Can you over insulate a house?

Online Answer
It is possible to over-insulate your house so much that it can't breathe. The whole point of home insulation is to tightly seal your home's interior. But if it becomes too tightly sealed with too many layers of insulation, moisture can get trapped inside those layers. That's when mold starts to grow.
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According to ENERGY STARĀ®, you can put new insulation over old insulation, "unless it is wet. ... "Faced" insulation should not be placed on top of existing insulation in the attic. Any new roll or batt insulation installed over existing insulation in the attic needs to be without a vapor retarder (face).
Non-Toxic Mineral Wool Brands Rockwool (formerly Roxul) is the most common and accessible mineral wool insulation. They have a newer version called AFB, that does not contain formaldehyde. The binder is an undisclosed polymer (a plastic, likely acrylic), it also contains mineral oil.
Use natural materials, if possible, in areas of the house with low or no moisture. Options include cotton from post-industrial scrap denim, sheep's wool, hemp and cellulose from recycled newspaper, and other natural fibers. Keep in mind that cellulose insulation runs the risk of settling over time..
Closed cell foam has the highest R-value of any insulation, around R-6.2 per inch, but can be expensive.
The most common way of insulating behind your radiator is to remove it from the wall, and to install a foil based lining, often expanded polystyrene based behind the radiator, on the wall. ... Obviously you need to turn the radiator off before you work behind it, or remove it from the wall for your own safety.