Attic Insulation Calculator
What you have, what you need, and the inches between the two. Built on the Energy Star recommendations for the North Carolina climate zones.
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Over 1,400 sq ft. Bag coverage varies by brand, so buy to the chart printed on the bag.
Get the attic checked, freeWhere the numbers come from
Energy Star puts most of North Carolina in climate zone 3, where an uninsulated attic wants R49 and an attic with a few inches already up there wants at least R38. The mountains sit in zone 4, where the figure is R60.
Common attic insulation runs about R2.5 to R3.5 an inch, so reaching R49 from bare joists means somewhere between 14 and 20 inches depending on what you use. If you can see the tops of the joists, you are nowhere near it.
Air sealing comes first
Insulation slows heat moving through the ceiling. It does nothing about air moving through gaps, and an attic at R60 over unsealed light fittings, pipe penetrations and a drafty hatch still loses heat. Sealing those is cheap and it is the step most jobs skip.
The part that affects your roof
Insulation pushed into the soffit vents stops the attic breathing, and a hot damp attic shortens the roof above it. Baffles at the eaves keep the airway open, and our ventilation calculator works out the net free area the space needs. Topping up insulation without checking ventilation trades a lower power bill for a shorter roof.
Common questions
How much attic insulation do I need in North Carolina?
R49 for most of the state, which is Energy Star's recommendation for climate zone 3. R38 is the lower figure where there is already insulation in place. Western North Carolina sits in zone 4 and the recommendation there is R60.
How many inches is R49?
Between 14 and 20 inches depending on the material. Blown cellulose runs about R3.5 an inch, fiberglass batts about R3.2, and blown fiberglass about R2.5.
Can I put new insulation over old?
Usually yes, and topping up is the normal way to bring an attic to current levels. Do not use faced batts over existing insulation, because the vapor retarder ends up buried in the middle of the assembly where it traps moisture.
Does more attic insulation damage my roof?
Not on its own. Insulation blocking the soffit vents does, because the attic stops breathing and the deck runs hot. Baffles at the eaves cost very little and prevent it.
Will new insulation lower my power bill?
In an attic that is well short of R38, usually yes, and cooling is where most of it shows up here. The saving depends on the house, so we will not put a figure on it without looking.
Should I air seal before insulating?
Yes, and it is the cheaper half of the job. Gaps around recessed lights, plumbing stacks, the chimney chase and the attic hatch leak air straight past any amount of insulation.
Get your attic looked at, free
We get on the roof, photograph what is actually there, and hand you a written report with a price. No charge, and no obligation to book the work with us. If the roof has years left in it, that is what the report will say.
Give us a call or fill out our form today to schedule your free inspection!
Whether you need a roof replacement, roof repair, or annual inspection, we’ve got you covered.