Why does attic ventilation matter in winter?
Because a cold attic keeps the roof the same temperature from the ridge to the eaves. ENERGY STAR explains that letting outdoor air flow naturally through the attic in winter helps keep it cold, which reduces ice damming: snow that melts off a roof over an attic that is too warm and freezes again at the gutters.
The University of Minnesota Extension describes the same thing from the roof's side: an ice dam needs the upper roof above 32 degrees F and the eaves below it. In summer the same airflow moves hot air out of the attic, which ENERGY STAR says protects the shingles and removes moisture.
Is air sealing more important than ventilation?
Yes, and it comes first. The Department of Energy's Building America Solution Center calls sealing the air leaks from the house into the attic the most important step, and the University of Minnesota Extension names air leakage as a major way homes lose heat into the attic.
ENERGY STAR's advice is to plug the big holes first. The usual places are where walls meet the attic floor, dropped soffits, the spaces behind and under knee walls, and the opening around a furnace flue or chimney. Ventilation cannot carry away heat that pours into the attic faster than the vents move air.
How much insulation does an attic need?
Enough that the heat stays in the house. The Department of Energy says adequate attic insulation keeps heat from reaching the roof deck, and its guide to building against ice dams recommends R-60 or more in a vented attic in climate zones 5 and colder. Your energy auditor or the code official can tell you which zone your house is in.
Order matters here too: ENERGY STAR recommends sealing the attic before adding insulation, because insulation over open air leaks lets warm, moist air keep moving through it.
What does the code require for attic ventilation in Omaha?
Omaha adopted the 2018 International Residential Code, whose roof ventilation section (R806) sets the minimum vent area and the airspace that has to stay open between the insulation and the roof deck at the vents. The Department of Energy recommends keeping a 2 inch vent space there, which it says works better against ice dams than the 1 inch minimum in the IRC through the 2021 edition.
ENERGY STAR's rule for the eaves: never cover soffit vents with insulation. Rafter vents (insulation baffles) stapled to the roof deck between the rafters keep a channel open, so outside air moves in at the soffits and out at the ridge or gables. Omaha's code also requires an ice barrier underlayment on a new roof, the second line of defense when a dam does form.
Will an attic fan stop ice dams?
No. The University of Minnesota Extension says mechanical attic ventilation is not recommended as a fix, because it can create other attic moisture problems and may pull the house into undesirable negative pressure. ENERGY STAR adds that an attic fan over an attic that is not sealed from the house sucks conditioned air up into the attic.
Natural ventilation, soffit to ridge, over a sealed and insulated ceiling is the combination all three sources describe.
What else warms the roof?
The University of Minnesota Extension lists exhaust systems that end just above the roof, chimneys, leaky or poorly insulated ductwork in the attic, and knee wall spaces. Each puts heat under part of the roof.
If one has already formed, Rocket Roofing General Contractor steams ice dams off the eaves; if it leaked, start with what to do when an ice dam leaks. Our post on preventing ice dams on Nebraska roofs covers the season's other steps.
Which attic leaks should be sealed first?
The big ones. ENERGY STAR's attic air sealing project says to plug the big holes first, because that is where the biggest savings are, and points to the usual places: the attic floor where walls meet it, dropped soffits, and the spaces behind and under knee walls. It also names the opening around a furnace flue or chimney as a potential major source of warm air into the attic.
How are rafter vents installed?
Between the rafters, where the attic floor meets the roof. ENERGY STAR says rafter vents, also called insulation baffles, are stapled directly to the roof decking, come in 4 foot lengths and in 14 1/2 and 22 1/2 inch widths for different rafter spacings, and are what let the attic floor be insulated all the way out to the eaves while the soffit vents stay open. Without them, insulation pushed to the edge blocks the very air that keeps the eaves cold.
Should ducts and equipment be in the attic?
The Department of Energy's guide to building against ice dams says to keep heating and cooling equipment out of the attic, and to make the insulation over the exterior wall top plates at least match the wall's own insulation. The University of Minnesota Extension lists leaky or poorly insulated ductwork in the attic among the heat sources behind ice dams.
How old are the attics in Omaha?
Many are as old as their houses. The Census Bureau's American Community Survey (2019 to 2023 five-year estimates) puts the median year Omaha's housing was built at 1972, with about 18 percent built before 1940 and about 62 percent before 1980. An attic is as sealed and insulated as the last work done on it, which is why the order above, sealing first and insulation second, is the place to start on an older house.
Who is Rocket Roofing General Contractor?
Rocket Roofing General Contractor has served Omaha, Papillion and the rest of Nebraska since 2008. We are registered with the Nebraska Department of Labor, NE DOL #98741-26, and we are a GAF Certified Residential Roofing Contractor. Our crews physically clear snow and ice from roofs and steam ice dams. Headquarters: 5634 S 85th Cir Ste 204, Omaha, NE 68127. Call us at (402) 291-8888.