Can you put in too much insulation?

Author: Miss Georgiana Howell  |  Last update: Friday, July 4, 2025

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.

What happens if you use too much insulation?

In fact, adding too much insulation to your walls can lead to problems such as poor ventilation, mould growth, and condensation. This is because thicker insulation can block airflow and trap moisture, leading to indoor air quality issues and even structural damage.

Is it okay 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.

Is it possible to over insulate an attic?

Yes, it is possible to put too much insulation in a loft or attic.

Can too much insulation cause mold in walls?

Many of us know what causes mould; when moisture is trapped in the rooms of you home. Sometimes, there is insufficient insulation in the walls, so mould grows. However, not many people realise that additional insulation isn't always the answer. In fact, too much insulation can be the secret cause of mould.

Is Too Much Insulation in the Attic Bad? | Foam University

Can a house be too well insulated?

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.

How long does it take for mold to grow on insulation?

The PROBLeM wiTh MOLd

Mildew (mold in early stage) and molds grow on wood products, ceiling tiles, cardboard, wallpaper, carpets, drywall, fabric, plants, foods, insulation, decaying leaves and other organic materials. Mold growths, or colonies, can start to grow on a damp surface within 24 to 48 hours.

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.

Can you have too high of an R-value insulation?

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.

Does extra insulation really help?

Unless your home was specially constructed for energy efficiency, you can probably reduce your energy bills by adding more insulation. Many older homes have less insulation than homes built today, but even adding insulation to a newer home can pay for itself within a few years.

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.

Can you put 2 layers of insulation in attic?

You should install two layers of insulation in your attic; wood joists must be covered to allow the air to move. The first layer will sit between the joists, and the second layer will run perpendicular over the joists. The first layer should have the facing against the drywall to act as a vapor barrier.

Can you put insulation in wrong?

Every type of bulk insulation in common use will block heat equally well whichever way it is installed. EXCEPT… some insulation includes a moisture barrier, and that must be installed right-way round to prevent moisture problems. But the insulation itself works both ways.

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.

How much insulation can I put in my attic?

If you live in the Southern part of the U.S., the recommended insulation level is a minimum of R-38 or about 13-14 inches of insulation. If you live in the Northern part of the U.S., the recommended insulation level is a minimum of R-49 or about 16-18 inches of insulation.

Can I double up R13 insulation?

Adding two R-13, 3.5” batts to a 2”x6” (5.5”) wood stud cavity will not provide an R-26. The total of 7” of insulation is reduced in thickness to 5.5” thereby losing the R-value associated with its full thickness.

How do you know if you have too much insulation?

Your walls or floors are always cold. Your home is drafty, especially in certain areas. You notice water leaks or moldy insulation, especially in attic spaces.

What to do with extra insulation?

Once the project is complete, if there is still leftover insulation, place it in a durable trash bag and drop it off at a specialized waste facility, like a building materials disposal site.

Is it possible to have too much insulation in your attic?

Too much of anything is bad, including too much insulation in an attic. Over insulating your house and tightly sealing it too much creates a vapor barrier and forces moisture to settle on fixtures inside your home (hello, water damage!).

What ruins insulation?

Moisture damage

This can occur due to leaks in the roof or foundation, inadequate ventilation, or high humidity levels inside a building. Moisture can cause the insulation material to become compressed and lose its effectiveness, leading to increased energy consumption and potential mold growth.

Is it better to insulate a ceiling or roof?

The answer to these issues may be adding insulation, but that still leaves the question of where to apply additional thermal protection to see the most benefit. While both ceiling and roof insulation will increase your home's resistance to outside temperatures, insulating the ceiling should be your priority.

What are the 10 warning signs of mold toxicity?

Although symptoms can vary, the most common symptoms seen in people exposed to mold indoors include:
  • Nasal and sinus congestion.
  • Eye irritation, such as itchy, red, watery eyes.
  • Wheezing and difficulty breathing.
  • Cough.
  • Throat irritation.
  • Skin irritation, such as a rash.
  • Headache.

Does FEMA pay for mold remediation?

As a homeowner who is eligible for FEMA assistance, you may receive funds to remove disaster-caused mold damage as part of your Home Repair Assistance award. For information about mold cleanup from the Centers for Disease Control and Prevention, visit CDC.gov/mold/cleanup.

What insulation doesn't mold?

Generally speaking, closed-cell insulation (i.e. cellular glass, phenolic, polyiso, and flexible elastomeric foam) is more resistant to mold spores than open-cell insulation (i.e. fiberglass).

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