There’s a good dose of science in roofing. No, it’s not rocket science, and yes, it can be tricky, and that’s why you hire a trusted professional to do it for you. But while you’re not necessarily contemplating the trajectory of the hammer to correctly strike a nail to drive it in the most efficiently, you do need to have some understanding of how things like gravity and water work to design the best roofing system to keep your home or business safe and dry.
Take, for example, this downspout and valley combo:
You may ask: What’s wrong with this? Rain falls on the roof, gets funneled to the valley, to the gutter, and to your lawn. Except…
That’s not what’s going to happen here.
Look again: The valley will push rainwater into the wall/downspout area, which is then likely to back up and pond because it’s being stopped by the downspout blocking it on the roof and, potentially, leak where that puddle would form. Also, the downspout drops even more water from above (the gutter in another part of the roof) in the same area, which would just exacerbate the problem. There’s way too much water in this one spot on the roof! So to try to combat what was probably a pretty soggy spot, the wall has been caulked. It’s a natural reaction, but not the correct one.
But the good news is, this IS all fixable! (This is where calling a trained professional can save you some time, headaches, and probably some money.) To repair this spot, we would need to raise the downspout off the roof a few inches, so that the water (and any debris) from the valley can pass below it to the gutter, to be shuttled to a downspout. That’ll relieve the ponding, so the water from the valley has a place to go, and the raised downspout will send the water over a bigger area of the roof too. We would also want to replace the flashing behind the siding — caulk won’t hold up to the water in the area the way metal flashing will, to keep that spot in the wall dry and snug.