How a dam forms
Heat escaping into the attic warms the roof deck above the living space. Snow on that section melts and runs down to the eave, which sits over the unheated overhang and stays below freezing. The water refreezes into a ridge, and the meltwater behind it backs up under the shingles. Once it reaches past the ice barrier or where there is none, it comes into the wall.
Milford gets around 25 to 30 inches of snow in a normal winter, with freeze-thaw cycles rather than a deep steady cold. That pattern is close to ideal for dam formation. The 1950s capes with finished attics and knee walls are the worst cases because the insulation is thin and the warm space sits directly against the roof.
Reading the damage
Inside, the signs are a stain or peeling paint at the top of an exterior wall, a wet spot near a window head, or a soffit dripping in February. On the roof, the first few courses at the eave curl, granules wash out, and the deck under them goes soft. Gutters pull away under the weight of the ice.
Three fixes, in order of value
Air sealing comes first. Recessed lights, the attic hatch, plumbing chases and top plates leak warm air into the attic far faster than insulation alone can offset. Sealing them is cheap and has the biggest effect.
Insulation second. Connecticut's current code calls for roughly R-49 in the attic; many older Milford houses have R-11 to R-19. Adding blown cellulose or fiberglass over the existing layer, with baffles at the eaves to keep the soffits open, brings the deck temperature down.
Ventilation third. A continuous ridge vent paired with open soffit vents moves outside air across the underside of the deck so it stays close to the outdoor temperature. Gable vents alone do not do this. The 1-to-300 ratio of net free area to attic floor is the target, balanced between intake and exhaust.
What the roof itself needs
Ice and water barrier at every eave, extending at least 24 inches inside the warm wall line, is the code minimum and the last line of defense. On a house with a 2 foot overhang that means 4 feet or more of barrier up the slope. Valleys and low-pitch sections get full coverage. On a re-roof this is standard; on an existing roof with dam damage, the bottom courses are stripped and the barrier retrofitted.
Heat cables and other half-measures
Self-regulating heat cables along the eave keep a channel open and can protect a problem area until the attic is fixed. They use electricity all winter and do nothing about the cause. Raking snow off the bottom 3 feet of the roof after each storm also helps, and is safer done from the ground with a long-handled roof rake. Neither replaces the insulation and ventilation work.