Should you remove old shingles before installing a new roof system?

To tear off old roofing or not to tear off? It is a question that you may ask yourself when thinking of ways to save money on your next new roof installation. There are several reasons why tearing off old roofing materials is generally in your best interest: rotted decking, rusted metal flashing, and compromised workmanship and manufacturers’ warranties.  We see roofers all over the state of Alabama installing new shingles directly on top of the old roof. In our experience, this is never a good roofing practice. In fact, it can cut the life span of your “new” roof in half.
From a drone’s eye view, your roof looks perfectly fine. It’s not missing any shingles, no algae or mold growth, and shingles appear flat. Yet, underneath that layer of smooth, supposedly well preserved shingles lurks something moist and unreliable: rotted decking. When shingles are nailed onto soft, rotted decking, the nails will eventually wiggle loose. And in time, the nails will rust and cause leaks. Also, rotted decking will often fail to support your weight if you have to perform light roof maintenance, like blowing off leaves or clearing branches. Furthermore, decking that is deteriorated can eventually sag, impeding the efficient flow of water off of your roof. Not good! Water needs to flow off of your roof as quickly as possible every time it rains.
Next, rusted flashing is another important reason you should consider tearing off your existing roof. Metal flashing protects chimneys, pipes, wall to shingle transitions, and more on your roof. Oftentimes, the flashing that you can see above the shingle line will appear well preserved because water flows more quickly down vertical surfaces than horizontal surfaces. A common example is 90 degree angle wall flashing that is used as a transition flashing between vertical exterior walls and adjoining roof. The flat lower half of wall flashing rests on the roof, while the vertical upper half attaches to the wall. Almost always, you can see the vertical part of wall flashing, while you cannot see horizontal flat portion as it is covered by shingles. Leaving old roofing on top of existing wall flashing risks concealing rusted, leak prone wall flashing. Base flashing on chimneys and pipes is another common problem area. As much of base flashing on chimneys and pipes is under shingles, you cannot know for certain if the flashing is in good shape without tearing off the existing layer of shingles.
Finally, tearing off old roofing materials is usually necessary to obtain workmanship and manufacturers’ warranties. Due to issues like rotted decking and rusted flashing mentioned above, many roofers will not provide a workmanship warranty for new roofs installed on top of existing roofs. Also, the first layer of shingles is often not completely flat, and will cause the second, newer layer to not adhere properly. Furthermore, most roofing product manufacturers will not guarantee their products when nailed over an existing layer of shingles. Aside from potential decking and flashing issues, mold and algae can pose a serious threat to the longevity and aesthetics of the new roofing material. This is because simply covering over an existing roof that has mold and algae will not kill the growth. All of the uncertainties concealed within and underneath the first layer of shingles is sufficient to void most warranties on a roof that is roofed over.
To conclude, tearing off old roofing materials is generally best due to the possibilities of bad decking, rusted flashing, and compromised workmanship and manufacturers’ warranties. Don’t be rash and try to save a little cash! Please consider these things when looking for a quality roof replacement that includes a tear off.

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