How to Prepare an Attic for Blown-in Insulation

Blown-in insulation on attic floor.

Learn how to get your attic prepared for blown-in insulation with our instructional guide. It is a crucial part to achieve optimum energy savings and cut your energy bills.

Looking for a challenging DIY (or, at least, partial-DIY) home project? Not falling through the attic into the living room or onto the dining room table challenging enough for you?

Well, installing blown-in insulation in the attic may be just the thing.

As with any home-improvement project, advance – and proper – preparation is key.

  • Task #1: Cellulose, fiberglass or rock wool? There are cost, installation and efficiency considerations for each. Keep reading to find out more.
  • Task #2: Given the job of installing blown-in insulation in attic encompasses tasks that range from fairly straightforward to complex, you need to make a rational decision about how much of the job you’re going to take on yourself and how much is going to require a professional contractor.

To help you make those decisions (and to ensure you correctly assess your own abilities and only take on those things you actually can accomplish), here are some thoughts, recommendations, and warnings about how best to prepare attic for blown-in insulation.

Sweat the small stuff? Yes, sweat the small stuff.

Attic corner with dormer and insulation.

Understanding how to prepare attic for blown-in insulation is not exciting, but get organized first. It’s well worth it.

  • Conduct a self-analysis. Compile a really good list of what you need – and are capable of doing – for your part of the job. And be willing to get a professional for the other parts of the job.
  • Measure the space: Installing blown-in insulation in the attic is a big job. You are going to need to put the scope of the job into context to make some of the decisions that will be coming up.
  • Write down the supplies – and equipment — you’ll need: caulk, expanding foam, flashlights, kneepads, dust masks, blower machine, hose, safety glasses; shop vacuum; power stapler; utility knife. Figure out the budget.
  • Access contact information: Get the names, addresses and contact information for a licensed professional contractor who (when you actually get around to scoping out the full job) you probably are going to want to hire for certain parts.
  • Research the tax credit situation: Get a good understanding of whether you might qualify or not before you start making financial decisions. This is your opportunity to optimize your investment.
  • Understand local requirements: Look into local building codes for recommended R-values and vapor barrier requirements. This information will help you with the cellulose-vs.-fiberglass-vs.-rock wool question. While you are at it: ensure your electrical wiring is up to code. If it isn’t, call an electrician. Don’t put it off!
  • Attic access? Garage or in-house? This can be a messy job. The location of the hatch leading into the garage is a big part of that. How much are you willing to put up with?

Easy does it! Don’t create a non-functional space.

While you are making your checklist, think about this: How do you want your attic to look, and function, after the job is complete?

  • Are you going to use it the same way you use it now?
  • Boxes, bags, and garment bags in no particular order?
  • Are you going to consider some built-in storage space?
  • How accessible does it need to be? How frequently are you (and is it only you?) going to be going up there to get something?

Two things to consider:

  • You need to maneuver up there when you are completing the job. Think about putting in a plywood catwalk (even a narrow one) in the beginning so you don’t get caught off-guard later on.
  • In all likelihood, you ultimately are going to need to put a permanent floor over the blow-in insulation because of the height of the additional insulation. What does that mean regarding maneuverability in the new attic? Is headspace affected?

You’re going to want to show off your work after you’re done. Clean it up while you are up there.

Brown fiber blown-in attic insulation.

OK, OK. You are going to find diversions along the way that will impact your progress. Your high school yearbook probably is going to eat up some time … as will the boxes of photos your parents gave you when they downsized from their house to an apartment. The Christmas tree ornaments over in the corner are going to be a dilemma because you know they will be going back upstairs after you finish.

But the bottom line is this: this is a great opportunity to clean up and throw out. Actually, it’s more than an opportunity as the job requires it.

And as you get it cleaned up, remember …

Air leaks are your enemy. Plug them up before you do anything else.

Here’s the first thing you need to understand: You may do what appears to be a perfect installation of the insulation, but optimal energy efficiency requires successful sealing (which, let’s face it, is what you’re after … well, after proving to yourself that you can successfully balance and move across attic joists).

Where you should focus: on the open spaces and other protrusions through the ceilings. Hint: turn on lights throughout your house. Yes, everyone. Then, up in your dark attic (be careful!) look around for the light. Hello, electrical wiring. Air vents.Recessed lighting. Ductwork. Skylight passages. Plumbing pipes. That’s where the air is moving in and out of the house.

  • Use caulk in smaller spaces or spray expanding foam in large gaps to plug the openings.
  • Wrap pipe sleeves around your water lines. Make sure your bath vents exhaust outside.

Don’t overdo it, however. Here’s a critical thing you need to know: Although it is good to stop the back-and-forth airflow, healthy living (not to mention the functioning of your furnace, gas stoves and fireplaces) demands that you do have some fresh air. Without it, you could create a hazardous situation.

Take the time to make all the repairs.

Contractors repairing the house roof.

Sure, you want to get to the point where you’ve got the hose resting against your hip and you’re spraying cellulose. Who doesn’t? But you – or your contractor – has to get through this painstaking initial repair phase first. And, you can bet that new staple gun you just bought on this: the number of little jobs that make up the repair list is ultimately going to be way larger than you anticipate. And the adjective “little” is the wrong word.

So you’re going to want to cut corners or try to put some of them off.

You can’t.

  • You need to make these repairs, or have them made, to shore up everything before starting the installation.
  • And they need to be done – obviously– before several inches of cellulose insulation is blown in.

You’ve also got heat-producing devices up there. Recessed lights. Furnace and stove flues. Your chimney. If you are using cellulose insulation, you’ll need to construct barriers around the devices. With fiberglass, your local home-center sells shields and covers.

Regarding your recessed lights: They may, in fact, be rated Type-IC. If, however, they are not, remember this: you need to build a dry-wall box around the fixture to keep the insulation away from it and to prevent a fire hazard. Fill in the seams with spray foam.

Remember this, too: insulation falling through the attic access into your living space is not a good thing for the family, your pets or for guests. The hatch “door” needs oversized padding (insulation, pillow, foam) extending beyond its edges. And the edges need a small wall built around them to prevent insulation falling through when the access is open.

And while you’re up there …

You also need to be on the lookout for actual or potential roof leaks and here’s why: wet blown-in attic cellulose takes forever to dry out and, most times, never does. If you end up with saturated cellulose in your attic, the anti-mold additives don’t work and your cellulose gets moldy. And envision this: hiring post-installation contractors having to haul the ruined cellulose back downstairs, and outside – by hand – to clean up the mess.

Prevention is better than remediation.

Eaves and soffits. You finally get to use those words!

Gabble roof with attic windows.

Repeat three times: Don’t block the airflow through your soffits. (OK, take a minute to look up the definition of a soffit.)

The fact is, blown-in insulation can block airflow through your eaves. You don’t want this to happen as it traps and builds up hot air. And hot air (in the non-political sense) can create wood rot and mold. This is not a good thing.

You can prevent it from happening. How? Install ventilation baffles (essentially plastic or foam vents) into the eaves by pulling the existing insulation away from the roof, positioning the new vent chute so the bottom extends six inches into the overhang and stapling it into place.

The eaves don’t get blocked. Hot air doesn’t get formed. And you avoid wood rot and mold.

And that’s a good thing.

Picking the person with the truck. You know, the insulation contractor.

Yes, in your mind (and even in our approach to this article), we characterized this as a DIY job. Your ego may require that you think of this as your job, but the fact is: your role largely is confined to preparation. Unless you are in this line of work, let’s agree to agree: You need a professional for the actual installation. (Chances are, your wife and/or your neighbor are telling you the same thing. Listen to them!)

Here’s what you need to do: Identify an insulation contractor who knows what he or she is doing. That’s probably not the guy who cuts your lawn and says he can do it for you in the evenings and on Sundays.

A better approach:

  • If you are going the cellulose route, go to the Cellulose Insulation Manufacturers Association’s (CIMAwebsite and find a real professional who’s been there and done that.
  • Similarly, NAIMA (the North American Insulation Manufacturers Association) has a website that provides you with information about fiberglass and wool insulation products.

Capability and experience is one thing. As is insurance and a contractor license. And references you can actually call. Discuss costs and get three written estimates, but only after you first determine what he or she will do and what you’ll do when you slip into those new coveralls you just purchased. Also discuss: coverage area, thickness needed, R-value desired/required.

Insulation Contractor Talk for Dummies.

Attic with dormer and insulation.

Your greatest concern, of course, is that you don’t have a clue how to talk with the contractor or even to evaluate what he or she says.

To help you, here are some points from the ICTfD handbook.

  • Recommended ceiling insulation level for most attics: R-38. This would require insulation extending 12 to 15 inches from the drywall. For colder regions: R-49 probably needs.
  • Openings that aren’t sealed can cause a home to lose 30% or more of its conditioned air.
  • So what is cellulose and rock wool, anyway?
    • Cellulose is made from recycled newspaper, cardboard, and other wood-based materials. Treated with boric acid and other substances, it is flame resistant, mold-resistant and less expensive than blown-in or fiberglass batts. And it has a higher R-rating. And during installation, you are going to find it friendlier to your skin and lungs.
    • Rock wool, meanwhile, comes from the slag that forms on the surface of molten metal. Essentially, it is recycled rock, making it moisture-proof as well as non-flammable. It’s heavier than fiberglass and it insulates better.
  • A bag of cellulose insulation covers about 30-35 square feet of attic space if you are blowing in 10 inches. A bag of fiberglass insulation will cover approximately 65 square feet.

Moving Forward.

Net-net, for many reasons, you’re probably going to decide this job is well worth doing. It’s also worth doing the right way. And that means preparation and common sense. Enjoy.

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