Installing a new insulation material allows you to get a higher R-value of heat-loss prevention without making your walls and ceiling cavities any larger. However, don't forget to factor in the cost of removing the existing insulation and installing new spray foam or the cost of rigid foam boards, blown-in loose fill, or other advanced materials. It's often essential to clear out the old stuff first for at least one of these five reasons.
First, definitely have your insulation removed if it has any signs of pest infestation in the present or past. Common signs include:
- Tunnels and nests made out of fluffy batt or loose fill materials
- Urine and feces from animals
- Insect droppings and shed exoskeletons
- Signs of digging or depressions in the insulation that compact the material.
Insulation that was or is home to animals and insects is full of diseases, bacteria, and dust that can lead to serious lung irritation and damage. It's essential to remove all of the affected material, even if you weren't planning on replacing it before discovering the problem, to prevent the problem from spreading further. Just eliminating the pests won't stop the bacteria they carried in from growing and spreading.
Check for signs of moisture in the insulation when evaluating it from removal as well. It's usually fine to install successive layers of material in a completely dry attic or wall space, but even the smallest amount of moisture can become a major source of mold and structural rot when it's trapped under another few inches of fiberglass or foam. Remove any material that has gotten wet, even if it's dry now, and seal the source of the moisture before adding anything new to the part of the home that is affected by the leak.
It's also worth the extra work to remove existing insulation when it was improperly installed in the first place and is causing damage to the structure. For example, spray-foam insulation isn't supposed to be attached directly to the backside of siding without a moisture barrier because it creates a channel for water to run into the rest of the structure. If you or a home inspector has discovered this kind of contact issue in the home prior to a renovation, now is the perfect time for fixing the problem—before you're paying for more extensive repairs due to years of rot and water damage.
Don't forget that some common home-insulation materials are dangerous on their own and should be removed as soon as possible to protect your family's health. Panels made from asbestos were rarely used in some homes dating back to the turn of the century, but vermiculite is a common form of expanded minerals that was used into the 1990s. This puffy popcorn-like material is a source of asbestos dust that can shake down into the rest of the home and lead to a deadly lung condition. It's essential to only let professional insulation experts handle the removal process for your safety.
Finally, some insulation materials just don't work well together. For example, you can't press down fluffy fiberglass batts to squeeze rigid foam boards into a tight ceiling space, or else you'll lose all of the insulation value of the existing layer. It's also a bad idea to stack layers of paper-covered or faced insulation in your attic or crawlspace because the covers create air gaps that interfere with insulation value. Spray foam only works properly when applied directly to a moisture barrier or over rigid boards, so you'll need to remove any loose or batt material first in order to upgrade to this form of insulation when you do your home renovations.