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A Guide to Interlocking Asphalt Shingle Roofing: What You Need to Know

As homeowners, most of us are familiar with asphalt shingles. They have been successfully installed for decades, and most new homes still use them. Asphalt shingles have evolved over time to include a few configurations, including 3-tab, dimensional, architectural, and interlocking.

Three-tab, dimensional, and architectural shingles are designed and installed using basically the same method; however, interlocking shingles are very different.

These shingles were originally designed to reduce or prevent damage to a roof from high winds. This required completely changing the way a typical asphalt shingle is installed.

Today we will discuss what an interlocking asphalt shingle is, why they were used, and why they are no longer available.

What is an Interlocking Asphalt Shingle? 

Interlocking asphalt shingles were introduced a few decades ago. These shingles were completely different from previous fiberglass/asphalt shingles, roof tiles, and natural stone in use at the time.

Primarily marketed as the solution to strong wind damage, these shingles were designed to interconnect to each other on all four sides, as opposed to standard shingles that simply overlap. The general consensus was that this system of interlocking tabs would use the weight of the surrounding shingles to prevent the lifting of a single shingle in high wind areas.

Why Would I Want an Interlocking Shingle Roof?

These interlocking shingles were very popular in areas with high elevations, like the upper midwest region of the United States. At the time, three-tab shingles dominated the fiberglass/asphalt shingle industry, but they did have drawbacks. For instance, these shingles were relatively thin, making them vulnerable to lifting.

On this type of roof, if a single shingle got torn off by strong winds, a leak usually followed. Interlocking shingles were designed to solve this problem by essentially weaving shingles together without additional fasteners. These shingles often carried a better warranty than their three-tab counterparts, making them attractive to consumers in these areas of the country.

Why Would I Want to Avoid an Interlocking Shingle Roof?

Over time, interlocking asphalt shingles have been found to have vulnerabilities. So much so that production was stopped some years ago after the introduction of dimensional shingles. The problem with interlocking asphalt shingles comes down to the design.

Because these shingles interlock with adjacent shingles in all four directions, there was inevitably air trapped beneath the shingle, causing a pucker. This meant that the puckered area of the shingle would not lay perfectly flat and thus had no support from the roof decking. Ironically, this caused a worse problem than the one the shingle was designed to correct.

The most common issue with interlocking asphalt shingles is that they were very susceptible to damage from hail and other falling debris. The shingles were originally fairly thick, which gave them better resistance to impacts. However, as the shingles became more popular, manufacturers began making the shingles from thinner materials. This made the shingles easier to install and weave together, but it also greatly reduced the shingle’s ability to resist damage from hail, which tends to accompany high winds.

Are Interlocking Asphalt Shingle Roofs Bad?

Most roofing experts share the opinion that the design of interlocking asphalt shingles was based on a good idea. At the time, the roofing industry was still using decades old technology, so the concept of tying each shingle to its neighbor seemed to solve inherent weaknesses found in three tab shingles.

The problem this design attempted to solve was that standard shingles were very vulnerable to strong winds and impacts. Because three tab shingles were quite thin and light, the built-in adhesive strip was not always strong enough to keep the shingle flat on the roof deck. This thin nature would often cause the shingle to fold upon itself in windy conditions, often breaking the shingle. Obviously, this caused moisture problems, but at the time other roofing options were sparse.

When the interlocking design was introduced, it appeared to solve many of the inherent concerns surrounding regular three tab shingles. In practice, however, this was not always the case. Interlocking shingles required very specific installation, so many roofing professionals were required to undergo training just to be authorized to install and warranty them.

Unfortunately however, even when the shingles were perfectly installed, the system was actually more vulnerable to hail and other damaging debris than what it was attempting to replace. This led to lawsuits and the eventual discontinuation of the design.

Is Hail a Problem For My Interlocking Shingle Roof?

Yes. As mentioned earlier, the design of these shingles often caused air to be trapped under the shingles. Three tab fiberglass/asphalt shingles are relatively thin, so they must have solid support to withstand impacts from hail or other falling objects.

Where small hail stones would often bounce off of a three tab shingle (which was often the same thickness as interlocking shingles), interlocking shingles tended to absorb the impact due to lack of support from the roof decking. If these shingles suffered damage, the shingles ability to interlock with the surrounding shingles was often compromised. 

This essentially negated the solution the shingle was designed to provide, because it severely shortened the useful life of the entire roof.

If I Have an Interlocking Shingle Roof Should I Have It Replaced?

Most professional roofing companies suggest having the roof inspected by a qualified roof inspector. These are often insurance company adjusters, licensed home inspectors, or other roofing experts. In most cases, the inspector will look for storm damage or other natural occurrences that could have compromised the roof. Because these shingles cannot typically be replaced due to the lack of materials, if the insurance company covers the damage it will usually result in an entirely new roof.

However, that does not mean an interlocking shingle roof automatically needs replacing. Many installations are reaching their intended lifespan, but are still in good condition and functioning properly.

Most experts agree that the best course of action is to have this type of roof inspected annually, especially in areas prone to inclement weather. Interlocking asphalt shingles tend to break in heavy winds as they age and become brittle, so having them inspected often will usually identify potential problems before water damage occurs.

If I Can Find Replacement Interlocking Asphalt Shingles, Can I Install Them Myself?

Generally speaking, it is not recommended for non-professionals to install interlocking asphalt shingles. Because these shingles are not installed like other fiberglass/asphalt versions, even those with roofing experience may struggle to install them.

Most roofing contractors required training from the manufacturer to install these shingles if they wanted to offer the warranty due to their complexity. These shingles were very dependent on installation methods and techniques, so they tended to be installed only by professionals with specific training.

What Replaced Interlocking Asphalt Shingles?

In most cases, interlocking asphalt shingles were replaced with dimensional shingles. The design of interlocking shingles addressed the problem of shingles being lifted by strong winds that would allow rain and snow to contact the roof decking.

Dimensional shingles were designed to solve this same issue, but they do not require specialized training to install effectively. Where interlocking asphalt shingles used the weight of the surrounding shingles to protect each other from lifting, dimensional shingles simply add more weight to each shingle.

Dimensional shingles are essentially a three-tab shingle with an additional layer of material on the area of the shingle not overlapped by the shingle above. This design puts the strength of the shingle where it is needed without affecting any surrounding shingles. This makes dimensional shingles easily replaceable in either large or small sections without the repair looking like a patch. 

Dimensional shingles have the added benefit of creating no pattern. In contrast to three-tab or interlocking shingles, dimensional shingles are not carbon copies of each other. Some shingles will look entirely different from another shingle in the same bundle. This makes them ideal for homes in need of a facelift. 

Dimensional shingles are usually installed randomly, so installers will often work from several bundles at a time. Because these shingles form no pattern, they tend to disguise small defects. Because dimensional shingles have a much more distinct texture than a three-tab, they look similar to a shake-style shingle. Many think this adds visual interest to older homes that would otherwise look dated.

What Should I Do If I Have Problems With My Interlocking Asphalt Shingle Roof?

Unfortunately, in the vast majority of situations the only solution is to replace the roof. Interlocking asphalt shingles are no longer manufactured, so the availability of replacement shingles is extremely sparse. Some companies claim to have small stockpiles of unused inventory, but most homeowners opt to just replace the entire roof with dimensional shingles.

Opinions vary on the best way to approach the replacement of interlocking shingles, but some roofing contractors suggest having the roof inspected. In some situations, if a home with this type of roof has been damaged by acts of God such as hail and strong winds, insurance companies will honor a claim.

This is good news for homeowners, because since these roofs cannot generally be repaired, often they are replaced with a completely different roof as part of a claim. However, this is certainly not the case with all insurance companies.

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