Can you have too high of an R value insulation?

Author: Ayden Sauer MD  |  Last update: Sunday, June 14, 2026

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.

Can you double up R19 insulation?

If the existing attic insulation is an R-19, you may choose to add another layer of R-19. Two layers of R-19 at 6¼ ” thick will achieve a total R-value of 38. So adding an R-19 batt to an existing R-19 batt will give you a total insulation value of R-38.

Is R60 too much insulation?

According to federal Energy Star guidelines, the proper attic insulation for our climate is R60. If you already have a few inches of insulation, adding R38 to R49 insulation helps prevent heat transfer. After a point, though, adding more insulation is not cost-effective.

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.

Is it possible to over insulate a house?

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.

Busting R-value insulation MYTHS

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 possible to put too much insulation in your attic?

While over-insulated attics aren't as common as under-insulated attics, it is possible to put so much insulation in your attic that it has a negative impact.

How to check if your home is insulated properly?

One sign of good insulation is having even temperatures throughout your home. If different rooms have different temperatures – say, you freeze in the kitchen but feel too warm in your living room – that's a clear sign your house is under-insulated.

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.

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.

Can I use a higher R-value insulation?

As mentioned above, you can always increase your R-Value simply apply an extra layer of insulation over your initial layer.

What is the thinnest insulation with the highest R-value?

Thermablok® Aerogel is a revolutionary advancement in thermal technology offering the thinnest insulation available to prevent thermal and cold bridging. Classed as a Super Insulation, Aerogel has the highest insulation value of any known material with the lowest thermal conductivity value of any solid (0.015W/mK).

Does doubling insulation increase R-value?

The thermal barrier of a home should consist of a continuous layer of insulation on all sides—including the lowest floor, the exterior walls, and the ceiling or roof. Doubling the thickness of insulation will double the insulation's R-value, cutting heat loss in half.

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.

What happens if you double insulation?

By doubling the insulation layers in your loft, you increase its R-value, which in turn reduces its U-value (lower U-value is better). This results in better insulation and improved energy efficiency for your living space.

Will black mold grow on insulation?

Attic mold often appears as a thin grey or black layer on the very top of the insulation. The dimensionality of the growth is difficult to determine, as the underlying insulation presents a rough and uneven surface.

Why are there black spots on my bedroom ceiling?

This is due to the updraft of air currents created by the heat of the light bulb. As the air moves upward, it carries dust and soot particulates. As the air impacts the ceiling it quickly cools, leaving the dust particulates (and staining) behind.

Do you have to replace insulation if it gets wet?

Wet insulation will join its fibers together and create clumps in your attic. If your insulation is compressed or contaminated, then it will lose effectiveness. At that point, you will need to replace the insulation completely.

Can a house be too well insulated?

The short answer is, yes, you can over-insulate your home. While your home should be well-insulated against the cold and keep you cool during hot summer months, that doesn't mean you should cram the walls full.

How to tell if insulation is behind drywall?

Check Behind the Baseboards

Put the wood between the wall and the pry bar to avoid any drywall damage. Then you can easily pry the trim away to get access to the bottom of the wall. If there is existing insulation like fiberglass or cellulose, you will be able to see it in the gap at the bottom of the drywall.

What happens if your house is not properly insulated?

The lack of insulation in homes can lead to condensation and mould growth, creating unhealthy living environments and potentially causing structural damage. Insulation slows the movement of heat through the walls, roof, and floors, maintaining a more consistent indoor temperature.

Where should you not put insulation in the attic?

Also, when laying down additional insulation, work from the perimeter toward the attic opening. Never lay insulation over recessed light fixtures or soffit vents. Keep all insulation at least 3 inches away from recessed "can" lights, unless they are rated IC (Insulated Ceiling).

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.

What is the normal amount of insulation in an 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.

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