Usually, we like to get some sort of guarantee that this roof will last at least 5 years or so. In reality, it does not work like that. It is safer for the buyer and seller to think in terms of functionality, how much life is left. This can have six categories.
Appeared to be in the first half of its useful life.
Appeared to be at the midpoint of its useful life.
Appeared to be in the second half of its useful life.
Appeared to be nearing the end of its useful life.
Appeared to be at the end of its useful life.
Appeared to be past the end of its useful life.
Second, no one can say exactly what the age of the roof is. Sometimes shingles are sitting in the warehouse for 2 or 3 years even before they are put on a roof. Also, manufacturers because of the fluctuations in the oil prices, sometimes use lower quality materials. The local weather plays a MAJOR role too. So, you can only go on what appears to be the case.
Let's take two examples, a house in a very windy place, had a roof put on five years ago. However, because of the wind the roof looks terrible, even though it had high-quality shingles. On the other hand, you have another house, in a place with great weather, the roof has been on this property for 10 years, and it has no signs of "wear and tear", even though it had standard shingles.
The demarcation of a failing roof is the loss of shingle granules. That's the beginning of the end. Where do the granules end up? In the gutters. Take a Look at the gutters if you see a lot of granules, you can be pretty sure the home inspector is going to see a lot of issues. Also, another test is to take a single and bend it 2 inches, if it cracks, it's a sign of "end of life", if the shingle is flexible, the roof is good.
You also make a guess, like this, most roofs are going to last 10-15 years. Years 1 - 3 the Roof looks relatively new, years 4-7 the sealant gets bad, granule loss takes place. years 7-10 shingles start to coming off, 11-15 shingles start to come off, leaks take place. This is just a very general idea. I would recommend to add - 3 years at least to the age of the roof. As always it is safer to estimate more.
So when you get a roofing certificate, it's only a guess. There is no way to be sure. One bad storm can take away the whole life of a roof sometimes.
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