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Podcast: Every Layer Matters- Why Putting New Materials Over Old Materials Is a Bad Idea

Posted December 27, 2017 by Daniel White

In this episode, Daniel talks about some of the crazy re-roof problems he’s encountered when it comes to premature loss. Usually it has to do with mixing incompatible or old with new materials.

Podcast Transcription: RoofLifeB030-208

Shayla: Thank you for joining us today for the Roof Life of Oregon podcast. I’m talking with Daniel. Tell me about a roof that you saw recently that had shiplap with an architectural shingle, and what the problem is with that.

Daniel: Yeah, you know what? This is a great subject. When I first got there, he thought, the client thought he had only one or two leaks in the garage. And the roof is only seven years old and I thought, well, that’s odd for seven years old. It’s a straight roof, there’s no valleys, no weird penetrations- nothing. It’s odd for it to be leaking there. My second thought was, you know what? I bet the deck is bad. So I said, “Do you have attic access?” and he said, “yes, I do.”

So I went in the garage and I looked up inside and sure enough he has what’s called a shiplap deck. So we know what plywood is, we know what OSB is, large pieces. Shiplap can be different sizes and they’re actually independent boards. They’re almost like interlocking pieces, and there’s a gap that’s in them. This house is really old, and when that house was old those gaps were much, much smaller and tighter and the wood was good. Over time, as the house as aged, that wood has shrunk and as it shrunk, those gaps have gotten bigger. They’ve gotten harder. The knots are starting to crack out. If you read manufacturer’s installation instructions, they tell you, you cannot put an architectural shingle over an old shiplap deck, because it will leak.

So I climb up in there, I’m looking around the garage and he’s got a little hatch that goes into the rest of the house. And he goes, “Well, it’s not leaking in there.” I said, “Well, I’m going to go in, because I want to take a look.” And sure enough, I open up and he’s got another leak, another leak, another leak. And I went all the way back and the whole house is leaking everywhere. He had no idea.

And it’s because this shingle was put over the wrong kind of deck. Now he had done all of his research. He put a synthetic on there. He put a good quality shingle, but that doesn’t matter if it’s done correctly. The manufacturers tell you what you’re supposed do to with them and how to do it.

His other comment to me was, “Well, my old roof was an old three-tab and that thing was up there for twenty years and it never leaked over the shiplap.” That’s correct, because that type of shingle shed water better. Modern architectural shingles are built different. Their seams are close together. The water doesn’t just flow off of them. If the water gets stuck inside one of those seams, it turns up and underneath, that shiplap deck is unstable. It’s got those big gaps. It works on the nails and gets leak. When you have the three-tab, there’s great big gaps and the water’s able to shed off better. That’s why he wasn’t experiencing that problem with his old roof.

Modern shingles are different and if you read the manufacturer’s installations, they’ll say don’t do that. So unfortunately, this homeowner has a seven year old roof and I had to stand in his kitchen and tell him he needed a new roof, because we can’t fix this leak, because there are so many of them. We can’t fix it now, because if we try to take off a couple of shingles and fix this repair, it may just move the leak over a foot. It’s going to move it. And then you’re going to work another leak and then another leak. So when this roof is replaced, and it needs to be replaced, all the shingles have to come off. All that paper has to come off. And then I told him he needs to have a solid deck put down. Either plywood or OSB needs to go down over the top. The shiplap can stay there, but you need to put a solid deck over the top of that, then put the new roof on. So you just can’t do repairs on a roof like that, because we’re just going to keep moving the leaks.

Shayla: Alright, so if you’re listening and you have any questions about anything Daniel talked about today, reach out to the team at Roof Life of Oregon.

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