Can you put new insulation on top of old insulation?

Author: Pauline Schmidt IV  |  Last update: Sunday, February 1, 2026

In many cases you can add new insulation on top of old insulation, unless the old insulation is wet, mouldy, or vermiculite. If the old insulation is dry but appears to have previously been wet, you should look for the cause and repair the problem.

Should I remove old insulation before adding new?

Removing old insulation is generally recommended if it's damaged, contaminated with mold, or infested with pests. However, if the insulation is in decent shape and just needs a boost, adding a new layer on top can be a cost-effective option.

Is it OK to double up insulation?

As a general guideline, it's advisable to install double layers of thermal insulation throughout your house. Nevertheless, this may not be feasible in all areas due to space limitations. Typically, it's not practical to add two layers of insulation within the walls of your home.

Can you put insulation on top of existing insulation?

In many cases you can install new insulation over old. Your old insulation may not be very effective on its own any more, but it probably has some insulating power.

Do insulation installers remove old insulation?

Any reputable insulation installer will thoroughly remove old insulation before putting in the new. However, as a homeowner, you should double-check that they remove all of the old insulation as a first step.

Can I Put New Insulation over Old Insulation in my Home?

Is it OK to layer insulation?

In many cases you can add new insulation on top of old insulation, unless the old insulation is wet, mouldy, or vermiculite. If the old insulation is dry but appears to have previously been wet, you should look for the cause and repair the problem.

Can you put too much insulation?

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.

Where should you not put insulation?

Never place insulation close to water heaters, oil burners or anything hot. The backing is especially flammable and will be a major fire hazard for your home.

Is there a big difference between R13 and R19 insulation?

R19 Insulation offers superior thermal insulation compared to R13. With a typical thickness of 6.25 inches, R19 fiberglass is designed for use in 2x6 wall cavities, making them suitable for colder climates where higher thermal resistance is necessary.

Is 2 inches of insulation enough?

The recommended thickness for attics is typically 12-16 inches. Spray foam insulation: As discussed earlier, the recommended spray foam insulation thickness can vary depending on factors like climate and location. For attics, a thickness of 2-4 inches is usually sufficient.

Should I replace 20 year old insulation?

However, insulation can start falling from fiberglass batts after 15 to 20 years, so if your insulation was installed in batts well over a decade ago, it might be time for an inspection or a home energy audit.

How much does it cost to replace insulation?

The average U.S. homeowner spends about $1,852 to install insulation. Depending on the type of insulation, square footage, site location, and material, you might spend anywhere from $498 to $4,500. Insulation can keep your home cozy and warm on long winter nights or cool and comfortable on hot sunny days.

How much value does new insulation add?

The Types of Insulation That Have the Highest Resale Value

However, according to a study by the National Association of Realtors, insulating attics and walls with cellulose or fiberglass can have the highest return on investment at 107% and 95%, respectively.

Can your R-value be too high?

The optimal R-value for most homes is 30, but you can go as high as 38 if you live in a tropical climate. Anything higher than 38 indicates an over-insulated space. While you might think that too much insulation can't be bad, there are some significant consequences to consider.

Is it okay to cover attic insulation with plywood?

Can I put plywood over insulation in the attic? Yes you can install plywood subflooring directly over the floor joists and insulation on your floor. You need to install rigid insulation boards on top of the attic flooring joists and then install plywood over the top.

Is it OK to squish insulation?

What Happens If You Compress Blown-In Insulation? Like batts, compressing blown-in fiberglass insulation improves the R-value per square inch while diminishing the overall R-value. Also like fiberglass batts, some amount of compression is OK if the cavity is completely filled.

Can I put new insulation on top of old insulation?

The answer is yes, you can put new insulation over old. But there are some circumstances that would require insulation removal first, such as in the case of contaminated insulation from pests, water or smoke. Moisture is the biggest culprit, as it can lead to mold and mildew, as well as ceiling and roof rafter rot.

What happens if you double insulation?

If your building is located in an area with extreme weather conditions, double insulation can be a game-changer. For instance, in regions with harsh winters, double insulation can prevent heat loss, keeping the interior warm and comfortable.

Should you leave a gap between insulation and roof?

It's important to leave a ventilated air gap between the insulation and the boards to prevent condensation on the underside of the boards.

Which is better, attic insulation blown or rolled?

Blown fiberglass insulation scores an R-value of 3.2 to 3.8, making it slightly less likely than rolled fiberglass to prevent the flow of heat into and out of your house. That being said, though, blown fiberglass insulation isn't meant to cover huge areas like rolled fiberglass insulation.

How many inches of insulation should be in my attic?

The higher the R-Value, the better the thermal performance of the insulation. The recommended level for most attics is to insulate to R-38 or about 10 to 14 inches, depending on insulation type.

How often should attic insulation be replaced?

However, due to its construction with natural materials, eventually the product will lose effectiveness. Fiberglass insulation typically needs to be replaced 15-20 years into it's life, as it can easily become dirty, wet, moldy, and ineffective if there's a roof leak or water damage of any kind.

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