Get advice on how to check your roof for signs that it's time to replace, like curling and cracking shingles. Understand how layers of shingles wear faster than a single layer.
LESLIE: Mark in Hawaii needs some help with a roofing project. What’s the matter, Mark? You don’t want to look up at the beautiful sunshine?
MARK: (chuckles) Well, I just don’t want that liquid sunshine to come through my roof. (Tom and Leslie chuckle)
LESLIE: Well, tell us what’s going on.
MARK: Well, I bought the house maybe 10 years ago and I don’t know when the last time the composite shingles were replaced. They look like they’re about maybe three layers thick already and I’m wondering – is there any telltale signs  of when you should change the shingles and how many times can you overlay them before you have to strip them all the way down to bare wood?
TOM: Sure. Now, as a roofing shingle starts to wear, it dries up and the asphalt that’s in the shingle evaporates; the oils evaporate. What happens then, Mark, is the shingles start to curl and crack or they may just crack, depending on how old the shingles – the newer ones tend to just sort of fracture.
So, an easier way to do this is with a pair of binoculars. If you look carefully at the roof surface and you see some curling and deterioration or if you want to put a ladder up against the roof edge, that sometimes help because you can look straight down on it. When you see that sort of alligatoring and that cracking and that curling in the shingle, then it’s time to start thinking about replacing the roof.
Now, in terms of the layers, if you in fact do have three layers, I would not put a fourth one on. I would strip it all the way down to the original roof and just have a single layer . If you happen to have just one layer, you could put a second layer on but keep in mind that when you have multiple layers of roof , the newest layer doesn’t tend to last as long as if it was just a single layer. And the reason for that, Mark, is because the first layer holds a lot of heat and that will accelerate the deterioration of the new layer.
So, that’s what you want to do. Look for curling, look for cracking and if you’ve got to replace it and you’ve got three roofs, pull it off and start from scratch.