Seasonal

Summer Heat and Gutters: Expansion Joints and Sealant Failure

By Houston Gutter Repair Co. · September 27, 2026 · 7 min read

Summer's finally letting go. Houston just came through another stretch of 95-degree afternoons, and if a corner of your gutter started dripping in the last few weeks, the heat is why. Northern cities write about ice dams and heat cables; here the enemy is the opposite end of the thermometer. This is what three months of a roof edge at 140 degrees does to a gutter, and what to look for now that you can stand outside long enough to look.

Aluminum moves more than you'd think

Aluminum expands about 13 millionths of an inch per inch for every degree Fahrenheit. That sounds like nothing until you do the math on a Houston gutter. A 40-foot run is 480 inches. The roof edge on the west side of a house goes from about 45 degrees on a January night to 140 or more on an August afternoon — roughly a 100-degree swing. So that run grows and shrinks by about five-eighths of an inch between winter and summer, and by a quarter inch or more between dawn and mid-afternoon on a hot day.

The gutter is screwed to the fascia at every hanger. It can't slide, so the movement has to go somewhere. It goes into the corners, the end caps and the outlets — the only joints on a seamless system.

What that does to the sealant

Every corner is sealed with a bead of something. On a good install it's a polyurethane or a tripolymer gutter sealant that stays rubbery and stretches with the joint for a decade or more. On a cheap install it's silicone, or worse, a general-purpose caulk, and those go hard in UV and split after a few summers. Either way, a joint that has been stretched and squeezed a quarter inch a day for 90 days is tired by October.

The usual sequence by fall:

1. The corner seals fine in the cool of a March install.
2. Summer opens the joint a fraction each afternoon; the sealant works, but it's flexing at its limit.
3. A hairline gap opens on the sunny south or west corner, usually in late August.
4. The first October rain finds it. The porch is wet at one corner, and nobody's touched the gutter in months.

Which is why "my gutter started leaking and nothing changed" is such a common October complaint. Something did change: the sealant reached the end of its stretch.

Where heat damage shows up

• Corners and end caps on the south and west walls. The sun side fails first, often by years.
• Outlets. The hole cut for the downspout is sealed from inside the gutter, and the sealant there bakes in standing water on a badly pitched run.
• Long runs with no expansion joint. Runs over about 50 feet should have an expansion joint — a slip connection — in the middle. Many Houston homes don't, and on a 60-foot run across the back of a two-story in Katy that's nearly an inch of seasonal movement the corners have to absorb.
• Spike hangers. Heat cycles work the spikes loose in the fascia; each expansion pushes, each contraction pulls, and after a few thousand cycles the nail is a quarter inch out. This is half the reason spikes fail in Houston and hidden screw hangers don't.
• Painted finish. Baked-on factory finishes take the heat fine. Field-painted gutters — someone brushed a color onto old white aluminum — chalk and peel by the second summer.

How a gutter expansion joint works

A gutter expansion joint lets two halves of a long run slide past each other as the metal grows and shrinks. The common type is a slip joint: the ends overlap inside a fitted cover with a flexible seal, and each half is fixed to the fascia on its own side. The water still flows through; the movement goes into the joint instead of the corners.

It belongs near the middle of any run over about 50 feet, or where a long run meets a corner on a hot wall. On a run with a downspout at each end, the joint sits at the high point between them. Adding one to an existing seamless run means cutting the gutter, fitting the joint and resetting the pitch on both halves, which is a small repair rather than a replacement.

Resealing a corner yourself in the fall

On a single-story home, a corner reseal is a fair DIY job if you take your time.

1. Wait for two dry days in a row.
2. Scrape out all the old sealant with a putty knife.
3. Scrub the joint with a wire brush, then wipe it with rubbing alcohol.
4. Let it dry fully.
5. Work a bead of polyurethane gutter sealant into the seam from inside the gutter and smooth it with a gloved finger.
6. Leave it a day before any rain.

If the metal at the corner is cracked or thin, sealant won't hold; that corner needs replacing.

Heat and hangers

Hidden hangers are screwed through the back of the gutter into the fascia, and they hold even as the metal moves. Spikes are a friction fit, and every daily cycle loosens them a little. If you see spikes backing out after a hot summer, plan to swap them for screw hangers.

Why the sunny side fails first

The south and west walls get the longest, hottest sun, and the metal on those runs swings the most each day. Corners on those sides may need resealing years before the shaded north side. When you plan maintenance, start there. If only those corners leak, a targeted reseal is all the system needs.

Picking a sealant

Look for a product sold specifically for gutters, labeled polyurethane or tripolymer, and rated for metal and outdoor use. Avoid general-purpose acrylic caulk and plain silicone. Buy a fresh tube; old sealant that's been in the garage all summer may already be skinning over.

Sealant matters more here than the gutter does

Two gutters can be identical aluminum and one will leak at every corner in five years while the other goes fifteen. The difference is the bead. When a corner is resealed properly, the old sealant is scraped out, the aluminum is cleaned to bright metal, and a polyurethane gutter sealant is worked into the joint from inside on a dry day. Smearing new silicone over old, wet silicone — which is how a lot of DIY reseals get done — buys one summer.

A proper corner reseal is $150–$250 as part of a gutter repair visit, and it's one of the most common October gutter repairs in Houston. If more than a couple of corners are going and the system is 20 years old, repair vs. replacement is the honest conversation.

What to check this month

Now that it's cool enough to spend twenty minutes outside:

• Look under every corner and end cap for a dark streak on the fascia or a wet patch on the slab after a rain.
• Run the hose test from how to find a gutter leak on the south and west runs.
• Look at the front edge of each run for nail heads that have worked out over the summer.
• On any run longer than 50 feet, look for a corner that has pulled slightly open at the miter.
• Check that downspout elbows are still snapped together; they expand too, and a loose one drops off in the first cold front.

Why October is the month to fix it

October is on average Houston's driest month, the sealant cures properly in the dry air, and the crew isn't racing an afternoon storm. It's also the window before the November fronts and the December leaf drop. A corner resealed now goes into the wet season tight; the same corner left until January gets done between rains on wet metal, and it won't hold as long. Our end-of-season check next week covers the rest of the walk-around; the corners are the part the heat owns.