How thick should insulation be in an attic?

Author: Matilda Volkman  |  Last update: Monday, March 9, 2026

Insulation levels are specified by R-Value. R-Value is a measure of insulation's ability to resist heat flow. 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.

Can you put too much insulation in attic?

While loft insulation is an effective way to improve energy efficiency and reduce heating costs, over-insulating can lead to several potential issues. Firstly, over-insulation can lead to poor ventilation in the attic, which can cause moisture buildup and increase the risk of mould growth.

Is R19 or R30 better for an attic?

Yes, you can use R19 insulation in an attic, but whether it's suitable depends on a few factors: Climate Zone: R19 insulation is typically appropriate for attics in moderate climates. In colder climates, higher R-values (like R30 or R38) may be recommended to effectively prevent heat loss.

Should I remove old attic insulation before adding new?

Yes, it is generally advisable to remove old attic insulation before adding new insulation. Here are some reasons why: Moisture and Mold: Old insulation can retain moisture, which may lead to mold growth. Removing it allows you to inspect for any signs of water damage or mold that need to be addressed.

How often should insulation in the attic 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.

Attic Insulation and Ventilation

Do you need ventilation in attic after you insulate?

At first it may seem odd to add insulation for warmth and then purposely allow cold air to enter the attic through vents, but this combination is the key to a durable and energy-efficient home.

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 is good in the 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.

Should attic insulation be faced or unfaced?

You can use faced or unfaced batting when installing between the roof rafters of finished attic spaces. When using paper or plastic batting insulation, that moisture barrier should face outward toward the attic space. Even if the attic space is unheated, it's typically warmer than the outside air in winter.

Is it OK to use R19 insulation in attics?

You will want to bring up your attic up to R-38:

If your attic has 5-6″ of existing insulation, you'll want to install an R-19 to achieve a total of R-38.

Can you stack insulation in an attic?

Blown-in insulation is often installed in attics and other tightly enclosed spaces. If blown-in insulation was previously installed in one or more areas of your home, it is perfectly acceptable to also add rolled insulation. There is one caveat, however. You need to avoid faced insulation.

Is R60 attic insulation worth it?

If the federal recommendation is R60, then you can save yourself plenty of money on energy bills and HVAC repairs by having a minimum of R60 installed. This can be any combination of batts and blown-in insulation.

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).

What is the lifespan of attic insulation?

Conclusion. Attic insulation can last 80 to 100 years, though it loses its energy efficiency benefits with time. Certified attic specialists' professional advice is to upgrade it every 15 years to ensure that it is still performing the job.

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 do I know if my attic is insulated enough?

If your home, or upper floor, is too hot in the summer and too cold in the winter it is likely that you have insufficient attic insulation. If a visual inspection of your attic identifies that the insulation is level with or below the attic joists – you need more insulation.

Can you put new insulation over old insulation in the attic?

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.

How much will attic insulation reduce my heating bill?

On average, you can save up to 20% on your home's heating and cooling costs or up to 10% on its total energy costs by adding insulation to attics, floors, crawl spaces, and accessible basement rim joists, and by reducing unwanted air leaks all around your house.

What is the most effective attic insulation?

Cellulose is an eco-friendly and cost-effective insulation for attics. Fiberglass and mineral wool are also popular choices because they are good at keeping heat in or out and resist moisture and pests. Special equipment blows the loose-fill material into the attic spaces, ensuring it covers everything evenly.

Should I use batt or roll insulation?

If you prioritize easy installation while also ensuring affordability, installing roll insulation would be a smart choice. However, if you want a thicker alternative and wish to fit the insulation in hard-to-access areas, batt insulation would be your best bet.

How deep should blown-in insulation be in attic?

To achieve an R-value of 38 to 49 in your attic, you should aim to install 11 to 14 inches of blow-in cellulose insulation.

Should attic insulation be on roof or floor?

Should You Insulate the Attic Floor or Roof Deck? If you are looking for an insulation upgrade that you can see (on your energy bill) and feel (in a home that is more comfortable), we recommend insulating the attic floor, and using radiant barriers on the roof deck.

What to do before blowing insulation in attic?

Before blowing in your insulation, you'll need to create a barrier to keep the insulation from falling into areas where you don't want it, like your walkway or down the attic hatch. You can use a piece of rigid foam and attach it with cap nails.

What happens if you don't have enough insulation in your attic?

As energy efficiency moves to the forefront of priorities for homeowners and buyers, attic insulation has become increasingly important. Homes that lack adequate insulation in attics are at risk for a range of expensive and irreversible impacts like water damage and heat or cold air loss.

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