Should I use r30 or r38 for attic?

Author: Prof. Ernie Shields  |  Last update: Tuesday, June 24, 2025

If your attic has little or no existing insulation, you'll want to install an R-38 rated material. If your attic has 2-3″ of existing insulation, you'll want to install an R-30 to achieve a total of 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.

What is the best R-value for an attic?

The recommended amount of attic insulation can vary based on your location and local climate. However, a general guideline is to aim for an insulation level of R-30 to R-60. Here's a breakdown: R-30: Suitable for warmer climates, providing adequate insulation for moderate temperature variations.

What is R38 insulation used for?

R38: Tailored for Moderate Conditions

Best suited for mild to moderate climates where building codes allow lower thermal resistance. Commonly installed in attic floors, walls, and standard residential construction.

What insulation should be used in attic?

If you're concerned about having a positive impact on the environment, fiberglass batt is probably the best insulation option for your attic.

Can you put too much insulation in an 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.

Batt vs Blown Insulation - What's the Difference?

Is extra attic insulation worth it?

Easier to heat and cool: When you have quality attic insulation, more heat stays in your home through the winter, and less radiates down from your attic in the summer. This resistance to heat makes it more affordable to heat or cool your home to the temperature you're comfortable with.

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 thickness is best for attic insulation?

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.

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).

Should I use R30 or R38 for an attic?

If your attic has little or no existing insulation, you'll want to install an R-38 rated material. If your attic has 2-3″ of existing insulation, you'll want to install an R-30 to achieve a total of 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.

What is R30 insulation good for?

In homes with unheated basements or crawlspaces, insulating the floors with R30 prevents cold air from seeping into living areas. This application is especially valuable in regions with harsh winters, where maintaining a warm floor surface enhances comfort.

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.

What is the recommended level of attic insulation?

Warm loft insulation (Professional)

For the full recommended depth of 270mm, insulation must be installed between and beneath the rafters. You'll also need Building Regulations approval before work can begin.

Should I insulate my attic floor or ceiling?

Insulating your attic floor can create a vented attic, which is ideal for storage and not needing temperature control upstairs. Insulating the ceiling will make an unvented attic, which allows you to control the temperature for temperamental storage items, living space, and HVAC ductwork.

Should I remove old attic insulation before adding new?

Do I Have To Remove Old Insulation? Unless your insulation is wet, moldy or infested with pests, you don't need to remove it before adding insulation on top of it. ENERGY STAR® recommends that you inspect your insulation for signs of mold, mildew, moisture and pest infiltration before making this determination.

What is the rule for attic insulation?

Insulation is graded by its R-value—the higher the R-value, the greater the insulating power. If you live in a mild climate, your attic should have a minimum grade of R-38, or about 13–14 inches of insulation. If you live in a colder climate, R-49 is the minimum recommendation, or about 16–18 inches of insulation.

What is the best insulation for an attic ceiling?

5 Best Attic Insulation Options
  1. Loose-fill and Blown-in Insulation. Loose-fill and blown-in insulation are some of the best insulation options for attic spaces. ...
  2. Spray Foam Insulation. ...
  3. Fiberglass Batt and Roll Insulation. ...
  4. Mineral Wool Batt and Roll Insulation. ...
  5. Structural Insulated Panels (SIPs)

Is bat or blown in insulation better?

Batt insulation is more effective over the life of the building. It is true that blown-in insulation is considered to be more effective as a thermal barrier, however, this effectiveness is only temporary and will not last for the life of the building.

Does adding extra insulation in the attic help?

Nonetheless, adding attic insulation is worth it, and anyone should expect the following benefits: Cost savings: Using less energy has the secondary benefit of lower monthly utility bills. Energy savings: If you reduce your carbon footprint, insulating your attic can prevent heat loss and help your home save energy.

Does attic insulation need a vapor barrier?

In Most Cases, Attic Insulation Does Not Need To Provide A Vapor Barrier. The good news is that blown-in insulation should not need a vapor barrier.

Should an attic be sealed or vented?

In hot, humid locations, it may also be advisable to construct unvented rather than vented attics to help reduce the entry of moisture-laden air into the attic. In hot, humid locations, the outside air is likely to be more humid than the inside air.

Should attic insulation cover joists?

In unfinished attic spaces, insulate between and over the floor joists to seal off living spaces below.

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