R-Value For Garage Insulation? (One Easy To Understand Guide!)

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Winter is here. Temperature outside is dropping. Your garage heater is working harder to keep you warm and comfortable. Maybe you need to beef up the garage insulation. As you begin to shop for insulation you keep coming across the term “R-value for Garage Insulation”.

But what is “R-value for Garage Insulation”? Are you confused? Don’t worry. You are not alone!

R-Value for a Garage Insulation, is a measure of the “resistance to heat flow”. The higher the R-Value, greater is the “resistance to heat flow”. 

In this post I will explain about the science of heat transfer and what R-Value for a Garage Insulation means. I will cover its importance for all sides of the garage; the door, the walls, the roof and even the floor.

What is R-Value for Garage Insulation?

Heat behaves just like water. Water flows downhill. From the mountain top to the sea. That is, from a higher level to a lower level. Right? Similarly heat flows from a higher temperature level to a lower temperature level. From the warmth of your garage to the freezing cold outdoors.

Now, how do you stop the water from flowing downhill? You build a dam. But you do not build a dam with something porous like sand bags. That is not so effective. A lot of water would still leak out. You use something more solid, like a thick concrete wall.

So when you want to stop the garage heat from escaping to the cold outdoors, you have to use insulation. Some materials, like fiberglass wool are much better insulators than say steel or a concrete slab. In other words, some materials have a higher “resistance to heat flow” than others.

That’s all there is to R-Value for garage insulation (or for that matter any insulation). R-Value is a measure of the “resistance to heat flow”. The higher the R-Value, greater is the “resistance to heat flow”. A material, a door, a wall with higher R-Value is simply better insulation. 

How does a garage lose heat?

I talked about heat moving from a high temperature zone to a low temperature zone, just like water flows downhill. Heat does it in three ways

• Conduction
• Convection
• Radiation

Conduction is the process when heat moves from the high temperature zone to the low temperature zone through the solid material between the two zones.

Convection is the process in which the air in contact with the high temperature zone moves and takes the heat away to the low temperature zone.

For example the heat from the garage heater will be carried by the air in the garage to the colder garage wall. This is convection. The garage wall then dissipates the heat to the cold outdoors. This is conduction.

Radiation is the process when the heat moves from the high temperature zone to the low temperature zone through electromagnetic waves such as visible light, UV rays and infrared rays.

The best example of heat transfer by radiation is the heat earth gets from the sun. There is no conduction or convection involved. The heat transfers across vast empty space by radiation alone.

Heat loss due to radiation is not a factor when we talk about garage insulation. The most important factor is conduction. This is the reason we have to talk about R-Value, when we talk about garage insulation.

The six sides of a Garage

Like any room a garage has six sides, i.e. the four walls, the floor and the ceiling. Except that the garage door is so big that it takes up most of one wall. The garage door is also exposed to the outdoors. One of the other three walls is also likely to be exposed to the outdoors.

So to ensure that the entire garage is properly insulated, we must ensure that each side of the garage is properly insulated; namely

• Garage Door (exposed to outdoors)
• Garage Wall (exposed to outdoors)
• Garage Walls (attached to living space in the house)
• Garage Floor (exposed to ground below)
• Garage Ceiling (exposed to outdoors or attached to an attic or living space in the house)

R-Value for Garage Doors

New Garage Door

Are you in the market for a new garage door? Then one of the specifications that you have to look out for is the R-Value.

Garage Doors can come as: 

Single Layer

A Single Layer Garage Door has just one layer of the garage door material, say steel. There is no insulation.

Double Layer

A Double Layer garage door has a layer of insulating material such as polystyrene foam board as a backing to the outer steel sheet. The foam board has a vinyl layer on the inner side of the garage door, which forms both a decorative and a protective layer.

Triple Layer

The Triple Layer is basically a double layer with an additional layer of steel sheet on the inside. This is obviously the best insulation you can get. This also makes the door very strong and durable.

Fortunately most manufacturers give you several choices, which include non-insulated doors and doors with different degrees of insulation. The degree of insulation is indicated by the R-Value of the garage door.

The Amarr Designer’s Choice – the ultimate protection. With triple-layer construction and superior insulation R-value of 13.35 or 19.40, these durable low-maintenance doors give you the ultimate in quiet operation and energy efficiency.

Existing Garage Door

On the other hand, it is possible that you want to add (or change) insulation on your existing non-insulated garage door. The easiest and the best way to do this is by using one of the garage door insulation kits available.

There are two popular garage door insulation kits.

The first uses panels made of Expanded Polystyrene (EPS) which can significantly reduce heat transfer by conduction. The garage door insulation kit from Matador, available on Amazon, comprises of 8 high-impact polystyrene laminate panels 23. 25″ H x 54″ W x 1.25″ thick.

Matador Garage Door Insulation features an R-value of 4.8 at 75 degree Fahrenheit.

The second uses panels that are a lot more flexible. They are made by sandwiching fiberglass insulation wool within a tough, washable white vinyl facing on both sides. The garage door insulation kit from Owen Corning, available on Amazon, comprises of 8 insulating panels 22″ H x 54″ W x 2.25″ thick.

Owens Corning Garage Door Insulation Kit features an R-value of 8.

R-Value for Garage Walls

Insulating garage walls may not be on top of your mind when you think about insulating your garage. A lot of attention goes to insulating the garage door. It is understandable. A garage door is large (often 30% of the house frontage) and exposed to the elements. 

However, the garage door is only one side of the garage. The walls are the other three sides. Most often one of those three is also exposed to the elements. You need to insulate that one just like the door.

But you also need to insulate the other two walls, even though they are adjacent to the home living space. You may use a lower R-Value for insulation though. It will help reduce home energy costs and improve soundproofing.

Insulation Material for Walls

There are three commonly used materials and these are placed between the wall (brick, cinder block or concrete slab) and the drywall or equivalent (cement block, plywood or OSB). These are:

Insulation Batts or Rolls

Insulation Batts can be made from any insulating material. Typically they use fiberglass but other types of material such as cellulose, mineral wool or natural fibers can also be used.

Standard fiberglass batts have R-values ranging from R-2.9 to R-3.8 for every inch of thickness.

Owens Corning R19 15″ 93″ Unfaced 10 bags of Fiberglass Wall Insulation 775 SF available at Amazon has a R-19 R-value because it is 6.25 in thick. The Dimensions are R-19 x 15 x 93 by 6.25 in Thick or Deep Making it Ideal for R-19 x 15 x 93 Construction.

Fire Resistant Rigid Foam Boards

Fire Resistant Rigid Foam Boards are rigid panels usually made out of 

• Expanded Polystyrene (Styrofoam) – R-values that range from 3.6 to 4.2 per inch
• Extruded Polystyrene – R-values of around 5.0 per inch
• Polyisocyanurate – R-values that range from 6.0 to 6.5 per inch

For the best in this category check out ROCKWOOL COMFORTBATT. ROCKWOOL stone wool insulation comes in R13, R21, and R38 thermal values.

Spray Foam Insulation

Spray Foam Insulation is created by injecting two liquid chemicals from a spray gun which react to form a foam. The foam expands rapidly and will fill up every nook & cranny. It then hardens to create a very strong air barrier.

Spray Foam Insulation is extremely energy efficient. However, in my opinion, it is an overkill for a garage wall.

R-Value for Garage Floors

Even more than the Garage Walls, the Garage Floor gets totally neglected when it comes to garage insulation. But for a typical two car garage, the floor is 27% of the total area of the six sides of the garage.

The garage floor is funneling the garage heat and your money, down into the cold, damp earth below every night.

Installation of an insulating subfloor is your solution.  I recommend that you install DRICORE Subfloor R+ Insulated Panel, with Air Gap Technology from Amazon. They have an R-value of 1.4 which insulates and makes the garage floor feel warmer, There are some additional benefits too!

• Air Gap Technology helps protect against moisture, mold, mildew and small water leaks
• Softens finished floors against hard concrete
• Strong enough to support up to 6,642 lbs. per sq. ft. 
• Tongue and groove design makes installation fast and easy

Insulating the Garage Ceiling

Having come so far, you can not stop. You have to insulate the ceiling above your garage. And there is a good reason to do that too!

So what happens to the warm air in your garage? Remember what the science teacher at school told you. Hot air moves up. That’s how hot air balloons work. Right?

Now let us say you have an attic above your garage. During winter your garage heater is busy heating up your garage. But unfortunately a lot of the warm air is just going up and heating the attic. You do not want to waste your money heating up an attic, if you just store some junk there!

On the other hand if you are using the room above the garage as living space, that space is getting pretty warm in summer. The air conditioner in that room has to work extra hard to keep the room cool.

To cut the long story short, you should insulate the ceiling of your garage for complete garage insulation, especially if you want a climate controlled garage.

You can opt for one of the following insulation materials:

• Fiberglass Rolls
• Fiberglass Batts
• Blown-In Insulation

Attics require very high R-Value of insulation, so make sure you get enough thickness or layers.

What R-Value do I need?

To find out you must first determine the climate zone your home falls in using the map below:

Source: Home Depot

Want to know even more? Then download this PDF from National Association of Home Builders (NAHB).

Thank you very much for reading the post. I do hope you found it informative and useful.