How thick should insulation be for internal walls?

Author: Blaze Medhurst  |  Last update: Monday, February 23, 2026

In the walls: Typically, there is not an abundance of space inside your walls, so packing in the insulation isn't a bad idea. To get an R-value of 13 to 16, you will need four to five inches of insulation. However, if you use a more effective type of insulation, you may be able to get away with less.

Is R13 or R19 better for walls?

no, R19 will not provide better sound attenuation than R-13. In fact, just like thermal properties, it will actually provide less. What you're trying to block are airborne noises. An R11 sound batt will provide the best attenuation in a 2x4 wall compared to any of the fiberglass insulation products.

Can you put too much insulation in walls?

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.

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.

How thick should interior insulation be?

In the walls: Typically, there is not an abundance of space inside your walls, so packing in the insulation isn't a bad idea. To get an R-value of 13 to 16, you will need four to five inches of insulation. However, if you use a more effective type of insulation, you may be able to get away with less.

HOW TO INSULATE SOLID WALLS

How much better is R30 than R19?

While both types provide insulation, R30 is the better option for maximizing energy savings in areas where heat loss or gain is a major concern. For example, R19 may suffice for interior walls, but R30 is more appropriate for exterior-facing attics or floors.

What is proper insulation for interior walls?

If you're adding insulation to existing interior walls, the best option is loose-fill insulation. Available in common insulation materials like mineral wool, cellulose, and fiberglass, loose-fill can be blown into a small hole cut into your drywall, minimizing the amount of work (and mess) of the project.

What is the minimum thickness of insulation for an internal solid wall?

For internal wall insulation, you will have two options, using solid foam insulation boards with a plasterboard face, or building a stud wall and installing insulation within it. For solid boards with plasterboard facing, your options will range from about 60mm to 100mm.

What is the maximum R-value in a 2x4 wall?

A 2x4 wall cavity can be insulated from R-13 to roughly R-25. A 2x6 wall can be insulated from R-19 to R-39. Material selection, density, and cavity depth all play a role in the “cavity” R-value of a wall.

What should you not do when installing insulation?

Leaving Too Many Gaps

One of the biggest problems DIY homeowners face is leaving too many gaps in their insulation. Gaps or insulation that isn't secured correctly can leave the building structure open to air and moisture leaks. Spray foam insulation is best for reaching into small cracks and any areas left open.

What is the best thickness for wall insulation?

It is recommended to have an external wall insulation thickness of 100mm to achieve better thermal efficiency and reduce the U-value by 0.3W/m2K.

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 R19 in a 2x4 wall?

The DOE Insulation Fact Sheet (DOE/CE-0180) can be ordered from the Energy Efficiency and Renewable Energy Clearinghouse or accessed from the Internet at www.ornl.gov/ roofs+walls. Fiberglass and rock wool batts—2x4 walls can hold R-13 or R-15 batts; 2x6 walls can have R-19 or R-21 products.

Does doubling insulation double R-value?

The dip from R10 to R4 seems odd, as one would expect more R as you travel further north through the zones. Thicker is not better! Doubling the amount of insulation will double the R-Value, but so what? Doubling the insulation from R-19 to R-38 does NOT cut the heat loss in half (50%) it cuts it by around 3%!

Why is insulation so expensive?

Many factors contribute to the high cost of insulating a new construction home. Between the quality of materials, labor costs, and regulatory compliance, insulation costs can add up quickly. Investing in premium insulation like spray foam is an expensive choice.

What is the cheapest way to insulate internal walls?

Thermal lining paper is among the cheapest ways to insulate internal walls. This thick, insulating wallpaper can be easily applied directly to walls, making it a quick and straightforward solution. Costing around £10 per square metre, it effectively reduces heat loss and is perfect for smaller DIY projects.

How do I choose insulation thickness?

For domestic hot water systems use 1" thick fiberglass pipe insulation on pipes up to 2"IPS. Use 1-1/2" thick walls on pipes larger than 2" IPS. *Minimum thicknesses to meet ASHRAE 90.

What is the best insulation for indoor walls?

Rigid foam boards

They are highly effective insulation options due to their high thermal resistance (R-value) and ease of installation. These boards are particularly effective at reducing heat loss, making them ideal for homes with solid walls.

What is the most common interior wall insulation?

The most common insulation materials are fiberglass, cellulose and foam. Home insulation types include any of the above materials in the form of loose-fill, batts, rolls, foam board, spray foam and radiant barriers.

Do I need a vapor barrier on interior walls?

Not every wall does. A vapor retarder is a material used to prevent water vapor from diffusing into the wall, ceiling or floor during the cold winter. Whether or not you need a vapor retarder hinges on three main factors your climate, your home and the location of the wall you're insulating.

Is r13 insulation good for interior walls?

For homeowners in moderate climates, R-13 often provides sufficient insulation to maintain comfortable indoor temperatures while keeping energy costs reasonable. However, those in extreme climates might want to consider higher R-values or additional insulation layers.

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).

Should you use faced or unfaced insulation in a crawl space?

Faced insulation is ideal for spaces that have no existing insulation, such as exterior walls, attic ceilings, crawl spaces, and exterior basement walls. Please note that the proper way to install it is to have it installed facing outward or towards the person installing it.

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.

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