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Save Mucho Money by Reinsulating Your Home’s Exterior Walls

Clever Dude and the insulation blower machine

Our home was built in 1941, long before insulation was commonly used, much less a standard in new home construction. We bought the home in 2004, but didn’t know this fact until we really started questioning why the walls were so cold, and the house so drafty in the winter. Bear in mind, however, that the last owners built additions when insulation was standard, and those walls definitely were insulated. The main question was whether the original parts of the house were insulated.

Recall that we have already insulated our crawl space ourselves, and added some extra exterior wall insulation already.

We weren’t quite sure whether the walls were insulated or not until we did some recent home repair and renovation. The first hint was when we installed a new power outlet, and my father-in-law (FIL) found no insulation in that cavity. But we didn’t truly know whether that was indicative of the whole house or just that section until my brother-in-law (BIL) visited last spring.

The last owners replaced the old asbestos siding with vinyl siding, and in the process added a layer of Styrofoam insulation under the new siding (it’s the green stuff you’ll see in later photos). Luckily, my BIL has an insulation side-business and was nice enough to do some complimentary work for me. He popped up a row of siding, drilled a hole halfway up the wall and confirmed there was absolutely no other insulation. I was actually happy about this finding as it’s easier to add insulation when it’s absent rather than when there’s already some present.

How we insulated our exterior walls

I’m going to preface this section with “Your results may vary” because each home is different, your equipment will be different and you probably won’t have a generous relative who knows how to do it already.

Common Materials (aka “What we used for our home”)

For our home, the minimum equipment we needed was:

  • Siding Removal Tool – a necessity to pop off and, more importantly, pop back on the siding. It’s only $5 at Amazon
  • Insulation Blower – Although my BIL has a heavy-duty $20,000 insulation blower, it was too inconvenient to transport the giant 4 hours from PA to MD, so we rented one from Rentals Unlimited. We paid about $60 for the day. You can also get them from Home Depot and other equipment rental places, but they may be in short supply. It’s small, but still heavy. Take another strong gent with you to pick it up and unload it.
  • Cellulose Insulation (NOT fiberglass)- From the website: “Cellulose Insulation is one of the greenest products in the world. Cellulose insulation is made from recycled newsprint and other paper sources, paper that might otherwise end up in landfills”. We bought the Green Fiber brand, which costs about $10 per pack at Home Depot. For our job, we used 12 packs before we had to return the rented blower machine.
    For walls, we used the R-19 calculation on the back of the package, or also found here. We were originally going to do 700 sq ft of wall space, but only got through about 400 sq ft when the 8 hours ran out. Also, I decided against doing the second floor for other reasons. We got through 2 side walls and half the front (the back walls are additions that are already insulated).
  • Hose nozzle and hose clamps – The machine came with a very long hose, but didn’t have the proper nozzle on the end to ensure the size of the insulation going in wasn’t too large, and to be able to control the flow better. My BIL had the proper fitting (which accidentally fell into the 2nd wall we did and is now insulating our house, so be careful). Just make sure you get all the proper attachments with your machine.The rental was also missing hose clamps to keep the hose secured to both the machine and the nozzle. My BIL had one hose clamp, but we had to use duct tape for the rest.
  • Power Corded Drill -You can try to use a battery-powered drill, but if you’re doing a lot of wall space, you want a corded drill, and a decent one at that. It’s also helpful if the drill has a side-handle so you can grip it with both hands. When you drill into the wall, you need to be careful not to let the drill go in too far and hit the other side (wasn’t a problem for us as the drill bit wasn’t long enough to do that).
  • Self Feed Drill Bit – While some people use a drill bit that leaves you with a nice little wooden circle that you can reuse to fill the hole you made, we used self feed drill bit to just make a hole, then plugged it with a plastic plug. The size of the drill depends on the size of the plug you buy, or vice-versa, so shop around…
  • Sidewall Insulation Plugs – This is a more specialized item, and the link I provide here is just one search result. I’m not sure where my BIL bought his back, or the size (they looked like 2″ plugs), but I know he paid about $60 for the whole bag. As mentioned, these will need to be the same size as the holes you drill.
  • Miscellaneous things like a pole (like a broom handle) to stir/break apart the cellulose blocks in the machine’s hopper, or a can to break it up into another container before putting it into the hopper. You’ll need a face mask since you’re working around dusty insulation (you’ll understand when you start working with it). Also, a stud-finder might help, but we utilized the existing nails and our own knowledge that studs are generally 16″ apart to determine where to drill (with only 2-3 mistakes).

Clever Dude’s BIL pumping insulation into the walls

Tips for Insulating your Exterior Walls

Again, this all depends on your home and what tools/equipment to which you have access, but we learned a few things from this experience:

  1. Identify where all the outlets and switches are before drilling! You DO NOT want to accidentally drill into a live wire or a socket!
  2. If at all possible, insulate from the outside of the home. If you don’t have vinyl siding, most likely it’s easier to patch your interior drywall/plaster than your existing siding (or brick), but it’s a dusty, messy job, so if you can do all the work from the outside, then do it.
  3. Drill a top and a bottom hole for each cavity. You need an escape vent for the air you’re pumping into the wall. If not, your hose will get backed up from all the pressure pushing back and you’ll get really frustrated like this guy.
  4. You need to pump insulation in both the top and bottom of the cavity. If you only pump in the top, then it won’t get full and most likely all that insulation will just slowly fall down to the bottom. Do it right the first time, even if it means more work and more holes.
  5. You need 2 people and lots of time. We thought we could get all the walls, and maybe even our mudroom done in the 8 hours. However, my BIL was used to his high-powered machine, not this wimpy rental blower. It took 8 hours to do 2.5 walls (along with a long lunch break). You also need 2 people: 1 to run the hose and 1 to run the hopper (break apart the insulation, make sure it moves down into the hatch, etc.). Luckily our machine had a very long hose and a very long control switch cable so the BIL could turn it on/off from his position.
  6. Don’t open the hatch the whole way. You only need to open the slot about an inch or two to let enough insulation out that won’t overwhelm the system. You also need to make sure the cellulose is broken into small enough pieces as the “agitator” on the machine won’t do the job for you.
  7. Don’t overstuff the walls or else you’ll blow them out. When the wall was full, the blower made a different wheezing sound and you could see insulation wasn’t blowing through the tube. But some blowers are powerful enough to blow out the wall and start blowing insulation into the house.

If I think of any more, I’ll add them.

Cost of Insulating Our Exterior Walls

This is where we really lucked out. The original estimate of 700 sq ft was to cover the front (1 floor) and 2 sides (2 floors). We ended up just doing the first floor.

– I rented the insulation blower for about $60
– I bought 22 bricks of cellulose to cover that amount, which cost about $220. (but there’s a federal tax credit!)
– We would have used the whole bag of plugs at about $60 per bag.
– The drill and drill bit, if you don’t have them, would run around $60-80, or more.
– The siding tool is about $5.
Total for our materials was about $400-$500, counting the miscellaneous items. But we only used 12 bags of insulation, and less than a bag of the plugs, and my BIL had the drill and bit already.

But where we lucked out is that my BIL did not charge us for labor (which was very unexpected, and appreciated). I asked him “How much would you have charged us for this whole job otherwise?” and he replied “About $1000“. That includes all materials and I believe just him doing the work (but with his machine). Factor in diesel for his F-250 truck and we saved mucho dinero on our project!

How much will we save each year with this insulation? I don’t know because I really hate doing math, but just the fact that my toes won’t be chilly and my wife won’t be complaining are more than enough incentive for me. The fact that it was a relatively easy 1-2 day job is nice. And since my only cost is materials is a bonus.

But Wait! There’s a Tax Credit for Insulation!

See the chart below from about the federal tax credit for 2009. We’ll get about $40 back (30%) on the $120 we spent on insulation, but at least it’s something.

Product Category Tax Credit Specification Tax Credit Notes
Insulation Meets 2009 IECC & Amendments 30% of cost, up to $1,5001 FAQ on Insulation

Check to see if you have Home Performance with ENERGY STAR in your areas. Adding insulation to your home is covered.

1Subject to a $1,500 maximum per homeowner for all improvements combined.

About the author

Clever Dude


  • Nice job!

    We ran into the same thing on our house. It was built in 1954, no insulation in the walls. We contracted it out to the people who put the siding on and it ran us about 1000 dollars installed for our 1100 sq foot house (filled walls and added about 14″ more in the attic). They did it cheap, but they hosed us on the siding, so it all came out in the end.

    End result: our average combined gas/electric bills during the winters (KS winters are around 20*F) and summers (KS summers are over 100*F daily) are around 40% less than they used to be. Winter is especially noticable, you don’t feel the chill of the cold north wind penetrating the walls anymore. Also contributing to that 40%, I pulled off all the trim around the windows and squirted foam insulation in the cavities around the window casings… also helped seal up the house.

    Alot of work, but so worth it.

  • Good job! We are replacing some older windows with double-paned low VOC versions. Also, we’re looking into using recycled denim insulation in the attic. My boyfriend has major allergies so we have to be as “green” as possible. Next up is to change the radiator in the bathroom.

  • Our walls are insulated, but I have to add a layer to our attic before the winter is here. Coincidentally, I have the same gray Dutch Lap siding on my house.

  • Just blogged about it today. I’m $1800 to insulate my walls. BUT get this i’m getting 75% back from my energy company National Grid so OOP I’m paying only $500 to insulate 2 stories of my home! YES!

    And I still get the federal tax credit.

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