A poorly insulated attic is easily one of the top 3 things I find in just about every home where I perform a home inspection in Louisville, KY. I’d be willing to bet it’s like that in lots of other areas of the country as well. So I decided that when I finally got around to fixing my own home’s insulation in the attic, I would write a DIY guide for it. A properly insulated attic is one of the easiest and highest ROI (return on investment) things you can do to your home. Most folks can recoup their cost in as little as a year or two. So the faster you muster up the get-up-and-go to get this knocked out, the better off you’ll be.
This DIY guide explains step-by-step how to insulate your attic properly. We’ll cover the different types of insulation you can use, the prep work you need to do before adding the insulation, and everything in between. As with all things concerning a home, no guide or list can be all-inclusive, so this should be read with the understanding that you may not be able to follow it verbatim, but it should cover the topic for the vast majority of you. As always, feel free to give me a shout if you are unsure or have questions about your process. I’m here to help. You can tweet me @inspectorben, or You can email me here.
UPDATE: Below is a list of frequently asked questions about insulating your attic. You’ll want to read the whole process to fully understand how to insulate your attic space properly, but this FAQ will get you started.
If you are curious about the energy savings, here is a copy of my utility bills a year later after finishing my attic. I cut my usage for the month nearly in half. If this doesn’t motivate you to get your home fixed, what will?!?
Can you install cellulose insulation over old fiberglass insulation?
Yes. It will not cause any problems to mix the two types. The most important step is to air seal your attic before you install the new insulation.
Does cellulose insulation create an air barrier?
Once cellulose insulation reaches a certain depth in the attic, it can act as an effective are barrier and slow down the movement of air between the living space and the attic.
Is rolled insulation better than blown-in insulation?
No. Rolled batt insulation creates gaps in your coverage after it has been installed. Blown-in insulation is a much better choice for attics as the small pieces will fill those small areas.
What is the best type of insulation to use in my attic?
While every application has its own challenges, cellulose insulation is one of the most common found in modern construction due to its R-Value per inch and air sealing capabilities at higher depths.
Can you have too much insulation in your attic?
No. In general, the deeper the insulation levels the better off you will be. However, you must make sure you are not blocking off your attic ventilation for moisture removal.
Insulation Material Options – Why blown In Insulation is the best option
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.
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.
Installation Time – Rally the Troops
So 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 9am 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.
Grand Total in Cost
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.
- 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.
- 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
- 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
- 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
- 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
- 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!
Hi, I’m Ben, and I inspect houses. I grew up with a hammer in my hand, and have been a professional home inspector for 12 years. My blog is here for info about home inspections around the Louisville, Kentucky area, and just about anything construction-related.
I have super tuff 1″ available to do what you did. Is this product acceptable for fire codes in an attic ? There is no storage no furnace or water heater vent pipe or can lights.
I’m not sure I understand your question, James. Any foam product that is fire rated will say so on the package- I’d imagine. If you are unsure about a specific product I’d call the manufacturer and see if they can tell you what you are looking for.
Great write up! Thank you! I’m planning a similar approach in Oregon. question…how did you air seal the exterior top plate and how did you get the rigid foam sheet baffles to connect to the top plate?
I’m considering using 1/2 rigid foam for the baffles and cutting 22.5 x 4 inch pieces to fill the gap between the top plate the rigid baffle with spray foam to lock it all in.
Thanks in advance!!
The top plate around the perimeter of the attic is a tough spot to reach. Some areas will simply go unsealed. Just do your best to get as many as possible. I used mostly canned foam (Great Stuff) and painters caulk to do all my air sealing. Your plan sounds like a good one. Just make sure you don’t block off your ventilation and you’ll be golden.
I did not do a catwalk prior to blowing in the cellulose and now wish I did. Can I lay one out on top of the cellulose?
You certainly can, but I would not recommend it. What will likely end up happening is the catwalk will feel like walking on a waterbed (if you are old enough to remember those things). If you lose your balance it may cause you to fall, and that would end very badly. At this point, I would recommend digging through your insulation and building a proper catwalk, and then ‘repair’ the holes that you made to do so.
Great video! I learned a lot and believe that “If you’re going to do a job, do it Right!”
Discovered several problems in my attic: 1) new flexible HVAC ductwork leaking (missing wire ties, gaps on fiberboard plenums, kinks, no support for long runs, etc etc) AND vinyl soffit vents Without holes!!!
I’ve sealed all HVAC collar leaks with mastic DP 1030 and new correct wire ties (2 per collar) and shortened + reroute + support all flexible R6.2 ducts. This took me 3 months…I’m senior citizen…roof is 4/12 pitch. House 60 yrs old and renovated by “reputable” contractor. BS.
Now vacuuming via Dry Vac all loose fiberglass insulation on soffits and making my own Soffit vents with 1/5″ underlayment plywood.
Have appointment with roofing company to estimate cost of removing soffit vents + cutting holes.
I hate half assed work!
If too much $$ I’ll do it myself!
Good for you Martin! Taking the time to do things correctly will pay off in the end. I’ve all but forgotten how much it sucked to prep my attic when I did it, but being able to turn down the A/C and make my home as cool as I want it to be is priceless at this point.
Thanks for the great info! I have a major list of corrections in my attic I’m trying to prep for, including fixing the horrible ducting job that was done. Metal main supply trunk and flex distribution boxes are bare, un-insulated metal in an attic, flex duct is only R4.2, lazily ran with bends and sags. I plan to redo that whole system with my own-made insulated distribution boxes, R8 ducting (stretched tight), hard elbows for turns. Plus route the bath fans through vents (instead of the hose being aimed at a soffit vent), air seal the wall tops, add more soffit and roof vents (esp to accommodate 2 new whole house fans), run cabling for security cameras, add an attic TV antenna, and then blow in R49 worth of cellulose. On that, question for you. I was originally going to suck out the current blown fiberglass to make it easier to work up there, esp with the duct work, soffit work, and air sealing. But I see you left yours in place. Is it easier to suck it all out or just leave it and work with it in place?
Hey Frank! If I had all that to do first, I’d pay someone to come out and remove it. Then I’d fix all my stuff and blow my new insulation in myself.
Yeah kinda my thought though the company I contacted recently isn’t doing any insulation work right now. Probably because of COVID. Thought about renting the machine and vacuuming myself. But that can get messy!
Thanks for the great info! Just bought our house and it seems our house is colder than I would like. So I’m looking to do this with the attic however I might have to do quite a bit more prep work. Found cracked drywall near HVAC flue with a 5×3 hole that seems to have never been closed, and a squirrel in the attic. (Neighbor said roof was rotted at one point and had lots of birds in the there before they finished the roof and they did not do a thorough job) There seems to be newly blown insulation on top of old insulation. I haven’t gone up there to check yet but what are your suggestions. Because there were/are animals up there (once they are removed) should I remove old insulation to prevent new inhabitants and fog/decontaminate the place prior to fixing the drywall and following your steps? Or fog the place with the current insulation then fill the holes?
I’m not sure I’m am following you 100%. What did your home inspector say about the condition of the attic before you bought it? Any insulation that is suspect of contamination by animals should be removed for your health and safety. Also, just a side note, depending on how old the house is, you may have old Vermiculite insulation. If that is the case be sure you have a pro perform the proper mitigation. You can research that to learn more about the risk associated with that material.
Hey Ben,
I’ve read lots of information about air sealing and insulating an attic and yours is the best. Seriously.
There’s the description from start to finish, 23 photos, 6 thermal images, 3 videos and 1 diagram. It’s not a guide it’s a documentary.
I’ve decided to air seal and insulate my attic, but there is no way my wife will load the blower. I not even going to ask her.
You must have spent weeks putting together the guide.
Thank you so much .
Thanks, Mike! It’s was a labor of love for sure. I just ask that folks share the love to help others. It’s not fun money to spend on your home, but boy is it nice to be comfortable and have low energy bills. If you need any help with your place to give me a shout! Thanks for reading.
Hello, Great info provided in this article. Had two quick question, I noticed the call out about doming all recessed lights and spray foaming around the dome. would you do the same for ceiling outlet boxes used for fans/ flush mount lights etc?
Also how would address ceiling around a bathroom exhaust fan prior to blowing insulation in?
Thanks in advance
Jon
Hey Jon- It’s a good idea to make sure you seal up all the openings in the ceiling plane that you can. Using the expensive covers for your junction boxes are not necessary. You can foam around the edge of the box (you can always use caulk if the cut of the drywall is nice and clean), and just a dab of foam where the wire enters the back of the junction box, and that will seal off any airflow that may come through. You can read this old post I wrote about air sealing your electrical boxes. https://abihomeservices.com/save-money-air-seal-your-house/
Thanks for all of the info! Was thinking about just building a cat walk directly on the trusses and then blowing insulation on top of that. I was planning on making a 3 foot wide cat walk. I don’t want to spend too much time building an elevated cat walk. What do you think? Also, how much did all of this lower your energy bills?
Thanks!
You’ll thank yourself later for that nice catwalk. Spend the time upfront and you’ll be glad you did.
As far as money saved on monthly bills I lowered mine about 30-40%. My house was really bad to start, so I can’t say that you will experience the same savings- but it will help. Good for you getting this done, and please feel free to reach out to me if you have any questions.
Would you still cover your recessed lighting even if you have IC rated cans?
I would- just so you can get them out later on if you need to. If the day ever came you needed to remove the housing, it would be a nightmare digging through all that foam.