The operative word here is remediation. This isn't a new install, so I'm looking at how to strategically work with what I've got.
The previous owner put a new shingle roof on my garage about 4 years ago, but the problem is that the roof wasn't sloped enough for shingles. Most of the water runs off OK, but some does get through the shingles toward the back. I'm trying to find a good solution that ultimately just needs to prevent this leaking. I'm mostly concerned about cost and hassle. For right now I just have a tarp over the shingles. I'd like to avoid removing the shingles if possible. At this point I'm looking at the following options...
A.) Any solution that would allow me to "patch" or seal the problematic area of shingles, making them less permeable where the pitch is so low that water gets through?
B.) A solution along the lines of removing existing shingles, adding improved waterproofing underpayment, and re-installing existing shingles.
C.) Any overlaying solution that would allow me to avoid ripping off the shingles. For instance, maybe metal or polycarbonate over shingles.
D.) If no good options between A, B, and C, then I'm looking at my material and method options for all out re-roofing. In particular, considering cost, difficulty, one-man-job or not, continuous or piecemeal install, rental equipment, etc.
I'm looking for a good DIY path forward, including any overlooked options and/or particular insights from someone fixing a similar problem.
Bonus: Any alternative uses for relatively new shingles if they're removed?