When contemplating a new roof, many people hope to simply do a shingle over and avoid the extra expense and mess of tearing off the existing roof and starting from scratch. Although that sounds like a good idea, I can assure you that the cons heavily outweigh the pros. In fact, the ONLY pros to a shingle over is the fact that it’s cheaper and cleaner. However, what if there is an unknown leak, or bad roof flashing? Will that get fixed or will that damaged wood be replaced during a shingle over? What if some of the roof decking has buckled and warped over the years, is that going to be noticed and fixed during a shingle over?
Apart from the problems that can go unnoticed during the actual shingle over, there are long term effects to consider as well. For instance, instead of just one roof on your home, you now basically have two. That’s a lot of extra weight, putting added stress on the roof decking and rafters. Also, two layers of shingles are going to attract a lot more heat than just one layer, which can lead to the shingles prematurely deteriorating. Also, what about all those black streaks “algae” growth and bacteria on the original layer of shingles? Now all of that is trapped under a 2nd layer of shingles, again having the potential to shorten the lifespan of the top layer of shingles. What about the length of nails used for the second layer, are they the right length? If they do not penetrate the wood roof decking properly than the only thing the new roof is nailed to is the old shingles, that’s not good at all. What about the simple fact that most shingle manufactures state that if their product is installed over an old roof than your warranty just got VOIDED! Now that is what you would call a bad day.
If you haven’t caught on by now, we are not fans of shingle overs at all. That is why we don’t recommend them, nor do we do them. Over the years, we’ve seen a ton of problems that can be caused by shingle overs. Does it cost more to tear off? Yes. However, by spending a little more now and doing it right, you can save yourself thousands of dollars and big headaches later.