By Johnathan Mason, Ace Chimney Service.
Ice dams get blamed on gutters, but around here the chimney is often where the damage actually shows up. A masonry stack sits in a valley of snow, melts a ring around itself, and refreezes the water into a wedge that pries at flashing all winter. If you own an older home in Marengo, this is worth ten minutes of attention before the first hard freeze.
Why the chimney is an ice dam hot spot
A working chimney is warm, so the snow touching it melts first. That meltwater runs downslope, hits colder shingles near the eave, and freezes into a ridge that backs water up under the shingles and against the chimney flashing.
The chimney also interrupts the slope of the roof. Snow piles on the uphill side and sits there, which is exactly why homes without a cricket behind a wide chimney tend to see the worst of it.
Signs the ice is reaching your chimney
Look for stains on the ceiling or wall next to the chimney breast after a thaw, not during the storm. Other things worth checking:
- Icicles hanging directly off the chimney shoulders rather than the gutter line
- Damp or crumbling mortar on the attic side of the stack
- Rust streaks running down from the flashing onto the brick
- A musty smell in the attic that only appears in late winter
- Shingle tabs lifted or curled on the uphill side of the chimney
What to do before the freeze
The fall work is simple: make sure water has nowhere to sit and nowhere to soak in. That means sound flashing, a crown without open cracks, and a cap that keeps snow out of the flue.
A crown with hairline cracks will survive a rain. It will not survive water freezing inside those cracks forty times over a winter. The same goes for spalling brick, where trapped moisture pops the face off in sheets. Our chimney cap and crown work is aimed squarely at keeping that water out before it becomes a structural problem.
What not to do
Do not chip at ice against masonry with a hammer or a spade. You will take mortar and brick face off with the ice, and the repair costs far more than the dam would have.
Salt products sitting on the roof are also a poor idea near masonry, since the runoff accelerates spalling. If a dam is already causing an active leak, the safest short-term move is steam removal by a roofing contractor, then masonry repairs once things dry out in spring.
Marengo specifics
A lot of the housing here is older farmhouse and early-century masonry with tall, exposed chimneys and relatively little attic insulation by modern standards [Observed]. Tall stacks catch more wind and more snow, and warm attics melt snow faster, so both halves of the ice dam recipe are common in this part of McHenry County.
If your chimney has not been looked at from the roof in a few years, that is the piece homeowners skip. A chimney inspection covers the crown, flashing, cap, and mortar joints, and it is the cheapest winter insurance there is. You can also work through the basics yourself first using our DIY chimney care guide.
Getting ahead of it
We have been repairing chimneys in Crystal Lake and across McHenry County for 29 years, we are insured and bonded, and we quote the price up front. We are out seven days a week, 7 AM to 7 PM. Call (815) 320-0883 and we can get on the roof before the snow makes that harder.
Frequently asked questions
Does more attic insulation stop ice dams?
It helps a great deal, because a colder roof deck melts less snow. Air sealing the attic floor matters just as much as insulation depth.
Will a chimney cricket fix the problem?
A cricket sheds snow and water around a wide chimney instead of letting it pile against the back wall. It is the standard fix on stacks wider than about 30 inches.
Can ice actually damage the flue itself?
Yes, indirectly. Water that soaks into a masonry chimney freezes inside clay tile joints and mortar, which is a common cause of cracked liners.
My leak only shows up in February. Is the chimney the cause?
A leak that appears in a thaw and not in a summer thunderstorm points strongly at ice, since a driving rain would find a simple flashing gap year round.
Should I run heat cables on the roof?
They can manage an isolated problem area, but they treat the symptom. Insulation and air sealing address the cause and cost nothing to run.
Can I burn fires normally during an ice dam?
Usually yes, as long as the flue itself is sound. If water is entering the firebox or you see damp soot, stop burning until it is inspected.
Is spring or fall the better time for masonry repair?
Fall, before freezing weather. Mortar needs above-freezing temperatures to cure properly, so late-season work often has to wait until spring.
Do you inspect the flashing as part of a normal visit?
Yes. Flashing, crown, cap, and mortar all get looked at, and we show you photos of anything we find rather than just describing it.
Published October 20, 2026.