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Attic insulation calculator: bags and RSI
Estimate the number of Johns Manville Climate Pro bags for an attic layer from a target RSI and the manufacturer’s product chart.
Your result
Your plan starts
with a few details.
Enter the attic area and target RSI to estimate product bags for that attic layer.
How it works
Enter your attic floor area in square metres and the target RSI for your project. The calculator chooses the next supported RSI row from the Johns Manville Climate Pro attic chart. Use the NRCan national recommendations below as location-based guidance when choosing a target.
The bag estimate scales the manufacturer’s published minimum bags per 100 m² to your attic area and rounds up to whole bags. The selected thickness, RSI and R-value are product-chart figures. This is a product-source layer estimate, not a determination of national or provincial code compliance.
NRCan targets vary by heating degree-day zone. Confirm the right zone for your location and check the current bag label and installation instructions. The product chart does not assess whether a particular attic assembly is suitable for added insulation.
Formula
Set the target
Target RSI = the project value you enterNRCan national recommendations by heating degree-day zone are shown as guidance.
Choose a charted product layer
Selected layer = next supported product RSI at or above the targetThe manufacturer chart has discrete product thickness and RSI rows.
Count whole bags
Bags to buy = ceil(attic area ÷ 100 m² × published bags per 100 m²)This uses the manufacturer’s bag-rate column rather than inverting rounded coverage values.
Worked example
Set the project target
Target RSI = 9.7This example target also matches the NRCan recommendation for HDD zone 5.
Choose the supported product row
Next Climate Pro row = RSI 9.8 (R-56) at 472 mmThe product chart has no RSI 9.7 row, so the next higher row is used.
Scale the published bag rate
100 m² ÷ 100 × 29.1 bags = 30 bagsThe 9.8 RSI chart row lists 29.1 minimum bags per 100 m², the fractional amount is rounded up.
Assumptions and safety
This estimate covers a single product layer based on the entered target RSI. It does not subtract existing insulation or account for attic shape, eaves, obstructions, air leakage, ventilation, moisture, settling, installation equipment or waste. A suitable retrofit may need an assessment of the full roof and ceiling assembly.
Maintain required clearances from heat-emitting devices and recessed lights, and keep attic ventilation clear. Control air leakage and moisture before adding insulation. Follow current product instructions and local safety requirements, consult a qualified professional if you are unsure about wiring, combustion appliances or the existing assembly.
Frequently asked questions
Does this result prove that my attic meets Canadian code?
No. NRCan recommendations are used as context and the quantity comes from one product chart. This estimate is not a national or provincial code-compliance result.
How do I choose a target RSI?
Use the NRCan recommendations as location-based guidance and confirm the heating degree-day zone for your location. The calculator lets you enter the target RSI directly, it does not infer a zone from a postal code.
Why can the selected RSI be higher than the zone recommendation?
The Climate Pro chart lists discrete product layers. The calculator selects the next available RSI that is at least as high as the selected national recommendation.
Are safety clearances included in the bag estimate?
No. The estimate is area-based. Follow the cited product and NRCan safety guidance, including clearances and ventilation requirements.
Sources
Specs as of: