Long Gutter Runs Move With the Weather in St. Louis

Walk a long gutter run at six in the morning in January, then again at three in the afternoon in July, and you will find the metal has changed length. Aluminum expands when it warms and contracts when it cools. A gutter that runs along the back of a house for 40 feet or more moves by a noticeable amount between a cold February morning and a sunny July afternoon. Nobody sees it happen, but the hangers, the end caps and the corners all feel it, season after season.

How much a run moves

Aluminum expands about 13 millionths of an inch per inch for each degree Fahrenheit of temperature change. That sounds small, but multiply it out. A 40-foot run is 480 inches long. If the metal warms by 80 degrees, it grows about half an inch from end to end. The sun-facing side of a south gutter can run well hotter than the air on a clear day, and the shaded north side of the same house may not follow the same curve. In St. Louis the swing between a winter night near zero and a summer afternoon in the nineties is wide enough that the metal never really stays put.

This matters because a seamless gutter has no factory joints along its length. The crew forms it on site from one coil, so the run is continuous from one end cap to the other. A continuous piece with no expansion joint has to be allowed to slide through its hangers, or the stress has to go somewhere else. The somewhere else is usually a corner, an end cap, or a hanger that is holding the whole run in one fixed position.

Fixed hangers and sliding hangers

There are two broad ways a crew holds a gutter. The first is a fixed spike and ferrule, where a spike goes through the hanger into the rafter tail or fascia and pins the gutter at that point. The second is a hidden or sliding hanger, a bracket that clips over the front of the gutter and lets the metal travel back and forth along the run. Both can be installed well. The real question is which one suits the length and sun exposure of the run in front of you.

A run held rigidly at every point has nowhere to go. On a long south-facing run in a hot summer, the metal tries to lengthen and pushes against the fixed points. The likely results are a bowed section between two hangers, a corner that works loose, or a gutter face that shows a faint wave in the afternoon light. Freeze and thaw cycles add to the load. Water that gets into a seam or behind a hanger freezes and expands in winter, and the same stress that had nowhere to go in summer can split a corner or pull an end cap off its bead. A gutter that sits perfectly straight on install day can end up with a sag that was never there at the start.

Where the stress goes first

The weak points are the places where the metal stops. End caps are the obvious one. The cap is sealed to the gutter with sealant and usually a rivet or screw, and when the gutter moves against a cap that does not move, the sealant takes the load. Outside and inside corners are the second place. A corner is where two runs meet at an angle, and each run can push or pull at the corner in a different direction. The third place is the downspout outlet, where the gutter meets a fixed piece of metal and the water exit is shaped to a hole.

None of this means a long run will fail. Many runs have held up for decades with the right hangers and a crew who understood the metal. It does mean the hanger type deserves a question before the work starts, not after the first winter.

What to ask before the crew starts

• Which hanger type will hold each run, and whether any of them are fixed at both ends.
• Where the longest runs have fixed points, and why each fixed point was placed where it is.
• Whether the hangers on the sun side of the house are sliding or fixed, and whether that differs from the shaded side.
• How the end caps and corners are sealed, and whether the sealant is rated for metal that moves.
• Whether the written scope lists the run lengths, so you can check the hanger count against them.

Ask for the answers in writing. A crew that can explain the hanger plan run by run has thought about the movement. A crew that answers with only a price per foot has not, and you will learn that in the first hard freeze.

Check it yourself on two mornings

You do not need tools to see whether a long run is free to move. Look at the gutter in the cold, first thing on a clear morning, then look again on a warm afternoon with the sun on that side of the house. Sight along the face from one end cap. A run that is fixed too rigidly will often show a small kink or bow at the midpoint between hangers, or a corner that looks slightly off square. A run with sliding hangers will look about the same both times. Check the corners and end caps too. A thin crack in the sealant, or a bead that has pulled away from the metal on one side, is an early sign that the run is working against something.

Do the same check on the shaded side of the house if you have one. The two sides can move by different amounts, so a run that sits well in the shade can still be tight on the sun side. If you see a difference, note which section it is, and take the photo from the same spot on both days so any change is easy to see.

What to do if the run already shows it

A bowed section or a split corner is not always a reason to replace the whole gutter. Often the fix is to change the hanger at the fixed point to a sliding type, reseal the end cap and corner with a sealant rated for movement, and check that the run still slopes toward the outlet after the change. If the metal has been stressed for years and has taken a permanent set, a section may need to be cut out and re-formed. That is a conversation to have with the crew who will do the work, before any metal is cut.

If you are not sure which situation you have, call Keys at (314) 220-2333 and ask the office to walk through the run lengths and hanger types with you. Ask for the photos and measurements to be written into the scope, so you have a record of what the gutter looked like before any change was made. That record is what you will want if a corner splits in February.