Where new roof shingles meet old, how to fix poor seal?

Question

So about 6 years ago we had all the shingles in our house replaced. Last year we added on a room to the house, and luckily they were able to find and use the same shingles on the addition. However, I found a where the new shingles meet the old; some of the old shingles are not tightly laying on the new ones – not forming a tight seal. How do you recommend I make these new shingles flush with the old one? If using cement or such where on the old shingle would I place it? E.g. very bottom or 3 inches from the bottom etc.?

I also want to point out that the new shingles look perfectly placed and proper with the old ones as far as placement goes, the seal just seems off.

Answer 1

Get a caulking tube of asphalt flashing cement at the hardware store and put a 1/8-3/16 inch bead of it under each tab. Use good judgement, and leave enough space at the shingle edges so that the cement doesn't squeeze out.