Insulation Guide

Ice Dams: What Causes Them, How to Prevent Them, What Not to Do

An ice dam is a ridge of ice along the edge of a roof that stops melting snow from draining off. It forms when heat from the house keeps the upper roof above freezing while the eaves stay below freezing: snow melts high on the roof, runs down and refreezes at the cold edge, and the water that pools behind the ice can work up under the shingles and into the attic, walls and ceilings. The lasting fix comes in a set order: seal the air leaks from the rooms into the attic, insulate the attic floor to at least code depth with full depth carried out over the outside walls, and keep cold outside air moving from the soffits to the ridge behind baffles.

The University of Minnesota Extension says the heat primarily comes from the house, and only in rare instances from the sun, and that in many homes the main route for it is warm air leaking into the attic. So an ice dam shows up on the roof, but the cause is usually in the attic.

What causes ice dams

Ice dam formation takes three things at once, the Department of Energy’s Building America Solution Center says: snow on the roof, a poorly air sealed or poorly insulated attic, and freezing temperatures. It adds that an ice dam can form with as little as 2 inches of snow on a roof. The University of Minnesota Extension puts the temperatures precisely: the higher parts of the roof surface above 32°F while the lower parts are below it, as averages over sustained periods, with the outside air below freezing. Warm air escaping into the attic heats the underside of the roof deck and melts the snow above it. The meltwater runs down to the eaves, which hang out past the heated walls, and refreezes there. As more water arrives the ridge of ice grows and holds a pool of water behind it, and that water can be drawn up beneath the shingles.

The heat comes from a short list of places:

  • Air leaks into the attic. The Solution Center’s list of common leak points: gaps around wiring, light fixtures and especially recessed cans, plumbing stacks, furnace flues and chimneys, attic hatches and stairs, dropped ceilings, open soffits, exhaust fan housings, the top plates of the walls, ceiling drywall seams and attic knee walls. The University of Minnesota Extension calls air leakage the major mode of heat transfer behind ice dams in many homes.
  • Thin insulation at the eaves. Where the roof comes down over the outside walls there is little room for insulation, and the Solution Center notes that insulation there may be compressed or insufficient, which can leave warm spots on the roof deck that feed snow melt.
  • Heat sources in the attic. Leaky or poorly insulated heating ducts, heating equipment in the attic, and a chimney carrying heat from a well-used wood stove or fireplace all warm the attic. The Solution Center’s advice is to keep mechanical systems out of the attic and in conditioned space.
  • Recessed lights. ENERGY STAR says can lights draw warm air up into the attic in winter, and that the leaking air, plus the heat from older fixtures, can melt roof snow into ice dams, more likely when the can is close to the roof deck.
  • Exhaust fans. A bath or kitchen fan that empties into the attic dumps warm, moist house air right under the roof deck. The residential code in New Jersey, New York and Connecticut says air shall not be exhausted into an attic, soffit, ridge vent or crawl space. The University of Minnesota Extension adds that exhausts ending just above the roof can melt snow too.

The sun plays a part. Building Science Corporation’s Joseph Lstiburek says sun melt on its own usually makes only small icicles that don’t back water up, while his colleague John Straube notes that sun melt can still build an ice dam on a well-built roof, which is one reason BSC recommends a self-sealing waterproof layer at the eaves of sloped roofs. Bare patches in the roof snow are a different signal. North Dakota State University Extension says the snow on a house should look like the snow on an unheated, detached garage, with only a little melt around the edges, and that bare spots mean warm air is leaking from the living area and warming the roof.

How to prevent ice dams: seal, insulate, ventilate

The order matters. The Department of Energy’s Building America brief on preventing ice dams in vented attics gives three steps: construct an airtight ceiling plane, limiting the holes through the ceiling and air sealing every one; insulate well, especially over the top plates; and vent the underside of the roof deck. The Solution Center calls sealing the air leaks from the house into the attic the most important step. ENERGY STAR’s version is shorter: combined with attic insulation, air sealing can help to alleviate the formation of dangerous ice dams.

1. Seal the attic floor first

Air sealing is done with the old insulation pulled back, before anything new goes down, because fiberglass and cellulose don’t stop air. The Department of Energy’s guide warns that adding insulation without air sealing the attic risks serious moisture problems. The work is finding and closing every path from the rooms into the attic:

  • Top plates. The tops of the walls, where the ceiling drywall meets the framing. Building Science Corporation’s way of putting it: exterior walls are like chimneys, and you don’t want to vent the tops of them into your roof. The energy code in all three states requires the junction of the top plate and the top of exterior walls to be sealed.
  • Chases and bypasses. Open shafts beside chimneys, plumbing stacks and ductwork, dropped soffits over kitchen cabinets, and the open joist bays under knee walls. The Department of Energy’s job aid for sealing attic top plates matches the material to the gap: caulk up to a quarter inch, one-part foam or mastic from a quarter inch to 2 inches, two-part foam from 2 to 3 inches, and for anything larger a rigid material that won’t bend, sag or move, with support across spans wider than 24 inches.
  • Chimneys and flues. The residential code in all three states requires the space around a masonry chimney where it passes through floors and ceilings to be fireblocked with noncombustible material, and ENERGY STAR’s do-it-yourself guide says not to use spray foam there. The DOE’s weatherization job aid for chimneys and flues closes that gap with sheet metal and high-temperature caulk, and before new insulation goes in it sets a fixed dam around the flue at least 2 inches higher than the final insulation, keeping all combustible materials at least 3 inches away, or the clearance the local building official specifies.
  • Recessed lights. ENERGY STAR’s do-it-yourself guide says recessed lights can be sealed, but that it is difficult and can create a hazard if not done properly with non-combustible materials, and that it is best to consult a professional. It also says to keep all insulation 3 inches from can lights except those rated IC, for insulation contact. For new fixtures, the energy code requires recessed lights in an insulated ceiling to be IC-rated, labeled for no more than 2.0 cfm of air leakage, and sealed to the ceiling with a gasket or caulk.
  • The attic hatch or pull-down stairs. The energy code calls for access openings and drop-down stairs to an unconditioned attic to be sealed, and for attic hatches and doors to be insulated.
  • Exhaust fans. Bath and kitchen fans ducted all the way outdoors, with the fan housing sealed to the ceiling.

A few things stop the job before it starts. The Department of Energy’s guide says not to air seal or insulate an attic while the roof leaks, while active knob-and-tube wiring is in place, while an exhaust fan vents into the attic, while the house has an unvented kerosene heater or gas fireplace, or where the attic holds vermiculite. The roof leak is the roofer’s to fix first and the old wiring the electrician’s. Vermiculite is left alone: the EPA says to assume it contains asbestos and leave it undisturbed, without relying on a test to clear it. And because a tighter house changes how air moves through it, the DOE guide says chimneys and all combustion appliances should be tested before the work begins and again when it is done.

2. Insulate to at least code depth, and carry it over the outside walls

Once the floor is sealed, insulation slows the heat that conducts through the ceiling. The energy code’s ceiling table sets the minimum for new work:

  • New Jersey: R-49 in both of the state’s climate zones under the 2024 energy subcode.
  • New York: R-49 in climate zones 4, 5 and 6 under the 2025 Energy Conservation Construction Code, the zones that take in Westchester, Long Island and the Hudson Valley.
  • Connecticut: R-60 under the 2021 IECC in the 2022 Connecticut State Building Code. The next state code was expected to take effect on July 1, 2026, and has been delayed.

For an existing attic, the recommendations run higher than the New Jersey and New York code and match Connecticut’s. In every climate zone we work in, ENERGY STAR recommends R-60 for an uninsulated attic, or R-49 added on top of 3 to 4 inches already there, and the Solution Center recommends R-60 or greater for vented attics in climate zone 5 and colder.

Each state’s code accepts one step less, R-38 where R-49 is required or R-49 where R-60 is, when that full, uncompressed depth covers the whole ceiling and extends over the wall top plates at the eaves. That clause and the ice dam advice point at the same spot. The Solution Center recommends that, at a minimum, the insulation over the top plates should exceed the R-value of the exterior walls. The trouble is room: in a typical attic the rafters meet the floor at a tight angle, and the DOE guide says recommended R-values often cannot be reached there with fiber insulation. It says a contractor may suggest spray foam around the perimeter, for its high R-value per inch and its air seal, once vent baffles are installed in each rafter bay. Closed cell foam runs R-6.9 to R-7.1 per inch, the most R-value for the few inches available. Blown cellulose or fiberglass then brings the rest of the floor to depth.

Blown insulation settles. The code rates it by the manufacturer’s settled R-value, but it is blown deeper than that, to the bag’s minimum initial installed thickness, which is the number the code wants written on the depth markers in the attic. Right after the job, check the installed thickness against the markers, or against the bag’s installed thickness if there are none; in an older attic, compare against the settled thickness on the coverage chart. Our attic insulation guide has the inches by material.

3. Keep cold air moving from the soffits to the ridge

Ventilation is the third step, not the first. Its job is to carry off the little heat that still gets through a sealed, insulated ceiling and keep the roof deck cold. Building Science Corporation’s John Straube writes that ventilation cannot remove a lot of heat, so it usually works only once the sources of heat have been removed or reduced drastically. What makes it work:

  • Intake low, exhaust high. The Department of Energy calls a continuous ridge vent along the peak combined with continuous soffit vents at the eaves the most effective arrangement, and notes that few existing homes are built that way. The Solution Center warns against venting the exhaust side more than the intake side: when the high vents move more air than the soffits can supply, heated air can be drawn up from leaks in the ceiling to make up the difference.
  • Enough vent area. The residential code in all three states asks for a net free vent area of 1/150 of the vented space, or 1/300 when 40 to 50 percent of it sits within 3 feet of the ridge and the rest is in the bottom third of the attic. In climate zone 6, which takes in part of the Hudson Valley, the 1/300 option also needs a vapor retarder on the warm side of the ceiling.
  • Baffles in every rafter bay. Where there are soffit vents, the code says insulation must not block the free flow of air, and requires at least a 1-inch space between the insulation and the roof sheathing at the vent. With loose-fill or batt insulation in a vented attic, the energy code adds a baffle at the soffit and eave vents that extends over the top of the insulation. The Solution Center and the DOE guide both recommend a 2-inch channel, more than the code minimum, and Building Science Corporation says every rafter bay must be ventilated, not every third one. ENERGY STAR calls blocking the airflow at the eaves the most common mistake homeowners make when they insulate.

Cutting in soffit or ridge vents is roofing and carpentry work. Baffles, and keeping the insulation clear of the vents, are part of the insulation job.

4. Deal with heat sources in the attic

The DOE guide says leaky heating ducts in a vented attic can melt the snow on the roof and lead to ice dams, and the Solution Center says it is best to keep mechanical systems out of the attic and locate them in conditioned space. Sealing and insulating the ducts that stay in the attic helps; moving the equipment is work for an HVAC contractor. The other route is to bring the attic inside the insulation. The Solution Center lists closed cell spray foam on the underside of the roof deck, which air seals and insulates in one layer, as one way to build an unvented attic for ice dam prevention, and cautions that any departure from a simple vented attic takes more planning and is less forgiving of mistakes. An unvented attic has its own section of the residential code, R806.5, and our roof insulation guide covers how it is built.

What doesn’t fix ice dams, and what makes them worse

  • More insulation alone. The DOE guide says simply adding insulation will not solve winter problems such as ice dams and icicles, and may even create new ones. Building Science Corporation says airtightness is more important than insulation levels, though both are important.
  • More vents without sealing. Building Science Corporation says adding ventilation openings to a leaky attic is likely to increase the problem by giving the leaking air easier access to the outdoors, and that trying to ventilate away gross air leakage is very difficult and bad practice. Once most of the leaks are sealed, ventilation helps.
  • Powered attic fans. The DOE guide says Building America scientists do not recommend powered roof fans: they consume more energy than they save, increase the stack effect, and can cause backdrafting of fireplaces and unsealed gas- or oil-burning appliances. The University of Minnesota Extension says mechanical attic ventilation is not a recommended solution to ice dams in Minnesota and may cause undesirable negative pressure in the home.
  • Chipping, hacking or pounding the ice. Building Science Corporation’s photographs show the damage hacking at an ice dam does to a roof, and FEMA’s snow load safety guide says not to use sharp tools such as picks to remove roof snow.
  • Heat cables. They keep a channel open near the cable and leave the heat loss that made the dam. More on them below.
  • An ice barrier under the shingles. A good layer to have, and required in places, but it limits the damage rather than preventing the dam; more on it below.
  • Blaming the gutters. An archived University of Massachusetts Amherst building technology article puts it flatly: contrary to popular belief, gutters do not cause ice dams. It adds that gutters do concentrate ice and water at the vulnerable eave, where full gutters can bend and tear away. FEMA’s snow load guidance goes a step further: if the roof drainage system is blocked or poorly maintained, ice dams may form and concentrate the load at the eaves. Keep gutters clear, checked before winter. The melting itself still starts upslope, with heat from the house.

Heat cables: a stopgap, not a fix

Roof heating cables, the zigzag wires along the eaves, keep a path open so some meltwater can drain. They don’t touch the cause. North Dakota State University Extension calls the heat lost into the attic wasted heat, says that trying to remedy ice dams with electric cables on the roof deck also wastes energy, and says the key is to minimize the heat loss into the attic. A 1979 University of Minnesota extension fact sheet says the melting reaches only a few inches from the cable and that the sawtooth melt pattern often grows secondary ice dams farther up the roof. The archived UMass Amherst article says the cable creates an ice dam just above it, and that over time heat tape embrittles shingles and creates a fire risk. Building Science Corporation’s summary: with heat cables, we throw energy at the problem.

If cables are already on the roof, treat them as a stopgap for the season while the attic is fixed, not as the fix. Installing or servicing them is electrical work.

If you have an ice dam right now

Water coming through a ceiling in February is an emergency, and the urge is to get up a ladder with a hammer. The safer moves, from the extension services and agencies that write about it:

  • Stay off the roof. The University of Minnesota Extension says anyone on the roof during the winter, or performing work on the roof from below, risks injury and may damage the roof and house, and that it is important to contact professionals for the job. OSHA, writing for workers, says falls cause the most deaths and injuries during rooftop snow removal.
  • Rake only from the ground, and only where you can reach. A Cornell Cooperative Extension winter safety booklet says a long-handled roof rake lets you stay on the ground when clearing a single-story roof. Use a non-metallic one: FEMA says metal rakes can damage roofing and pose an electrocution risk. Stand back from the eave, outside the range of snow that can slide at any moment, watch for dislodged icicles, and leave at least 2 inches of snow on the roof so the roofing isn’t damaged. Raking cuts the snow that feeds the dam; it doesn’t make one impossible. The University of Minnesota Extension notes that even a roof rake may damage the roofing, and OSHA’s guidance for workers is to keep snow rakes at least 10 feet from power lines and never to use a rake or shovel while on a ladder.
  • A drain path is an emergency measure, done from the ground. For water flowing into the house, the University of Minnesota Extension describes making channels through the dam so the water behind it can drain, by hosing with tap water on a warm day and working upward from the lower edge, and says the channel will become ineffective within days and is only a temporary solution. Never do it from a ladder; if the eave is out of reach from the ground, it is a job for the professionals.
  • Leave removal to the people who do it. Taking ice and snow off a roof is work for a roofer or an ice dam removal service. FEMA recommends a licensed, insured professional roofing contractor with experience removing snow from roofs.
  • Dry out the inside. The University of Minnesota Extension says to dry out wet or damp parts of the house immediately, and not to repair ceilings and walls until they are dry, doing the repair together with correcting the heat loss that created the ice dam, or the damage will occur again.

Signs of ice dam damage inside the house

Ice dams show themselves outside first: a ridge of ice along the eave, heavy icicles, and bare patches in the roof snow. The Department of Energy calls icicles a telltale sign that ice dams are forming. Inside, the signs are water and what it leaves behind:

  • Water stains on ceilings and the tops of outside walls. The University of Minnesota Extension says the water can flow from the attic into exterior walls or through the ceiling insulation and stain the ceiling finish.
  • Peeling or blistered paint, inside or out. The UMass Amherst article notes that paint often peels long after the ice and all signs of a roof leak are gone, which makes the cause easy to miss.
  • Wet, matted or compressed insulation at the eaves. Wet insulation doesn’t work well, and the same article says water-soaked insulation stays compressed even after it dries, so it insulates less than it did.
  • Damp roof sheathing, trim or insulation, worth checking whenever ice dams form, from the attic and outside, as the UMass article advises.

One more sign points at the same air leaks rather than at ice dam water: frost or water drops on the nail tips poking through the roof sheathing in cold weather. A Cornell fact sheet says water and frost are often most visible there, and that lots of icicles at the roof edge make attic condensation problems probable too. Both come from the same escaping house air: its moisture causes the condensation and its heat the ice dams.

ENERGY STAR’s do-it-yourself guide treats a history of ice dams in the winter as an indication of serious air leaks, and lists it, along with wet or damp insulation, among the problems you may need a contractor to correct. The DOE guide says both must be corrected before insulation is added.

Why Cape Cods, knee walls and cathedral ceilings get ice dams

The Department of Energy’s Building America program calls the story-and-a-half Cape Cod especially vulnerable to ice dams and frost on the underside of the roof deck, and lists why: finished interior walls, shallow rafter depths, no raised-heel trusses, thermal bridging and gaps in the air barrier, all of which prevent thorough insulation, air sealing and ventilation from the inside. The same weak spots turn up in finished attics and bonus rooms built on the same plan.

Knee walls and the floor behind them

A knee wall is the short wall of a finished attic room, with an unheated wedge of attic behind it. The DOE’s knee wall brief says knee walls are often left uninsulated and that the open cavities between the floor joists beneath them are often a big source of air leakage. The Solution Center adds that heat lost into the attic can warm the underside of the roof deck and contribute to snow melt and ice dams. Its fix is blocking in the joist bays below the knee walls to stop air flowing under them, then an air barrier and insulation on the knee wall itself. The New Jersey and New York energy codes require an air barrier between the conditioned and unconditioned sides of an attic knee wall, and all three states require knee walls to be sealed. The other approach the DOE describes is to carry the insulation down the roof line to the attic floor and air seal it there, which brings the side attic inside.

The sloped ceiling of a half story

Between the knee wall and the flat upper ceiling, the rooms of a half story usually have a sloped section with the ceiling fastened to the rafters. Building America researchers say a continuous air barrier, continuous insulation and effective roof ventilation are all difficult to achieve from the inside once the attic is finished living space, the rafters are shallow and the roof is cut up with dormers, and that venting the roof deck from the inside is extremely difficult if not impossible. They describe exterior insulation added over the roof deck, a reroofing job, as a long-term solution. From the inside, what can be done depends on whether the finished ceiling is coming off; with the bays open, closed cell foam puts the most R-value in a shallow bay.

Cathedral ceilings and skylights

A cathedral ceiling has no attic to buffer it. Any air leaking through the ceiling or around a recessed light reaches the roof deck directly, and the insulation can only be as deep as the rafters. The residential code requires enclosed rafter spaces to be ventilated, with the same 1-inch space at the vent, unless the roof is built as an unvented assembly under its separate rules. Skylights add a warm spot: the UMass Amherst article notes ice dams also form below skylights because they are low-R assemblies, and the University of Minnesota Extension lists recessed lights, skylights, complex roof designs and heating ducts in the attic as things that increase the risk. Dormers, valleys and other breaks in the roof are harder to air seal, insulate and ventilate, the Solution Center says, which is why those are the spots that need the most care.

The ice barrier the roofing code requires in NJ, NY and CT

The residential code’s roofing chapter deals with ice dams from the outside, with an ice barrier at the eaves when a roof is put on or replaced. Apart from where it applies, Section R905.1.2 reads the same in substance in all three states: for asphalt shingles, metal roof shingles, mineral-surfaced roll roofing, slate and slate-type shingles, and wood shingles and shakes, the ice barrier is at least two layers of underlayment cemented together, or a self-adhering polymer-modified bitumen sheet used in place of normal underlayment, running from the lowest edges of all roof surfaces to a point at least 24 inches inside the exterior wall line of the building. On roofs of 8 in 12 or steeper it must reach at least 36 inches along the slope from the eave. Detached accessory structures with no conditioned floor area are exempt. Where it is required depends on the state:

  • Connecticut (2021 IRC portion of the 2022 Connecticut State Building Code): the state’s climatic and geographic design table answers “YES” for ice barrier underlayment, statewide.
  • New Jersey (2024 One- and Two-Family Dwelling Subcode): New Jersey rewrote the trigger to areas where the average daily temperature in January is 25°F or less, and the Department of Community Affairs’ Bulletin 07-3 says that area is Sussex County. Elsewhere in the state the code doesn’t require one, which is a minimum, not advice against one.
  • New York (2025 Residential Code of New York State): the code requires an ice barrier where there has been a history of ice forming along the eaves, and leaves it to the local authority having jurisdiction to enter “YES” or “NO” in the design table based on the local history of ice dam damage. Your town or village building department can tell you its answer.

An ice barrier is roofing work and a good layer to have, but it is protection, not prevention. Building Science Corporation says it does not prevent the ice dam from occurring; it only limits the damage. Stopping most ice dams happens in the attic, and the membrane covers the ones that still form.

Where ice dams form in NJ, NY and CT: climate zones and programs

Connecticut sits entirely in climate zone 5. New Jersey’s 2024 energy code puts Bergen, Hunterdon, Morris, Passaic, Somerset, Sussex and Warren counties in zone 5 and the rest of the state in zone 4. In New York, Westchester, Nassau and Suffolk are zone 4; Rockland, Putnam, Dutchess and Orange are zone 5; Ulster and Sullivan are zone 6. The Solution Center says the sustained freezing temperatures and lasting roof snow behind ice dams are most prevalent in climate zones 5 and colder, and notes that the model building codes don’t specify regions where ice dams occur and reference historical precedent instead, which is how New York’s code still handles the ice barrier. By that measure, zone 4 houses on Long Island, in Westchester and across most of New Jersey see them less often, but in a snowy winter the same three conditions can line up anywhere: snow on the roof, a leaky or thinly insulated attic, and a stretch of freezing weather.

State and utility programs offer incentives toward some of this work, mainly air sealing and attic insulation, when their own assessment recommends it. NYSERDA says the contractors who offer its Comfort Home “seal and insulate” packages can help solve common problems including roof ice dams in winter; its program manual says homes served by PSEG Long Island are not eligible, and PSEG Long Island runs its own home energy assessment. New Jersey’s utilities run Whole Home Energy Solutions through BPI-certified participating contractors. Energize CT’s 2026 insulation rebate covers attic floors where the existing insulation is R-19 or less, along with floored-over attics, walls, basement and garage ceilings and rim joists; a roof deck is not on its list, the insulation must be recommended during a Home Energy Solutions visit, and the professional-installation rebate requires a contractor from its Insulation Installers Network. More on the programs in each state is on our New York and New Jersey rebates and Connecticut rebates pages. The federal homeowner tax credit for insulation, Section 25C, ended for anything placed in service after December 31, 2025. Our insulation tax credit guide covers what ended and what 2025 work can still claim.

Common questions about ice dams

What is an ice dam?

A ridge of ice along the edge of a roof that stops melting snow from draining off. Heat from the house warms the upper roof deck above freezing while the eaves stay below it, so snow melts high on the roof and refreezes at the cold edge. The University of Minnesota Extension says the heat primarily comes from the house and only rarely from the sun.

Does air sealing stop ice dams?

It is the most important step, the Department of Energy’s Building America Solution Center says, but not the only one. Seal the attic floor (top plates, chases, flues, hatches and recessed lights), then insulate to at least code depth with full depth carried over the outside walls, and vent the roof deck from soffit to ridge with a baffle in every rafter bay.

Will more attic insulation stop ice dams?

Not on its own. Fiberglass and cellulose slow conducted heat but let air through, and the Department of Energy says simply adding insulation will not solve problems such as ice dams and may create new ones. Seal the attic floor first, then insulate to at least code depth, R-49 in New Jersey and New York or R-60 in Connecticut. ENERGY STAR recommends R-60 for an uninsulated existing attic.

Do I need more attic vents to stop ice dams?

Usually not as the first step. Building Science Corporation says adding vents to a leaky attic is likely to increase the problem by giving the leaking air an easier way out. Seal the leaks, then make sure the soffit vents are open behind baffles and the intake and exhaust are balanced. The Department of Energy and the University of Minnesota Extension both advise against powered attic fans.

Do heat cables work for ice dams?

They keep a channel open near the cable, but they treat the symptom. North Dakota State University Extension says using them wastes energy, and a 1979 University of Minnesota extension fact sheet says they melt only a few inches around the cable and can leave a new dam farther up the roof. At most they are a stopgap while the attic is fixed.

How do you get rid of an ice dam safely?

Not by chipping it. Hacking at the ice damages the roof, and the University of Minnesota Extension says anyone on a roof in winter risks injury and should contact professionals. If you clear snow, use a non-metallic roof rake only from the ground, stay clear of sliding snow, falling icicles and power lines, and leave at least 2 inches of snow on the roof, as FEMA advises. Taking the ice off is work for a roofer or an ice dam removal service.

Do gutters cause ice dams?

Not on their own. The heat that melts the snow comes from the house, and an archived University of Massachusetts Amherst article says gutters do not cause ice dams, though they concentrate ice and water at the eaves. FEMA adds that a blocked roof drainage system can let ice dams form. Keep gutters clear, checked before winter, and fix the attic.

Does an ice and water barrier stop ice dams?

No. A self-adhering ice barrier under the shingles limits the damage when water backs up, and when a roof is put on or replaced the code requires one across Connecticut, in Sussex County in New Jersey, and wherever a New York building department calls for it. Building Science Corporation says it does not prevent the ice dam from occurring. Keeping house heat off the roof deck prevents most of them.

Why does my Cape Cod get ice dams?

The Department of Energy calls the story-and-a-half Cape especially vulnerable: finished walls, shallow rafters, no raised-heel trusses and gaps in the air barrier make it hard to insulate, seal and ventilate from inside. The usual leaks are the open floor joists under the knee walls, the sloped ceiling bays and the top plates at the eaves, and blocking and sealing those comes first.

Are icicles a sign of ice dams?

Large icicles along the eaves often are. The Department of Energy calls icicles a telltale sign that ice dams are forming, and the Building America Solution Center says they are often a sign that more water is building up behind the dam. Small icicles from sun-melted snow usually don’t back water up, Building Science Corporation’s Joseph Lstiburek says.

Ice dam prevention in New Jersey, Connecticut, the Hudson Valley and Long Island

We work on the part that stops the next ice dam: the attic. That means pulling back old insulation where it is in the way, air sealing the top plates, chases, flues and hatches, blocking the joist bays under knee walls, foaming tight eaves, setting baffles in the rafter bays and bringing the attic floor to code depth or beyond, or spraying the roof deck where an unvented attic is the better plan. Roofing, ice barrier membranes, heat cables, ice removal and electrical work are separate trades, hired by you directly. The energy audit is free. It is our own, not a utility or state program’s assessment, so if you are counting on a rebate, book the program’s visit first.

Call 914-554-2289 or use the contact form, 8am–8pm, seven days. The Home Insulators is family-owned, based in New Rochelle, NY since 2015, with a 100-plus-person in-house crew that never subcontracts. We work across all of New Jersey, all of Connecticut, New York’s Hudson Valley and Long Island; see our service area.

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