- It impacts roof ventilation: Breathability is a key feature of modern roofing materials and structures. Unfortunately, the second layer of shingles erodes most ventilation gains. For instance, it creates an extra barrier, trapping heat between the shingles. The second layer may also block air vents on the existing layer.
- Moisture issues: An extra layer of shingles traps moisture, creating new challenges. For example, moisture causes faster shingle degradation and may trigger mold and algae growth. Worse still, the moisture often finds its way into the attic space, damaging the insulation, roof framing members, and the ceiling.
- It makes repairs difficult: Suppose you need to repair the old layer in a roof with two layers of shingles. Do you do it from the attic or cut through the new shingle layer? Similarly, how do you inspect the bottom layer? As you can see, it makes future repairs extremely difficult.
- Impact on warranty and local building codes: Installing a second shingle layer over the original roof may violate your shingle warranty and breach your local building codes. So, check with the roofing company and your local building departments before you proceed.
How to Install New Shingles Over Existing Shingles
Different professionals approach roofing projects differently. However, the following is the general process for roofing over an existing roof.
Safety Precautions
- Avoid bad weather: Winter, rainy weather, and extremely hot summer days are not ideal for reroofing projects. Also, avoid days with strong winds.
- Find a sturdy ladder: An old or damaged ladder is a disaster waiting to happen. In addition, position it firmly on the ground.
- Wear safety equipment: A helmet to protect your head in case of a fall, gloves to protect your hands when nailing, and safety goggles for eye protection are critical. Also, wear non-slip shoes.
- Wear a safety harness: A safety harness or fall arrest system can be life-saving if you fall from the roof. More importantly, ensure it’s in good condition and wear it appropriately.
- Always work with a friend: Have someone to watch your back while on the roof. For instance, your work buddy steadies the ladder when you get up or down the roof. They can also shout warnings and additional instructions from the ground.
Tools and Materials
- Enough new shingles
- Roofing cement
- New flashing
- Roofing nails (avoid screws)
- Utility knife/tin snips
- Chalk line
- Hammer/drill
Installing New Asphalt Shingles Over Old Shingles: Step-by-Step Guide
So, you’ve gathered everything you need for the project, including safety equipment. So. it’s time to get on the roof and begin the layover project. Here’s a step-by-step guide our professionals follow;
Inspect the old roof
Not all roofs are ideal for layover projects. For instance, installing a new roof is better if the existing one is badly damaged. Also, consider your building codes. Do they allow a second asphalt layer? In many states, you must remove the old layers to install a new one if you already have two layers of shingles on the roof.
Finally, thoroughly inspect the roof to identify areas where the roof deck is damaged and spongy sections with badly worn shingles. Mark these areas for repairs.
- Sweep the entire roof
A few people go straight to the repairs. However, we recommend sweeping the roof so you work on a clean, flat surface.
Use a regular broom to sweep the debris away. Alternatively, power-wash the roof and let it dry before commencing the reroofing job. Be extremely careful with vulnerable sections of the roof.
- Remove ridge caps
Removing the ridge caps now makes the rest of the process easier. Fortunately, removing standard ridge caps is easy. First, break the seal holding the caps down onto the shingles and against each other. Applying heat often helps. Then use a pry bar to lift the caps to expose the nails.
When the nails are sufficiently exposed, use a claw hammer to pull them out. Then gently lift out the ridge caps. Keep both the nails and caps safe for future use.
- Remove roof obstructions
Vents and flashing aren’t necessarily obstructions. However, they are when installing a roof overlay. So, it’s best to remove and store them safely to ensure a fairly flat surface. However, you can replace them if you wish.
It’s easy to remove the features. Break the seal around the feature, unscrew or pry it out, and store it safely.
- Make necessary repairs
If your inspection (in step #1) revealed major issues with the first course of shingles, this is the time to fix them. For instance, replace broken shingles and reattach loose ones. This step is critical because it ensures a flat surface for installing the new shingle layer.
Besides fixing loose and broken shingles, replace weak roof deck sections and reinstall missing nails.
- Install the flashing and valley flashing
Install U-shaped drip edge flashing at the eaves and rakes. You can also find specially designed rake edges for the rakes. These help direct water, snow, and ice away from the fascia board and into the gutter.
Drive nails at the high points of the bottom shingles of the underlying roof, ensuring the flashing features meet neatly at the corners. Do the same at the valleys (where present) using W-shaped metal or vinyl flashing. But this time, drive nails into the outside edges only.
- Install starter strip
Starter strips are the starting point of multiple roof layers. Rip-cut the strips such that they butt up against the new roof layer while sitting even with the front edge of the old layer.
- Install the new shingles
Again, rip-cut the shingles for the first course. You want them to butt up against the third course of the old shingles. In addition, they should sit even with the front edge of the starter strips. However, tab slots on the new shingles must not align with those on the old shingles. So instead, nail the shingles above the slots.
After the first course, continue to install the rest of the shingles until you complete the entire roof, butting the bottoms of the existing shingles.
- Work on vents and other roof features
First, work around the roof vent. Install the vent flashing, tear away excess sections of the rubber boot and apply roof cement around the flashing. Then cut the shingle appropriately to install air vents and the flashing. Do the same for chimneys and side walls. Then install the counterflashing and apply mortar with a caulking gun.
- Finish up
Trim the shingles at the ridge, snap lines on both sides, and install the ridge caps. When done, snap a line above the edge of the existing shingles and cut away the excess length with a utility knife.
How Long Does it Take to Install a Layover?
Installing a roof layover takes 1-2 days. It mainly depends on the roof’s size and shape and the required repairs. For instance, a small flat roof covering 1500 square feet or less is easily replaceable in a day if only a few repairs are required. However, larger, more complex roofs requiring significant repairs take up to a week to reroof.
What’s the Cost of Adding a Second Layer of Shingles?
Installing new shingles over old ones costs about 60% of roof replacement costs when you include material and labor savings. So, you can expect to pay $4,800 to $5,400 for an overlay, given the average cost to replace a shingle roof is $8,000 to $9,000. Of course, the exact cost depends on how much repair work is needed on the old roof.
Second Layer of Shingles vs. Roof Replacement
A tear-off is more advantageous than installing new shingles over an existing roof. The only issue is the cost. Unfortunately, a tear-off costs almost twice as much as a layover.
Meanwhile, a tear-off lasts longer than a layover and eliminates moisture and heat issues common with roof layovers. Also, you can capitalize on emerging roofing trends and technologies when installing a new roof. Above all, a newly installed roof is easier to maintain than a layover.
How Many Layers of Shingles Can You Put On Top of Each Other?
Most states permit two shingle layers at most. You must install a new roof if you encounter leaks or other roof issues after installing the second layer of shingles.
However, we occasionally see a few roofs with three or four layers of shingles, and some look perfectly fine. So, it comes down to what your local codes say and whether you’re comfortable with the consequences of an additional layer of shingles.
Can I Put Three Layers of Shingles on a Roof?
Yes, you can install three shingle layers on a single roof. Though uncommon and not permitted by most building codes, some homeowners do it in certain circumstances.
Again, it’s more convenient than tearing down the existing shingles and installing a fresh roof. Also, it’s less costly and requires fewer materials. However, the challenges are endless.
For instance, imagine the effort it takes to reach the roof decking! It’s easier to give up on the repairs than dig through the three roof layers to reach the deck.
Similarly, three shingle layers on a single roof cause major heat and moisture issues as each additional shingle and underlayment layer traps more heat and moisture. Finally, the shingles put extra weight on the roof structure, increasing the risk of a cave-in.
Can I Put Four Layers of Shingles on a Roof?
Yes, in some states, you can put four shingles layers on a single roof. However, you should first check with your local building authority, as most states permit a maximum of two shingle layers.
More importantly, even if your state permits it, we strongly advise against putting four shingle layers on your roof. It puts too much weight on the roof and the building, occasionally causing foundation shifting. In addition, the extra moisture and heat trapped between the shingles decrease energy bills and can quickly ruin the roof.
FAQs
Are two shingle layers better than one?
No. Two shingle layers aren’t better than one. First, two shingle layers trap heat, accelerating roof damage and shortening its lifespan. Moreover, the trapped heat can cause a warmer home, potentially increasing cooling bills in the summer. Finally, maintenance is a nightmare with two shingle layers on the roof.
How do you start the second layer of shingles?
To start the second layer of shingles, use a starter strip or cut pieces to initiate a second course. Rip-cut the starter strips to butt up against the second course of the old shingles. Additionally, ensure they are even with the front of the existing roof. Nail the starter shingles along the top edge, then proceed to the second course.
How long does the second layer of shingles last?
The second layer of shingles lasts 16 years on average, nine years less than a single layer of shingles. Why? Because of heat, moisture, and maintenance challenges. The second layer of shingles traps moisture and heat, causing faster roof deterioration. Worse still, repairing the old shingles and decking or sheathing below takes a lot of work.
Can you put a second layer of shingles over architectural shingles?
Yes, you can install a new layer over existing architectural shingles. Indeed, you can install up to four architectural shingle layers on one roof in some states. However, the consequences are monumental. For instance, the extra heat, moisture, and weight cause faster deterioration and shorter roof life.
Summary
Putting new shingles over an old one is a good way to cut reroofing time and costs. It also requires fewer materials. However, the installation process is a complex job that requires a professional. More importantly, a roof overlay puts extra weight on the roof and worsens the home’s moisture and heat issues.