Cellulose Attic Insulation Over Fiberglass

You can get to the same place with either material.

Cellulose attic insulation over fiberglass.

This can be added on top of old. The bottom line is that cellulose can burn but fiberglass will not support combustion. Do not tack down roll or batt insulation because compacting reduces its effectiveness or r value. Loose fill cellulose is relatively inexpensive yet still has an r value of about 3 5 per inch of thickness compared to fiberglass r value between r3 to r4 per inch.

If fiberglass batts become compressed losing some of their air pockets then this insulation may be more affected by air flow than cellulose which performs well regardless of density. When there are fiberglass batts in your attic the cellulose will not draft block the top plates. It will however fill in all the gaps that fiberglass batts leave along side of your ceiling joists if you see wood its no good and add the to your r factor cellulose is second best with spray 2 part high density spray foam as first in my book. This problem has been successfully solved by installing fiberglass batt insulation over the top of loose fill or blown insulation.

When walls are already finished injecting loose fill cellulose insulation is one of the few ways of adding. Unless you opt for spray foam then the insulation choices normally come down to cellulose and fibreglass. Also cellulose is a dusty product whereas fiberglass blows in pretty clean. This type of insulation material will not shrink over time.

Click the button to calculate the depth in inches and pounds of total insulation required for this job. Assuming your current attic insulation is made from fiberglass and has a value of r 13 you d have to add roughly 10 inches of additional fiberglass to hit r 38. This type of insulation typically fiberglass or cellulose insulation can be added over existing insulation provided it s installed perpendicular to joists. The trapped air molecules in the insulation are pulled up through the insulation into the colder attic air.

To install fiberglass batts over existing insulation lay the batts perpendicular to the joists so they do not compress the insulation below. Input length width and desired r value of the area to be insulated. I ve been insulating for over 30 years and we have never added cellulose over fiberglass. Loose fill cellulose insulation can settle around and conform to most of the obstructions found in walls and attics.

This calculator is to be used as an estimating tool only. Insulation works better when you add the same type to existing material. Just piling material up in an attic doesn t always make for a better insulated space. Roll or batt insulation.

The two main least expensive and most commonly used residential insulation materials is cellulose and fibreglass.