Q&A – Is it Normal for my Roof’s Seam to Have a Bulge?

This Texas homeowner wanted to know if a bulge they found on their roof’s seam was standard. 

Jason, a homeowner in Texas, noticed a bulge at the seam of his roof while remodeling his home. Wanting to know if this was normal, he asked: 

I am in the middle of a remodel and addition. We are basically adding a rectangular building to the back of the existing house to form a "T" shape. The shingles were just installed on the addition and tied into the existing shingles. There is a bulge at the seam where the new shingles meet the old shingles. The roofer is telling us that this is standard. Is that true? 

Mike from Texas Traditions Roofing had to say in response to Jason’s question: 

Hello Jason. Thanks for reaching out to us. It’s always tough when you’re tying a new roof into an existing roof. The bulge could be they didn’t remove the existing shingles and laid the new shingles on top of it and tied in. It could be the new shingles are thinner than the old shingles and it doesn’t lay smooth or they come together.  

From the pictures I don't see anything I wouldn't expect to see in a closed valley installation. The shingles at the lower arrow is not going to be as smooth as the main field because the shingles forming the valley terminate under the shingles to the right of the valley. The shingles at the upper arrow is where they had to tie in the new shingles to the old shingles. That area can be rough because they have to lift up the old shingles and get underlayment underneath to tie in the new addition to the old addition. That can bend the old shingles and creating a rough look. It's difficult tying a new roof into an old roof and having the old roof transition smoothly to the new section. 

Marty Stout from Go Roof Tune Up said: 

Congratulations on getting a nice room addition to your existing house. 

Any time you connect anything old to anything new you have the possibility of it not looking perfect. What the photos show could be caused by the substrate, plywood, not making a smooth transition from old to new. Or it could be that the Underlayment, paper under the shingles, is causing a “bulge” effect.  Whatever the cause, this will likely become much less noticeable after some time has gone by. This will not affect the longevity of the shingles and the longer you enjoy your new room the less you will look at it. 

The only thing that you can do at this point is have the entire roof on that side of your house removed and redone.  You won’t gain any benefit except to try to win the “Battle of the Budge.” 

Brad Beldon from Beldon Roofing Company says: 

Yes, it seems to be accurate. When opting for a closed valley installation, you'll have multiple courses on one side. If the customer has any significant concerns, they can consider hiring a home inspector to ensure the installation is done correctly. I hope this information is helpful. 

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