What Do R Values Mean In Insulation?

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Generally speaking, insulation isn’t a tricky concept — You fill a space in with certain materials to inhibit the passage of either heat or sound.

But when the time comes to buy or install insulation, the specifics and jargon leave many a DIY-er shaking in their steel toe caps.

One such bit of specialist language that stops people dead in their tracks is “R-values”.

What Do R Values Mean In Insulation

It sounds like something you’d learn about in algebra or physics class, which understandably strikes fear into our hearts, but it’s not that hard to get to grips with.

In a nutshell, R-value is a unit used to measure a material's thermal flow resistance.

But it’s a little more complicated than that, so if you want more than the quick answer, stick with me, and you’ll be an insulation expert in no time.

Defining R-Values

Okay, so we’ve established that the R-value of a material is directly related to its ability to resist conductive heat flow, but what exactly does that mean?

Well, in essence, this means that the R-value of a material defines its efficacy as an insulator.

The higher the R-value of a material, the more effective it will be at keeping temperatures where they are.

For instance, a high R-value insulation in your attic will keep your house cool in summer and warm in the winter.

Lower R-value insulation won’t inhibit as much heat flow, but that’s not to say it can’t be utilized effectively; it just means we’ll need more of it, and as such, not only does an R-value inform us of the thermal resistance of a material, but round about how much will be sufficient to insulate any given zone.

What’s more, R-rating is never a constant, rather, it degrades as the insulation in question weathers temperature fluctuations, moisture, and general aging.

How Do You Calculate The R-Value Of A Multi-Layer Installation?

What Do R Values Mean In Insulation (1)

The R-value of insulation material will be given by the manufacturer and if not, should be freely available online, but what if you need to calculate the combined R-value of an installation involving multiple layers of insulation?

Thankfully, it couldn’t be easier. Simply add the R-values of each discrete layer of insulation and that will give you your combined thermal resistance value.

So, as you can see, bolstering the thickness of insulation increases R-value, but there is one exception… loose-fill insulation.

With no rigidity whatsoever, loose-fill insulation cannot support itself, and as more is added to a space, the excess weight condenses the lower levels, meaning the R-value does not rise proportionally with the thickness of the material as it does with layers of structured insulation.

But why is this the case?

R-Values Vs. Compression

It’s not just the performance of loose-fill insulation that suffers when compressed, but any form of insulation.

The only difference is that it’s impossible to avoid compression with loose-fill materials, whereas structured insulation allows for strategic compression-free insulation.

To understand why compression is the cardinal sin of insulation installations, we need to get a little scientific, so pop your lab coats on people… here we go!

Heat travels through matter by way of exciting the molecules, as when molecules start dancing, they warm up, and start bouncing into their neighbors, getting them in on the fun too.

Before you know it, you’ve got a full-blown Mexican wave of matter on your hands, and the heat radiates back into the air on the other side of the obstacle.

Now, if the matter heat is trying to worm its way through is particularly dense, the molecules are stuffed in tight together like sardines in a can, and thus, it takes very little time for heat to work them up into a frenzy and reach the other side.

But, what if the insulation isn’t very dense at all?

Well, not only does it slow down heat conduction by way of leaving more space between the molecules, it actually exhausts the thermal energy, by making conduction more of a challenge.

Therefore, less heat makes it through the insulation and into the building.

Insulation R-Value Vs. Installation R-Value

It’s also important to note that there are two separate R-values to contend with when you’re planning on insulating a room.

The one we’ve spoken about in detail already is of course the R-value of the insulating material, but even if you add up the R-value of all the layers, you won’t get an accurate R-value for the installation.

Although installation R-value takes insulation R-value into account, due to the impact of the materials that make up the wall or ceiling, it must have a dedicated value.

See, structural elements like studs and joists are more effective thermal conductors than insulation, partly due to the aforementioned density debacle, and partly because they create a direct connection from one side of the structure to the other.

Known as thermal bridging, this irritating phenomenon can be minimized during the building process by using alternating studs that do not span the entire cavity, but, unless you’re planning on a full rebuild, you’ll just have to make use of the hand you’ve been dealt.

R-Values & Radiant Barriers

Radiant barriers are becoming a popular option for those who want to develop the most energy-efficient property possible, but they don’t have an inherent R-value, and so will not raise the R-value of an installation.

It’s not that radiant barriers are ineffective. On the contrary, they work wonders. But they serve a decidedly different purpose than traditional insulation.

The job of a radiant barrier is to reflect heat rather than absorb it, so in their case, R-values become irrelevant.

Final Thoughts: What R-Value Should You Go For?

It’s impossible to say what R-value insulation would work best for you, as there are a number of variables to consider, including climate, location of the room in the property, and the type of heating and cooling systems in place.

My advice is to consult an expert in your area before you buy any materials. They’ll be able to guide you to the right sort of insulation for your installation.