Home Comfort Insulation

The Homeowner’s Guide

to Attic Insulation

How Attic Insulation Works

Your attic insulation is the thermal barrier between your indoor living space and your home’s attic, keeping the heat out in the summer and holding it in during the winter.

You can think of your attic insulation working by soaking up heat like a sponge soaks up water. The same way that a thicker sponge can soak up more water before it starts leaking through, deeper insulation can soak up more heat before it starts leaking through your home’s ceiling.

A well-insulated attic Will give you:

Cooler Summers

Your attic temperature regularly climbs above 160F on a sunny summer day. A well insulated attic stops that heat before it can make it down into your home, giving your AC the chance to keep you cool all summer long.


Warmer Winters

Your furnace does a great job at pumping heat into your home, but if there’s nothing holding that heat in it’ll have to run constantly to keep you warm. Attic insulation holds the heat in where you want it instead of letting it pass up through the ceiling.


Lower Energy Bills All Year

When your heater and AC have attic insulation to help them do their job and don’t have to run constantly to keep you comfortable, you save on your energy bills year-round.


You Have Questions?

We Have Answers.

What does “R-Value” mean?

The R-value of a material is a measure of its thermal resistance – you can think of it as the “insulating power” of the material. The higher the R-value, the greater the insulating power!

How much attic insulation do I need?
What R-value should my attic be?

We recommend a minimum attic insulation R-value of R-49. This is achieved by a minimum final insulation depth of 16.75″ with the material that we typically install when insulating attics (Owens Corning PROPINK L77 Loosefill Fiberglass).

This recommendation is based off of the International Residential Construction Code (IRCC) recommendation for our climate zone here in the Boise area. We’ve found that an R-49 is the best balance of upfront cost and long-term efficiency and comfort for most homeowners we work with (and the building science data backs this up). If you’re planning on living in your home for more than 7-10 years it’s worth considering bringing your attic insulation up to R-60, which is going to yield the best long-term savings in energy efficiency and is a sure way to keep your home comfortable & efficient year-round.

The minimum R-value required by most local building codes in the Boise area is R-38. This lower requirement is due to builders having a heavy influence over which new building codes get adopted each year, and if you know how most builders operate then you know they’re always looking to cut costs wherever possible. While you can usually get by with R-38 attic insulation, it’s likely that your AC & furnace will struggle to keep your home comfortable and your energy bills will be higher than necessary year-round.

What’s more important,
insulation depth or R-value?

R-Value! Insulation depth means nothing without knowing the R-value of the material.

For example, when installed to manufacturer’s specifications blown-in fiberglass insulation produced by CertainTeed requires a minimum installed depth of 18.25 inches to achieve an R-49 while Owens Corning’s blown-in fiberglass only requires a minimum depth of 16.75 inches.

What is the best type of attic insulation?
Is fiberglass or cellulose insulation better?

Blown-in fiberglass insulation is a much better choice than cellulose for attic insulation in terms of both upfront cost and long-term performance.

This is a long-standing debate in the insulation industry that takes a lot more than a couple of lines to fully explain, but the short answer is that improvements in the material science of fiberglass insulation production and the deterioration of the source material quality for cellulose insulation (recycled newsprint) means that modern fiberglass insulation is a much better choice than cellulose in the vast majority of cases.

What type of attic insulation do you install?

We install blown-in fiberglass and fiberglass batt insulation.

Is batt/roll or blown-in insulation better for my attic?

Blown-in insulation is almost always a much better choice than batts when insulating an attic for two main reasons:

  1. More Even Coverage – batt insulation leaves gaps around attic framing, pipes, and wires, leading to thermal bridging and resulting in a lower effective R-value than the even, consistent coverage achieved by blown-in insulation
  2. Lower Labor Cost To Install – properly installing batt insulation requires a lot of time spent cutting material around framing, wiring, pipes, and vents while blowing in insulation is a much more routine process
How long does it take to insulate an attic?

In most cases we can complete an attic insulation project in 4-6 hours. The time it takes to insulate an attic ultimately depends on the size and complexity of the space, but you can typically expect us to be working in your home for about half a day.

Have a Question We Didn’t Answer?

Wondering How Attic Insulation Is Installed?

Here’s How We Insulate Your Attic

The Right Way to Insulate An Attic

6 Key Points To Remember When Installing Attic Insulation

All attic insulation installs are not created equal – these are the 6 key points we keep in mind when insulating your attic.

1. Air Seal First (whenever possible)

Insulation is a great thermal barrier but does very little to stop air flow, making air-sealing electrical, plumbing, & duct penetrations in your attic floor, along with every wall top plate, a crucial step in your home’s attic insulation system. Local building code started requiring these places to be air sealed in homes built after 2006, but modern garages and older homes are almost never sealed. Whenever we’re installing insulation in an empty attic, this is the first step of the process.

Effectively air-sealing the attic floor isn’t possible if you already have insulation in your attic, In this case, air-sealing your home from the inside is the way to solve the problem.

2. Keep Your Soffit Vents Open

The vents around the soffit of your roof (known as soffit vents) serve as the intake for your attic’s ventilation. We install baffles between your roof’s trusses at each soffit vent to keep them clear of insulation and make sure your attic ventilation stays open to airflow.

3. Install to the True R-Value Desired

A material’s R-value is a measure of its thermal resistance – you can think of it as the “insulating power” of the material. Each brand of insulation needs to be installed to a specific depth and density (usually measured in bags of material per 1000 square feet) to reach a target R-value. This combination of depth and density for each R-value is known as a material’s coverage chart. Find more information for the material we install, Owens Corning L77 Loosefill Fiberglass, here.

It’s easy to accidentally (or intentionally) “stretch” the coverage of blown-in insulation by over-conditioning it, which is just industry speak for making it extra fluffy. This results in insulation that looks to be the right depth but isn’t dense enough, leaving you with less R-value than you want.

Installing insulation rulers throughout your attic, installing above the minimum required depth, and keeping track of how many bags of insulation we install in your attic makes sure we’re providing a final product that provides the R-value you asked for or greater.

4. Build an Access Barrier

The last thing you want is to get covered in a shower of insulation when you open your attic access. That’s why we install a barrier around the edge of every attic access. This barrier also let’s us install your attic insulation to its full-depth all the way up to the edge of your attic access.

We typically construct these access barriers out of the same heavy-duty cardboard that we use for baffles (have you seen the price of lumber lately?). We do also offer an option to upgrade to a solid, framed-in plywood access barrier for anyone who plans on getting into their attic often and wants the extra support.

5. Insulate the Access Cover

If you’re insulating your attic it should be your entire attic, including the often ignored piece of drywall that serves as the cover for your attic access.

We insulate every attic access cover with a piece of batt insulation that matches the R-value of the rest of your attic. This gives your entire attic a consistent insulation level without any gaps or low points, without getting showered with insulation when you open the access.

6. Double Check Your Vents

We install baffles to keep your intake vents clear, but it’s always a good idea to take an extra step to make sure that nothing is blocking them – whether it be stray insulation that found its way past the baffles during the install or decades of dust buildup that has never been cleaned. That’s why we blow out every soffit vent from outside of your home once your attic insulation install is complete, ensuring your attic ventilation is functioning at its best.

Why Choose Us for Your Attic Insulation Project?

See What Our Past Customers Have to Say

Too Much Jargon?

Here are a few terms to help you understand the language around attic insulation.

R-Value

A material’s R-Value is a measure of its thermal resistance. In this context, you can think of it as the “insulating power”, with higher R-values providing greater insulating power.

Soffit Vents

Soffit vents are the vents installed on the underside of a roof ’s eves. They serve as the attic’s intake ventilation in most modern homes.

Baffles

A baffle is a barrier installed at soffit vent openings to maintain an open airflow channel for intake ventilation. Baffles can be made of plywood, cardboard, plastic, or foam.

Blown-In/Loosefill Insulation

Blown-In or Loosefill insulation is the fluffy insulation material typically seen in attics. This type of insulation requires an insulation blower to be properly installed.

Batt/Rolled/Blanket Insulation

Batt insulation is the large, rectangular pieces of insulation often seen in walls and floors. This type of insulation can be installed by hand, making it a popular choice for DIY projects.

Air Sealing

Air sealing prevents airflow between unconditioned spaces (your attic, crawlspace, and the outdoors) and conditioned
spaces (inside of your home) by sealing air leakage points in the building envelope. Air sealing a home is typically accomplished using canned spray foam and/or caulk.