Stand in the yard and sight down the length of your gutter the way you would sight down a board at the lumber yard. It should read as a straight line, dropping very slightly toward the downspout. What most people see instead is a shallow smile: high at both ends, dipping somewhere in the middle, sometimes with a visible gap between the back of the gutter and the fascia board where you can see daylight.
That gutter is not sagging because it is heavy. Empty aluminum gutter weighs less than a pound per foot. Even loaded with water it is not much of a load, and it certainly is not more than the house can hold. It is sagging because of how it was attached, and on a lot of CSRA homes that means one of two things.
Spikes and Ferrules, and Why They Let Go
For decades gutters were hung with a long nail driven through the front lip of the gutter, through a small metal sleeve called a ferrule, through the back of the gutter, and into the fascia board behind it. Spike and ferrule. It is simple, it is cheap, and it worked well enough that there are still thousands of houses around Augusta wearing it.
The problem is that a nail in wood is a friction fit, and everything about a gutter is designed to break friction. A gutter that grows and shrinks five eighths of an inch across a hot day is working each spike back and forth in its hole a fraction at a time. Add fascia wood that swells when it is damp and shrinks when it dries, and eventually the hole is bigger than the nail. Once one spike backs out, the two beside it carry more load and back out faster. That is why sagging gutters get worse quickly after looking fine for years.
Hidden hangers changed this. A hidden hanger is a bracket that clips over the front lip of the gutter and hooks the back edge, and it fastens with a screw rather than a nail. Screws hold in wood under cyclic load in a way nails do not. The hanger sits down inside the gutter so you cannot see it from the ground, which is where the name comes from, and it spreads the load across the gutter profile rather than pinching it at two points the way a spike does. If your gutter has a row of nail heads visible along the front face, you have the old system. If the face is clean, you have hangers.
Spacing Is the Other Half of It
Getting the hardware right does not help if there is not enough of it. Common practice is a hanger every 24 inches, tightening to 18 inches or less in areas that see real weather load. In the CSRA the argument for tighter spacing is not snow, it is volume. An inch of rain falling in forty minutes, which happens repeatedly here between May and September, briefly fills a gutter to the top. Water weighs a little over eight pounds a gallon, and a full five-inch K-style gutter holds roughly a gallon and a quarter per running foot. That is about ten pounds a foot for the length of the storm.
Twenty feet of that between two widely spaced hangers is two hundred pounds hanging on very little. It does not fail all at once. It takes a set, the way a shelf takes a set, and then the low spot it just created holds water permanently, which means that section is now loaded all the time instead of during storms. The dip deepens itself. This is why a gutter with standing water in the middle is not a cosmetic complaint, it is a progress report.
Another thing worth checking: what the hangers are screwed into. A hanger screw needs to land in solid fascia. If the fascia board is soft from years of the roof edge dripping behind the gutter, the screw threads have nothing to bite. You can put in twice as many hangers and they will all pull out together, because the wood is the weak link, not the hardware. Somebody who tells you they can straighten your gutters without looking at the fascia behind them is guessing.
What This Looks Like From the Ground
You do not need a ladder to catch most of this. A gutter visibly separated from the fascia, a run that dips in the middle, water sheeting over the front edge during a storm while the downspout barely runs, or a gutter that has rotated so the front lip sits high are all the same story told different ways. So is a downspout that has pulled loose at the top, because that is usually the gutter moving, not the downspout.
The fix depends on how far it has gone. A gutter that has sagged but not deformed can often be re-hung, which means pulling the old spikes, adding hidden hangers at proper spacing, resetting the pitch, and dealing with whatever the fascia is doing. That is a real repair and it buys a lot of years. A gutter that has sat full of water long enough to stretch and oil-can along its bottom has changed shape permanently, and no amount of re-hanging makes it hold a line again.