Why Your Roof Only Leaks During Heavy Rain

(Zenith Roofing — Serving Marietta, Roswell, Alpharetta & Milton)

If your roof only leaks during heavy rain, you’re dealing with one of the most common and misunderstood roofing issues. Homeowners often assume that if a leak only appears during severe storms, it isn’t serious. The truth is the opposite:
A leak that only shows up during heavy rain is usually a sign that something in the roof system has already failed — but only becomes obvious when water volume and wind pressure increase.

Here’s a clear breakdown of why this happens and what it really means for your home.

Heavy Rain Exposes Weak Points a Light Rain Never Will

A properly functioning roof should not leak under any amount of rainfall.
When leaks only show up during heavy downpours, it usually means:

• Water is finding small gaps that don’t get overwhelmed in light rain

• Wind-driven rain is being forced sideways or upward

• The system has a minor failure that only appears under pressure

• A drainage or flashing issue worsens when large amounts of water are present

Light rain won’t always reveal these problems — but heavy rain will.

The Most Common Reasons Roofs Leak Only During Heavy Rain

1. Wind-Driven Rain Working Under Shingles

During storms, wind pushes rain sideways or even upward across the roof.
This can force water up under:

• Lifted shingles

• Broken shingle seals

• Creased areas from previous windstorms

• Poorly nailed shingles

North Georgia wind bursts — especially in Alpharetta, Milton, and Roswell — frequently create this issue.

2. Failing Flashing Around Chimneys, Walls, or Valleys

Flashing is designed to redirect water, but when flashing is loose, corroded, or improperly installed, it becomes one of the most common leak sources.

Flashing leaks often appear:

• At the ceiling near walls

• Behind chimneys

• In roof valleys

• Where shingles meet siding

In regular rain, the volume is manageable.
In heavy rain, water overruns the weak spot and migrates inside.

3. Cracked or Shrinking Pipe Boots and Zipper Boots

Plumbing vent boots are a frequent failure point, especially in older roofs.

Common problems:

• The rubber collar splits

• UV exposure causes cracking

• Zipper boots weren’t installed correctly around electrical lines

• The flashing loosens over time

During light rain, only a small amount of moisture hits the area.
During heavy rain, water overwhelms the cracked boot and follows the pipe directly into the attic.

4. Clogged Gutters and Overflowing Water

When gutters are clogged, water pools and backs up under the shingles.
Heavy rain creates:

• Gutter overflow

• Water intrusion under the drip edge

• Saturation at the fascia and soffit

• Leaks that appear on exterior walls or ceilings near the eaves

Marietta and Roswell homes with heavy tree coverage see this problem constantly.

5. Improper Roof Pitch or Design Flaws

Some roof shapes naturally trap water or move water too slowly.

Examples:

• Low slopes with architectural shingles (not rated for low pitch)

• Dead valleys

• Roof-to-wall transitions without proper kickout flashing

• Wide dormer returns that push water sideways

Light rain drains.
Heavy rain overflows and leaks inside.

6. Old, Brittle, or Granule-Depleted Shingles

As shingles age, they lose:

• Flexibility

• Protective granules

• Water-shedding ability

When the asphalt surface becomes exposed, the roof absorbs water instead of shedding it.
During regular rain, the absorption may not exceed the threshold needed to create a leak.
During heavy rain, the roof becomes overwhelmed.

7. Attic Condensation Mistaken for a Leak

This is one many homeowners never consider.
During prolonged rainstorms, especially in cold-to-warm weather swings, condensation can form on cold roof decking.

This looks exactly like a roof leak but only happens:

• After long periods of rain

• When temperature swings are extreme

• When ventilation is poor

Homes with blocked soffits or undersized ridge vents are especially vulnerable.

Why This Happens So Often in North Georgia

North Georgia’s microclimate makes these leaks more common than in many other states.
Our region experiences:

• Rapid temperature swings

• High humidity

• Frequent wind bursts

• Heavy tree coverage

• Storm clusters with sideways rain

• Older neighborhoods with aging flashings and decking

Roofs here are exposed to conditions that push every weak spot to the limit.

When You Should Be Concerned

A roof that leaks during heavy rain is not “fine the rest of the time.”
It is already failing — the volume of water is simply the trigger.

You should schedule an inspection if:

• Water stains appear during storms

• You hear dripping in the attic

• Leaks occur only with sideways/wind-driven rain

• You see granules after storms

• Interior paint bubbles during heavy rain

• Your roof is over 12–15 years old

These are all signs of underlying damage.

What Zenith Roofing Looks For During an Inspection

Our inspections focus on identifying hidden failures, including:

• Wind-lifted shingles

• Failed seals

• Cracked pipe boots

• Zipper boots incorrectly installed near power lines

• Damaged flashing

• Saturated decking

• Gutter overflow points

• Storm-related bruising

• Ventilation problems

We document everything with photos and provide clear next steps.

Protect Your Home Before the Next Storm

A roof leak that only shows up during heavy rain is your roof telling you something is wrong.
The sooner it’s inspected, the easier it is to prevent bigger problems.

Zenith Roofing offers free, detailed inspections throughout Marietta, Roswell, Alpharetta & Milton, along with honest recommendations based on actual conditions.

If you’d like us to take a look, just reach out — we’re here to help keep your home protected year-round.