DIY Guide To Blown-In Attic Insulation

ATTIC INSULATION MATERIAL OPTIONS

There are many choices available for you when it comes to attic insulation. Let’s take a quick look at the most popular ones, and discuss the pros and cons of each type.

SPRAY FOAM INSULATION – If you have the money to pay for spray foam in your attic, then you may want to stop reading now and go get that done.  For most of us, installing spray foam insulation in their attic is just not a DIY project, and it is too costly for your average homeowner.  Does it work?  Yeah, spray foam is great. So if you can write a check for it, just stop reading and go pick up the phone.  Turn your attic into a big Yeti Cooler.

With spray foam, you also get the benefit of moving the home’s conditioned envelope from the living space up to the attic just under the roof decking.  This will help a lot if your HVAC equipment is located in the attic (which, by the way, is the dumbest place to put your HVAC equipment).  Your equipment and duct runs will no longer be exposed to extreme hot and cold temperatures once that envelope gets extended.  The only caveat I can think of when it comes to spray foam insulation is that you do run the risk of trapping moisture around the roof deck if you develop a leak in your roof.  If you are OK with this risk, then foam is a great choice for attic insulation…even though it can be double to triple the cost of other options.

FIBERGLASS BATTS – Fiberglass batt insulation is woven rolls of fiberglass that are quick and easy to install.  You cut it open and roll it out.  The problem with fiberglass batts installed in the attic is that they are prone to gaps between the pieces and you don’t get complete coverage.  This leaves you with areas of your ceiling that have no insulation on them.  You can see an example of these gaps in the thermal image I took below.  For this reason, I have to give fiberglass batts a big ol’ thumbs down.  There are much better options for you to use. Skip this stuff altogether.

BLOWN IN FIBERGLASS – Blown-in fiberglass insulation is found in about 75% of the houses I see.  This is small pieces of fiberglass that come in a bag and are installed with blower machine.  The blown-in fiberglass works much better than the fiberglass batts, as you don’t have gaps in the coverage.  It’s not a horrible choice, but I like cellulose a bit better for a few reasons.  1. It does a better job at restricting airflow when you have a lot of it.  While neither material is listed as a true air barrier (meaning it blocks airflow completely), cellulose will do a better job at stopping air transfer between the living space below and the attic when you blow in a thick blanket of it. 2. Cellulose doesn’t make me itch.  I know that shouldn’t be a real reason, but if you crawled through as much of this crap as I do, you wouldn’t like it either.

BLOWN-IN CELLULOSE – Cellulose is becoming more and more popular in new houses I inspect, and it is the material I chose to use in my home.  The R-value is about the same as blown fiberglass (not enough of a difference to speak of). The cost is also comparable to blown fiberglass.  As I mentioned above, I like cellulose because I don’t itch when around it, and it does a better job at air sealing than fiberglass.  So for those two reasons, I decided to go with blown-in cellulose.

Note: It will not hurt anything to mix the two different materials.  Don’t worry about blowing in a new layer of cellulose insulation over old fiberglass. 

PREPPING YOUR ATTIC FOR NEW INSULATION

Much like a quality paint job, the prep work is vital to a quality end product when it comes to insulating your attic. Let’s look at each step and I’ll explain what you need to do and why, in order to make your new insulation perform as well as it can.

I had about 50 hours of prep work in my attic before I even ordered my insulation from Lowe’s.  While your time will vary, you need to put forth the effort if you want to reap the full benefits of your new attic insulation.  Does it suck spending so much time to get things ready?  Yep, sure does.  You know what else sucks?  Spending all that extra money every month on heating and cooling, and not being comfortable in your home. That sucks even more in my book.

Let’s look at the prep work that I needed to do in my home.  Most of this will apply to you, so be sure you do not skip these steps if you want the best possible results with your new attic insulation. 

BUILD A CATWALK ACROSS YOUR ATTIC

If you are OCD like me and don’t want to block off your attic for future…whatever, you need a way to traverse it without disturbing the new blanket of love that is two feet of cellulose insulation.  I’m lucky in the fact that my attic is tall enough to walk around in.  I freely admit that makes things easier to deal with.   My plan was simple. Build an elevated floor so that I could walk from one end of the attic to the other and not touch my new insulation.  How you go about this in your house will depend on a lot of factors that I can’t see from here.  But what I will tell you is to make it strong, and tall enough to get the desired depth of your insulation.  For me, this was about 16″ tall to the top of the walkway. I recorded a short video below to show you how I built the risers for my catwalk.  These worked well, so feel free to copy this simple design.

AIR SEAL YOUR ATTIC FLOOR/CEILING PLANE

This is the most important step in the prep work. Don’t get lazy here. Because cellulose and fiberglass insulation are both classified as ‘air permeable‘ (meaning that they don’t stop airflow), you must fill all the holes that lead down into living space before you pile a few feet of insulation on top of it.  If you don’t take the time to seal things as much as possible, you’ll get hot/cold air leaking down into your interior walls, no matter how many inches of insulation you have.  Remember that heat transfer happens in 3 ways (conduction/convection/radiation) and we need to address all of them.  Take a look at the example thermal image below of my living room and you will see the orange and yellow ghosting lines leading down the wall.  This was taken on a 90-degree day in early September.  The warmest parts are at the point where the top of the wall and ceiling meet.  That is because the hot air from the attic is being drawn down behind the drywall into the wall cavity.  You can see the wall gets cooler the lower you go.  That is because the temperature difference is leveling out due to the hot air from the attic moving down into the colder wall.  Thermodynamics 101. 

The goal here is to hunt down all the cracks and holes that allow air to move between the attic space and living space, and seal them up.  This would be really easy without any insulation in the way, but in the real world, we must dig through what is already there and seal the holes up. This process is not ‘hard’, but it is not fun either.  You need to track down your walls in the attic and dig through the existing insulation to find the exposed 2×4/drywall intersection.  This is the point you want to fill with spray foam or caulk.  Either will work fine.  Keep in mind this process needs to be done ALL OVER THE ATTIC.  Not just in one spot.   I will freely admit this is the worse part of the job.  But it is crucial if you want things done correctly.

I had a couple of spots where closet walls met together where I could see down in behind the drywall from the attic.  I find these areas pretty often in other houses during my home inspections so you may have them as well.  A rough-cut piece of drywall, plywood, or thick XPS foam will seal things off nicely.  Simply rough cut to cover the bulk of the hole, and foam in place to air seal around the edges.  Just remember to support things as needed. The bigger the hole to cover, the stronger the material needs to be.  You will be piling on a few feet of insulation after all this done.  If you don’t build it strong enough, it may cave in from the weight of the insulation.

AIR SEAL RECESSED LIGHTS

Most homes have at least a couple of recessed lights in the ceiling (aka “can lights”).  Some homes have a lot of them.  In the geeky-home energy world, we call recessed lights ‘6″ Chimneys’ because of the amount of air that leaks through them.  If you have a lot of recessed lights, they are a big source of your conditioned air escaping the living space and making it up into the attic.  There are two types of recessed lights you can have.  IC and Non-IC Rated.  IC stands for Insulation Contact.  Most newer homes have IC Rated lights if the builder wasn’t a total cheapskate.  This means you can pile insulation on them without worry of causing a fire.  If your lights are the cheaper Non-IC variety, you are not supposed to allow insulation to touch the housing.   Both styles still need to be air sealed however, and that is easily done with a special cover like the ones seen below.  These are made to resist fire and air seal the lights all at the same time.  You simply set them over the light fixture and foam them in place. Tenmat Recessed Light Covers.

Non-IC rated recessed lights are not supposed to be buried with insulation.  You can normally tell you have Non-IC housings by all the holes in them.  Some are also labeled with a warning that tells you not to let insulation touch this housing.   The idea is they could get hot enough to ignite something in the attic and start a fire.  While that may have been true in the past with incandescent light bulbs, modern LED bulbs run at a fraction of the temperature of old bulbs. (You are running LED bulbs, aren’t you?)

Even though the LED lights themselves run cool, the power supply of modern LED puck lights do give off a bit of heat, though I seriously doubt it is enough to cause something to burn. Installing LED lights all but eliminates the chance of something crazy like a fire happening from the heat of a light bulb in your recessed lights.

To test my theory I took one of my lights out of the ceiling and installed it on an old drop light.  I left it on for 1 hour to let it get as hot as possible, and the temperature maxed out at 114 degrees.  That is a far cry from a temperature that would ignite anything.  I’m sure other brands of lights will vary in temperature, but I can’t imagine a scenario where they could get hot enough to cause a problem.  Note: My very unscientific test was performed in the open air where things could cool.  Once you install these lights in the housing, there is likely no airflow.  That will cause everything to heat up more.  Will it be enough to cause a fire?  I highly doubt it, though I suppose the risk is always there.

If you install the proper air seal covers and use a high-quality LED puck light, the chance of something bad happening is extremely low.

INSTALL BAFFLES ON YOUR ROOF STRUCTURE

Most homes have vented attics.  This means there are holes in your soffits (the area of the roof around your gutters), and holes around the peak of the roof.  These two holes create a path for cool air to come in the intake (lower vent) and wash the bottom of your roof sheathing with fresh air, exiting out the upper vent.  This convective loop of airflow helps remove moisture and keep the attic cool-ish (we all know there is no such thing as a cool attic in August).  The baffles are installed to hold back the insulation so this venting can still happen.  If you don’t create a dam for the insulation to pile up against you’ll block off the path that the fresh airflow needs to travel.  Doing so can cause lots of moisture build-up in the attic which leads to condensation, which leads to rot, and mold, and World War 3.  Below is an awesome diagram I saw on Fine Homebuilding that should help you understand what a baffle does. 

There are many options available for baffles, but I decided to make my own out of 1/2″ foam board.  I bought 12 pieces and cut them in half longways, so my $10.00 piece of foam board would net me 16 linear feet of baffle 24″ tall.  Perfect.   You can buy plastic attic baffles but they can get pricey as you must install them in every rafter bay.  Avoid the thin Styrofoam versions if you can; they are cheap and tear really easy.  My best advice I can give you is to do whatever you need to do in order to create this dam and keep your venting open as much as possible.  I could write another whole article on attic venting, so I won’t dive too deep into it right now.  Just don’t block off your vents with your new insulation.

ATTIC KNEE WALL INSULATION

Here is one area you may or may not have in your attic (depending on how your home is laid out).  A knee wall is a small wall that sticks up in the attic.  These are found in rooms with vaulted ceilings or weird angles like stairwells.  The best way to think about this is that if you see vertical drywall in your attic, you will need to follow this step before you blow in your new insulation.  Most homes have fiberglass batt insulation on these walls from the builder and we have already established that they suck and have to go.  Just like on your ceiling, they don’t have uniform coverage, and lots of times they fall back off the drywall from being poorly installed or from gravity.  Once you get a gap between the face of the insulation and the back of the drywall you lose any R-value that wall had.  The thermal imagine below shows the small wall from my attic before I touched it.  The fiberglass batts that were installed by the builder had started to fall back off the drywall and you can see the heat from the attic radiating through the wall. The orange/yellow rectangles are the exposed section of wall sticking up in the attic.

I pulled all the fiberglass batts off my wall and installed poor man’s spray foam, also known as the cut and cobble method.  This is when you use sheets of rigid foam board and cut them into strips that loosely fit between the 2×4 wall studs.  I shoot for a total width minus a 1/2″.  This gives me 1/4″ on each side of the stud to fill with spray foam, which ensures 100% coverage of the drywall stud bay.  I ended up gluing 3 layers of 2″ board, for a total of 6″ of closed cell foam–about an R-30.

Pro-tip: When you are gluing layers of foam board together, be sure and use a glue that is water-based.  I used this stuff and it worked great: Powergrab  If you use something that is not water based, it will eat away at the foam and the layers won’t stick together.

Option #2 – Some homes have a lot of knee walls to contend with.  If you are in that boat it may be cheaper and easier to hire a spray foam company to come in and shoot the walls with open-cell foam.  You’ll need to run the numbers and see what is best for you, just make sure you don’t skip this step altogether.

EXTEND YOUR B-VENT (AS NEEDED)

Your B-Vent is a double wall flue pipe that HVAC (furnace/boiler) systems and water heaters use to vent their flue gases out into the atmosphere.  These normally run up the center of the house, and stick out of the roof.   The rule is that all combustible materials (anything that can burn) must remain 1″ from this vent stack.  My B-Vent made a beeline for the back of the roof in the form of a hard angle as soon as it came through the drywall.  In order for me to follow the rules and keep that 1″ clearance, I needed to extend the vent straight up from the ceiling about two feet, then make the angle over to the roofline.  This will allow me to blow my 20″ of insulation and not touch the horizontal run.

You may need to do this too, depending on how your B-Vent has been run (if you have one at all).  If you are lucky enough for the pipe to run straight up from the ceiling to the roof, then you can skip this step.  For the rest of you: make sure it’s done.

Note 1.0- This is a job you may want to leave to a pro.  If you don’t get it 100% correct, you could have a flue pipe come apart in the attic, and that would be very bad.  Like create a CO danger and make you sick or kill you bad.  Know the limits of your abilities and knowledge.

Note 2.0- If your home only has electric utilities, you will not have any vents to worry about.  You can skip this step and the next one too. 

HEAT SHIELD FOR B-VENT FLUE PIPES

Now that we have our B-Vent extended up away from everything, let’s get our heat shield installed to keep out new insulation from touching the pipe.  The rule is that you must keep combustibles off of the B-Vent pipe at least 1″.   Part of me thinks this is a waste of time, but I did go ahead and build a heat shield for mine because I’m OCD, and want to set a good example for you.

However, the side of me that likes to argue decided to see how hot I could make my B-Vent in the attic.  Could I set something on fire if I wanted to?  I wanted to see the worst case scenario and get the pipe as hot as I could.  Let me be perfectly clear: I am telling you to follow my lead and install the proper heat shield around your B-Vent. But if you are curious about the science, here you go…

For my house, it was a total waste of time.  I cranked up my water heater and let it run for 60 minutes to try and make the B-Vent as hot as possible.  Even so, I could only get it to about 72 degrees Fahrenheit in the attic.  That is a long way from being hot enough to set anything on fire.  B-Vents have an extra air chamber and outer wall to help buffer the temperature down (in what is known as a double-wall pipe),  and I can’t see a scenario where something could ever get hot enough to be a problem.

Things to remember: My home ONLY has a water heater venting into the B-Vent now because I recently replaced my old furnace with a new high-efficiency unit. It has a PVC vent that runs out of the side of the house, so now my original 5″ B-Vent only has a single water heater venting into it.  This is technically known as an orphaned water heater.  Your house may still have a furnace and water heater using the B-Vent, so do not take my house as the norm.  It’s just an example.

Again, I’m telling you to install the proper heat shield around your B-Vent because it’s the correct thing to do.  

And, because it’s really easy to do.  I picked up a short section of 8″ ductwork and cut tabs out of the base of the duct and bent every other one in and out.  This gave me a stable foot to set the section of ductwork on in the attic.  Ductwork comes in a circle shape but has to be snapped together along a seam.  This will let you wrap it around your B-Vent without having to disconnect the B-Vent.  Once everything was set where I wanted it, I foamed the base of the heat shield to the drywall ceiling.  This locked it in place and will keep the insulation a safe distance from the B-Vent.

HOW TO INSTALL BLOWN-IN ATTIC INSULATION

You’ve worked your tail off getting things ready for the new insulation and now it’s time to install that new blanket of love.

The delivery of my materials arrived at about 9 am on a cloudy, rainy Saturday morning.  The online calculator from Lowe’s website said that I needed 138 bags of cellulose insulation to reach my desired depth of 20″.  That seemed a bit excessive to me, so I rolled the dice and ordered 125.  The truck pulled up and dropped off the blower machine, and four pallets of insulation.  Below are my tips for install day.  It’s all downhill from here…Kinda.

GET THE MATERIALS DELIVERED – Unless you own a U-Haul truck, just pay the money to have all your materials delivered.  It will save you half a day in time, and you won’t be exhausted from hauling all that material from the store to your house.  Save your energy…you’ll need it.

RALLY THE TROOPS – Here is where you’ll need a little help from your friends.  Up until now, this has been a one-man job for me, but you can’t feed the machine down below and handle the line in the attic at the same time.  I strongly recommend that you get at least one (preferably two) friends to help.  Especially if you have to pack the insulation a long way from your driveway.  The first five bags won’t be too heavy, but bag 95 will weigh a ton.   My attic access is about 10 ft from my garage door, which made things really easy to stage next to the blower machine.

I’m extremely fortunate to have a badass wife (Michelle) who is ready for whatever I throw at her.  I know what you must be thinking, “but Ben, isn’t living with you all home improvement and rainbows?”  For the most part, you’d be right, but you can’t make an omelet without cracking a few eggs.  So for that, I salute you, Michelle.

GRAB A ROLL OF TAPE AND PIECE OF PVC – Your machine (if it was like mine) will come with a trash can full of beat up hose that may be in a couple of sections.  My hose was 2″ (I’d bet that is standard for these smaller machines).  Nothing will slow you down more than having to deal with these hose sections coming apart during the job, so be sure and grab a small piece of 2″ PVC with your materials list (a 2ft piece should be perfect).  I just happen to have some conduit laying around and cut about a 10″ piece to use as a connector.  Slip the PVC in one end of a hose section and wrap it in tape.  Then slip the other end of a section in and tape the two together.  This will create a solid connection for the pieces of hose so that will not come loose during the installation of your insulation.  I went ahead and donated my connector to the trash can of hose back to Lowe’s so the next guy wouldn’t have to scramble.  You’re welcome, fellow DIYer.

BE PREPARED FOR A BIG MESS – Once you start blowing the insulation, things are going to get messy.  The bricks of material are packed densely into their bags, and you must break them apart into smaller chunks to feed the machine.  You are going to have small pieces fall around the machine.  If your access point to the attic is not in the garage, I highly recommend you place a large sheet or drop cloth down to help contain things.  If your access is in your closet, you’ll want to clean it out or cover everything in sheets.  The blower machine kicks up a lot of dust from breaking up the chunks with its agitator.  Once the party starts you will not have time to stop and pick things up.  The machine will run through the material just about as fast as you can feed it.

Note: This is a very dusty job.  Do yourself a favor and wear a high-quality mask.  I wore an N95 disposable mask but actually went through 3 of them.  They got really nasty after a couple of hours so I tossed them out and grabbed another. N95 Mask

MAKE SURE YOU GET TO EVERY CORNER OF YOUR ATTIC- This should go without saying, but make sure you can reach all of the attic.  The machine does a good job of throwing the material about 10ft, but you need to make sure you will reach all of the corners.  I recorded a short video as an example of what to expect from the Cocoon cellulose machine from Lowe’s.  As you can see it’s not blasting out of the hose, so expect to be there a while.  The process is a bit slow going.

TOTAL COST FOR BLOWN-IN INSULATION

Here is the breakdown for the total cost of the project.

We started around 9am the morning the materials were delivered, and I climbed down from the attic at about 1:30pm, only stopping to grab some water or change my dust mask.  Clearly, your time will vary, but I would think just about any home could be finished in a day.  As long as you’ve got everything prepped, and enough material to do the job, once you start the machine it is all downhill from there.  Let’s look at the total cost of the job for my house.  Remember: I added about 14-16″ of blown-in cellulose, installed a baffle system all around the perimeter of the attic with foam board, extended my B-Vent for the gas appliance, insulated my knee walls with 6″ of rigid foam board and air sealed my ceiling plane with fire-rated can foam.

1. 125 bricks of cellulose.  The cost per brick is about $10.00.  However, Lowe’s has bulk pricing on this when you buy more than 100 bricks.  That brought my total to $7.00 per brick.  I ended up returning 18, so my total cost on the cellulose insulation itself was about $750.00.
2. The 1/2 foam board used to make my baffles (or insulation dams) was $10.00 a sheet.  I used 12 sheets for a total of $120.00
3. The wood for the catwalk I had left over from another project, so I consider that old money and a freebie.  If you had to buy this stuff I’d budget about $200.00
4. I used two full sheets of 2″ rigid foam to insulate the walls.  It’s $27.00 a sheet for a total of $54.00
5. I ended up using about 5 cans of the Great Stuff Pro Foam.  This is about $12.00 a can.  You could save a bunch here by using caulk to do most of your air sealing, but the foam is so much faster it was worth the extra cost.  Spray Foam – $60.00
6. A couple of new short sections and an elbow of B-Vent for my flue pipe. $100.00

This brings my total to around $1300.00 in materials.

Not bad for a job that would likely cost around $3-5k if you hired a pro.  I called 3 local insulation contractors in Louisville and tried to gauge what it would cost to have this done, air sealing and all, and none of them would even give me a price.  All said it was a “waste of time” to do all the extra prep work I was asking for.  This tells me that the “pros” don’t want to spend the time to do things correctly.  They can make more money by just blowing in a new layer of insulation and running off to the next gig.  If you decide that this job is more than you want to tackle, be sure and gauge your contractor by the prep work in this guide.  If they are not willing to do things correctly, I’d advise you to move on and find a new insulation contractor.

Now, through the magic of video editing, you can watch my 5-hour job in 3 minutes.  Thanks for reading, and if I can help in any way please give me a shout! Stay warm!