Every February we get calls from Olathe homeowners with a stain spreading across an upstairs ceiling, usually along an exterior wall, usually on a north-facing slope, on a roof that has never leaked in a rainstorm. That is an ice dam, and it is a heat problem rather than a roof problem.
The mechanism
Heat escapes from the living space into the attic and warms the underside of the roof deck. The snow lying on the upper part of the roof melts. The meltwater runs down to the eave, which overhangs unheated space and sits at outside temperature, and refreezes into a ridge of ice. Each cycle grows the ridge. Water now pools behind it and — because a shingle roof is designed to shed water running downhill, not to be submerged — it works sideways and upward under the courses and through the deck.
The rule most older Olathe roofs were built without
The 2018 International Residential Code, which the City of Olathe enforces, requires an ice barrier at the eaves: either two layers of underlayment cemented together or a self-adhering polymer-modified bitumen membrane, running from the lowest edge of the roof to a point 24 inches inside the exterior wall line, or 36 inches on steeper pitches.
That membrane is the last line of defence when water backs up. The trouble is twofold. Plenty of Olathe roofs installed before the mid-2000s have no ice barrier at all. And because Olathe does not inspect residential reroofing, a shortcut here is never caught — we regularly find a single three-foot strip along the eave whose upper edge stops outside the wall line, which is precisely where it does no good, because the water gets past it and into the wall cavity.
Fixing it properly, in order
- Air-seal the attic floor. Recessed lights, the attic hatch, plumbing stacks, top plates, and above all bath and kitchen fans that terminate in the attic instead of outside. This is the highest-value work and it lowers your heating bill at the same time.
- Insulate to depth. Most Johnson County attics we open are short of current recommendations, often by half.
- Balance the ventilation. Continuous soffit intake with baffles keeping insulation out of the airway, and a ridge vent to exhaust. Cold attic, cold deck, no melt.
- Install the ice barrier properly at the next reroof. Full self-adhering membrane from eave to well past the wall line, in all valleys and around penetrations. On low slopes and problem north faces we run it further than the code minimum.
- Heat cable last. A management tool for geometry that genuinely cannot be fixed — a dead valley, a long low-slope run over unheatable space — not a substitute for the four steps above.
If one has already formed
Do not chip at it. An axe or a hammer will destroy the shingles under the ice and turn a winter leak into a spring reroof. Do not put salt tablets in the gutter — they corrode aluminium and kill the planting below. Pull snow off the lower few feet of the roof with a roof rake from the ground, which removes the fuel, and get the ice steamed out by someone with the right equipment. Then fix the attic before next winter.
Related questions
Is this covered by insurance?
The resulting water damage often is; the underlying cause usually is not. Most policies cover sudden and accidental water damage from ice damming - the ruined drywall, insulation and flooring - while excluding the work needed to prevent it recurring, which is treated as maintenance. Read your policy, document the damage, and expect to pay for the insulation and ventilation fix yourself.
Why does only one side of my roof get them?
North-facing slopes get far less winter sun, so snow lingers and the freeze-thaw cycle runs longer. Add any local heat source below - an unsealed bath fan, a poorly insulated cathedral ceiling, a bathroom under that slope - and that is where the dam forms. It is almost always a heat map rather than a roof-material question.
My gutters get destroyed every winter. Same cause?
Yes. The weight of a dam plus icicles is enormous and pulls gutters off the fascia. Heavier hangers spaced closer help them survive, but the actual fix is upstream: stop the dam forming and the gutters stop being torn off.