Already have some insulation in the attic? Enter what you have and the R-value you want. You get the R-value to add, the extra depth and the volume of material.
Your shopping list
10.27 inDepth to add
38 RR-value to add
1,129.73 cu ftVolume of insulation
- Area with extra1,320 sq ft
This adds on top of what you have. Keep air flowing at the eaves. Extra of 10% is included.
How to use the Attic Insulation Calculator
- Measure the attic floor area.
- Push a ruler into the insulation to find its depth. Multiply by the R-value per inch, or read it from old paperwork.
- Pick a target R-value and a material, then read the depth to add.
The math behind it
R to add = target R – existing R
Depth to add = R to add / R-value per inch
Volume = area x depth / 12
A worked example
What we typed in
- Attic floor area: 1,500 sq ft
- R-value you already have: 19
- Target R-value: R-49
- Insulation material: Blown cellulose (about R-3.7 per in)
- Extra for mistakes and cuts: 10%
What we got
- Depth to add: 8.11 in
- R-value to add: 30 R
- Volume of insulation: 1,114.86 cu ft
- Area with extra: 1,650 sq ft
Tips from the job site
- Keep insulation back from the roof edge so air can still flow in through the soffit vents.
- Air seal around lights, pipes and the attic hatch before you add insulation.
Common questions
How do I find the R-value I already have?
Measure the depth in inches and multiply by the R-value per inch of that material. Old and flattened insulation gives a bit less than the label says.
Should I take out the old insulation?
Not if it is dry and clean. Add new insulation on top until you reach your target.
See all Insulation Calculators.
Last checked: (worked example and form display).