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R 15 Has many applications. This explains the many uses of R 15 and other facts. You will learn:

  • The best uses of R 15
  • The differences between a faced vs unfaced insulation
  • The comparison between R13 and R15 insulation in price
  • The best place to install an R15

The Best Uses of R15

Cathedral Ceilings

You typically want at least R 30 in a cathedral ceiling. However some older ceiling built with 2x6 rafters only allow for a little space to install insulation.

A good rule of thumb is, the more insulated a cathedral ceiling is, the higher the uniformity between the ceiling temperature and the room temperature.

This in turn creates a positive effect by establishing an even temperature distribution throughout the home.

And while you may have to use more R-volume when opting for lower-rated insulation, an R15 will provide the needful regulation at a pass.

But again, whether an R15 would be an ideal insulation would be dependent on your cathedral ceiling type whether it is vented or not (find that out before installing an R15).

Suppose yours was an unvented (hot roof) cathedral ceiling, you may want to first install foam insulation throughout the wood rafter to get rid of the thermal bridging before installing your foil-faced batt R15 which is then further separated from the decking with a vent baffle.

And if a vented cathedral ceiling, on the other hand, an unfaced R15 will do the trick.

At the bottom line, among others, R15 offers the best permeability rating as required by a 2x6 ceiling without attics like a cathedral ceiling.

Exterior walls

So, here's why an R15 works great on exterior walls.

If your home still feels super-warm in Summer and cold in Winter even after insulating your ceiling and adopting a proper air sealing, an R15 on the exterior wall will balance the equation.

Not only that, but an R15 is also easier to cut and work with compared with an R30 and can establish a warmer interior by protecting each room from condensation.

Finally, it offers continuous insulation, thereby cutting down the thermal bridging between the wood studs to improve your comfort whilst cutting your energy bills even lower. Yay!

Floors above unconditioned garages

A faced R15 can withstand the inevitable contamination from car exhaust, gardening supplies, solvents, paints, and other equipment used or stored in the garage than an R9 or R11 would.

Ducts generally

Sealing and insulating the ducts in your home that are unconditioned via an R15 is a more effective way to eliminate the energy losses associated with all duct systems.

Besides, given that a fewer volume of R-15 is needed to establish a high R-value, it is a more cost-effective way to insulate duct systems especially for a home that has many of them.

Basement exterior

your basement has a lot to say about the condition of your living space both in temperature and humidity. And that’s where the R-15 becomes more functional especially in the exterior of an unconditioned basement that is connected to every last one of your home’s living spaces.

An R15 on the exterior of a basement will protect the damp-proof coating from damage during the process of backfilling and likewise prevent moisture intrusion.

It will reduce temperature swings whilst serving as a foundation to the thermal mass of your conditioned space due to its thickness.

Finally, the said room area is fully conserved when an R-15 is installed on the respective basement exterior than when installed on the interior or when not at all.

The only limitation, however, is an R-15 is more difficult to install in the basement of an existing home compared to an R9.

Did I also mention the part that an R-15 can prevent insect infestation?


According to studies, most homes with insulated slabs in the United States are able to cut down heating bills by 20% or 10%.

But an R-15 insulated slab will do just more such as providing termite resistance and providing adequate heating for a discomfortably cold space.


An R-15 insulation installed during the construction stage will greatly prevent radon infiltration, insect infestation, and moisture problems especially for the below-grade rooms.

Nevertheless, putting an R-15 in place into the foundation of an existing construction can turn out impractical, expensive, and less effective.

See the next section for the highlight of the widths the R-15 comes in.

What Widths Does R 15 Come In

Basically, the R-15 comes in three widths namely:

  • 15inches
  • 23 inches

A part of doing your insulation right is knowing when to go faced or unfaced.

So to speak, in the next section, I'll stretch out the differences between the two then you can choose decisively what's good for you. Sounds great? Let's drill in.

Faced vs unfaced Insulation

The major difference between the two is that faced batts or rolls are blanketed with vapor retarder to protect the installation space from moisture unlike the unfaced counterpart.

But that's not enough for you, especially if you were a newbie, to make a guided decision between the two. Right? Take a sneak peek at the pros and cons of each below.

Pros of faced insulation

  • The integrated facing material enables easy handling and installation
  • The facing material used prevents the collection of moisture in the ceilings, floors, or walls in which they are installed
  • A great way to prevent the growth of molds and mildew in your home
  • They make insulating an existing home look easy during a renovation
  • They keep dry walls dry for longevity

Cons of faced insulation

  • As the integrated vapor retarder is mostly made with kraft paper, faced insulators are somewhat combustible. The slightest contact with an electric device or with a heating source or a masonry chimney can result in a fire hazard
  • There's a limitation to where and when you can use a faced insulation. Due to their combustion nature, places like kitchens, garages, and chimneys should not be given a faced insulation.
  • Faced batts are not an ideal add-on to an existing insulation. Here's what I mean. When an existing old faced insulation is reinforced with another faced batt or a roll that is faced to increase the existing R-value (level of energy efficiency), the chances of moisture getting trapped between the duo is increased which in turn can lead to an untimely damage of the duo.
  • Faced insulations are more expensive compared to the unfaced ones. But what really determines how expensive yours will be is the R-value of your batt or roll of choice, the geographical location of your home, and the magnitude of the space where the installation will be done.

Pros of unfaced insulation

  • They are the best for stacking. Suppose you were to increase the R-value of an existing faced insulation, an unfaced one will perfectly fit as a reinforcement without the bottleneck of moisture trapping between the old and new
  • You get to spend less in the end both for the purchase and installation costs
  • There's no restriction to where you can't use a faced insulation in your home as far as fire hazard is concerned

Cons of unfaced Insulation

  • Your contractor works harder installing them as they are more difficult to handle compared to the facing rolls with their facing
  • They don't have moisture retarder which means that water can easily creep into your walls, basement, ceiling, and floors
  • There's the high probability of having to deal with mildew and molds often than not

By now, you should already have decided on whether a faced or an unfaced one is the best for you.

Likewise, you should already know what distinction lies between an R15 and an R13. Right? In the next section, I will highlight the price difference of the two distinct rated devalue insulators.

Price Comparison R13 Vs R15

Usually, R15 is 50% above the price of R13. Nevertheless, the price difference varies from manufacturer to manufacture and the material of your insulator.

Another factor that determines price is whether you're going for an unfaced or a faced R13.

A faced R13 can be more expensive than an unfaced R15. That makes as much sense when you compare the price of a small size R15 with a bigger size R13.

But with all things equal, a 23inch × 93inch R13 has an average price range of $22-$50 whilst an R15 of the same size would cost you either $52 or $150 or anything in-between.

Where to install R15

  • Exterior walls: an R15 wall insulation on the 2x4 exterior will eliminate overheating in Summer and freezing in Winter.
  • Basements and floors: as it is much denser compared to an R13 or an R9, you have more control over mildew growth especially if your R13 has a facing.
  • Interior wall reinforcement for sound barrier: a fiberglass R15 unfaced insulation will reinforce an existing faced one without being exposed to moisture-trapping whilst still performing the job of keeping the room temperature balanced throughout your home.
  • Kitchen and Chimney: opting for an R15 unfaced insulation for your kitchen or chimney is the safest fashion to avoid overheating in those heat-concentrated spaces without an exposure to fire accidents unlike with a faced R30 or so.
  • Garage: you can keep the entire garage comfy with an R15 used throughout the whole structure including the walls, floor, and ceiling. Besides, a fiberglass R-15 can reasonably withstand the stains and fumes from your combustion without a heavy maintenance cost on your neck.


Making a good decision can be hard when it comes to choosing the right insulator for your home or office.

It gets even trickier when you're new to the whole thing and can't seem to figure out what sets an R15 apart from an R13 or where an unfaced R15 should go. I hope this helps you in making the right decision. If you need to speak to a knowledgeable person please call 424-343-6530