How Thick is R30 Insulation? A Brief Guide

R30 is one of the standard R-values of insulation, which is a measure of the resistance offered by a material to the conduction of heat. Insulation is rated R30 if it can reduce heat conduction by 97%. Since the thermal conductivities of different insulation materials are different, the thicknesses required for them to achieve R30 rating vary accordingly.

Given below are the R30 insulation thicknesses for different insulation materials;

Insulation Material Type R30 Insulation Thickness
Fiberglass 8.25 inch
Open-cell spray foam 9 inch
Closed-cell spray-foam 4.25 to 6 inch
Foam Board insulation (Rigid foam) 7.5 to 8.33 inch
Blown-in fiberglass 12.4 inch
Blown-in Cellulose 9.3 inch
Rock Wool – blown in 10.9 inch
Rock wool batt 8.87 inch
R30 insulation thickness for different types of insulations

The thickness or depth of R30 Insulation is determined by the properties of the material used for the insulation and will be discussed later in the article. The thermal conductivity of different insulation materials will differ as influenced by the properties of the material and the path length or thickness of the material through which heat is conducted.

An R30 insulated attic ceiling
An R30 insulated ceiling

Before delving deeper into the thickness of R30, it is imperative to discuss parameters describing the R-value. We will look at what it means and in which climate zones we can utilize R30 insulation.

The R-value and Meaning of it

The R-value as in R30 is descriptive of the absolute thermal resistance of the insulation in square meter kelvin per watt. It indicates the material’s resistance to heat conduction through its thickness or depth. Thus, a higher R-value will indicate more resistance to heat flow, while a lower R-value will indicate less resistance to heat flow. Therefore, the R-value is inversely proportional to heat flow, and insulation with a higher R-value will insulate your home better than insulation with a lower R-value.

In addition, insulation with a higher R-value will ensure more energy efficiency, while insulation with a lower R-value will reduce energy efficiency. This is because the amount of energy used for heating increases as the R-value of insulation decreases and will decrease as the R-value gets higher. Therefore, adequate insulation with the correct R-value will reduce your energy bill because less heat is lost by conduction through the insulation, leading to less heat needed.

It is important to note that the R-value is only a measurement that takes conduction into account and not heat loss through convection or radiation. Adding foil-faced kraft paper may reflect the energy back to its origin and stabilize the temperature inside, leading to an increased R-value of the insulation.

What is R30 Insulation, and Where do We Use it?

R30 insulation can minimize conductive heat loss out of your home by 97 percent, and this will make your home 97% hotter than without insulation, saving you a lot of money on your energy bill.

R30 insulation is the minimum insulation recommended for an  Attic from climate zone 1 to 3, while it can be used in cathedral ceilings in all climate zones across the USA. It can be used as maximum insulation in climate zones 4 – 8 of the USA for floors.

The thickness of R30 Insulation will vary in accordance with the products used to form the insulation, and it may vary from 6″ up to 12.4.”

Different Types of Insulation Materials and Thickness Requirements to be Classified as R30 Insulation

Fibreglass Insulation

Bats of Fiberglass insulation are usually 8.25″ thick to attain an R-value of R30. Initially, it might be 10″ thick to compensate for a fair amount of compression during handling and installation. 

Fiberglass insulation is the fluffy pink bats that we see in home improvement stores, and people would generally relate that to insulation. Fiberglass insulation is made out of 80% recycled glass and is naturally soundproof as well. These fiberglass bats come in a variety of R-values for the insulation of different parts of homes in different climate zones.

The fiberglass insulation is available in batts of 16″ and 24″ width, which coincides with the spacing of framing members in a wall. That ensures that the batts can be fitted snugly into the spaces between framing members. Spacing between framing members might be slightly less than 16″ or 24″, but that will ensure that batts can be inserted snugly and well sealing between members. Care must be taken that the batts are not compressed since that will limit the R-value for the compressed area.

However, it is essential to measure the spaces between the joint spacing of the area on which you want to install insulation. Then, wherever custom sizes of insulation are needed, they can easily be cut into desired sizes with a sharp utility knife. 

Spray Foam Insulation

Spray foam is a powerful method whereby you can insulate your home, but you need to distinguish which spray foam you are going to use. There are two types, and each one has a different purpose and must be used to fulfill its purpose. Both types are discussed below, each with its own thickness to attain an R-value of R30.

1. Closed Cell Spray Foam

Closed-cell spray foam must be applied to a depth or thickness of 4.25″ to 6″ to attain the resistance to conduction as required of R30 insulation. Closed-cell polyurethane spray forms a closed-cell when sprayed that eradicates the penetration and build-up of moisture inside the foam that will cause mold growth and negate the R-value. In addition, due to the high resistance of closed-cell spray foam moisture build-up, mold growth and bacterial growth are eliminated, allowing insulation to last longer.

Closed-cell spray foam is also denser and ideally situated to insulate appliances and buildings. In addition, it forms a water vapor barrier between two adjacent spaces without mold growth and even strengthens the walls of buildings. Closed-cell spray foam uses a chemical compound to blow, and that might leave an odor for a while, but it quickly evaporates.

2. Open Cell Spray Foam

Open-cell spray foam will expand after spraying, making it easy to use in hard-to-reach spaces. So that hard-to-reach nooks and crannies can easily be reached and filled with spray foam. On the downside, the expansion of the open-cell spray foam makes it less dense and thus not as water-resistant and effective as closed-cell spray foam. Because of its decreased density, a 9″ deep or thick layer of insulation must be applied to ensure that insulation adhering to R30 standards is reached.

The lighter quality of this foam supplies less moisture resistance, does not act as a support for buildings, is less soundproof, and is permeable to air and moisture. The lighter composition with expanding characteristics was deliberately chosen for the specific purpose it yields. It is to be used in difficult-to-reach areas where the expansion will ensure cover. So if you want to insulate a building grab closed-cell spray foam and use the open-cell spray foam only for that hard-to-reach areas.

Foam Board Insulation (Rigid foam insulation)

Foam boards are typically rigid sheets of polystyrene or polyurethane and are used as insulation for buildings. Foam board with thickness or depth between 7.5″ – 8.33″ will be adequate for R30 insulation. Commonly they are not seen or used in residential buildings but are instead used in commercial buildings at large. However, they can provide insulation in cases where continuous code insulation is required and are typically used in combination with external cladding systems.

Cutting these boards using a hot knife is a tedious, time-consuming job. Although it might seem like nice insulation for a ceiling in residential situations, it is definitely not recommended. Currently, there is no foam board available with an R30 rating.  

Fiberglass Blow-in Insulation

With blown-in insulation, either fiberglass or cellulose is blown in using a pneumatic sprayer. Cellulose insulation is seen as a more sustainable option because recycled paper fiber is used. It is an excellent method to insulate all those hard-to-reach spaces as encountered in an attic.

This is the ideal type of insulation to install from the start but really makes things easy when used on top of existing insulation to upgrade the R-rating in-ceiling installation. To reach an R30 rating, you will need a layer of 12.4″ blown-in fiberglass and 9.3″ of cellulose.

Working with blown-in fiberglass insulation has its dangers. It is of the utmost importance that you take safety precautions to escape irritations of the eyes, respiratory system, and eyes. Wear a long-sleeved shirt, long pants, boots, as well as a face mask and safety glasses to protect yourself from harm.

By covering any exposed skin with Baby Powder, you might nullify irritation of those areas. If your skin, however, does become irritated, take a hot shower afterward. Hot water will open your skin pores and will allow the fiberglass to penetrate your skin further.

Rock Wool Blown-in Insulation

Rockwool is mineral wool that is inorganic and can be used as thermal insulation in attics, wall cavities, and ceiling cavities with a depth or thickness of 10.9″ to attain R30. It is made of rock, furnace slag, and other organic materials. 

It is a porous material that traps air while it is fire resistant with acoustic barrier properties that makes it an ideal material for insulation purposes. It can be used by any construction type and in any climate zone. Attention must be given that the area where it is applied constitutes enough space to reach the required depth or thickness in order to attain R30.

Further reading: Rockwool R value

Rock Wool Batt Insulation

Rock wool batts can be used in exterior wood and steel framed buildings as insulation at a thickness of 8.87″ to attain an R30 value. It is also used on exposed floors, attics, and crawlspaces, seeing that it is water-resistant and does not contribute to the formation of mildew, fungi, or mold. That will supply you with insulation in your basement or crawl space that won’t need replacement because of mold, mildew, and rot.

Rock wool is fire resistant and provides excellent noise reduction to create quieter, more productive work environments while lightweight and easy to install. The edges of the batts are elastic to ensure that bats snuggly fit into spaces between joists as well as wooden and steel frame structures.

Charles John

A novice DIYer who learns about home ventilation. I am a mechanical engineer and have a basic knowledge of HVAC systems but I learn continuously to make myself the best blogger in that space.

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