Interior Storm Windows
Blowing in Insulation
Insulating a range hood fan
Sealing a Bulkhead Door
Top Bar Bee Hive
Wooden Box

Blowing in insulation

Infrared picture of house, before
Infrared picture of house, before.
photo credit: Topher Belknap

I am often asked what energy improvements homeowners can make themselves. I am now here to tell you that blowing cellulose insulation into your walls is one of those things. While blowing insulation into an attic is a common do it yourself project, this is a job which is often recommended for professionals only, but Mainers are skilled and resourceful people and if I and my sweetie can do it, so can others. This is not intended as a how-to, but rather as an inspirational article.

Here is a picture of our house, taken with an infrared camera (one of the tools we use for energy audits). One of the things you will notice is that the windows 'have ears', as my sweetie put it. That is, there are warmer patches visible around the top and bottom of each window. This is an indication that the insulation is lacking in those areas. The exact reason for that is related to the unusual way my walls were constructed, something called a Larsen Truss (invented by Jim Larsen). The walls are about a foot thick and contain a lot of insulation. However, when the house was built the insulation contractor failed to fill some areas, particularly around the windows. When I turned the infrared camera on those areas the problem of cold spots my sweetie complained about, became immediately obvious. With all these picture cold is black, then purple, and orange, with yellow and white being the hottest. The temperature in the upper corner is for the spot where the crosshairs are, and the temperature scale is at the bottom. Exact temperatures aren't important here, we are looking at relative differences.

It should be noted that an infrared camera is not needed for this job. The important thing is knowing where you don't have insulation, which can be determined by inspecting around electrical outlets, or by drilling holes in the wall in inconspicuous places, by inspection from above (for balloon framed houses), or simply by noting where cold places are, either with a hand, or a cheap IR remote thermometer (around $25-$40). The main purpose for using the IR camera, was to document the before and after conditions.

For other houses the problem may be different. Old houses probably started life with no insulation in the walls. If nothing has been added since, then they are prime candidates for this technique. All the empty space in the walls will need to be filled with insulation.

Stud bay missing insulation
Stud bay missing insulation before.
photo credit: Topher Belknap

Here is a picture of one of the places where I could use some more insulation (taken from the inside). As you can see there is a large space here, more than can be explained by settling. So, the job is to fill that space with insulation. Insulation can be blown in from the outside, or from the inside. The choice comes down to which will be easier to get to, and easier to patch once done. For me, the interior is not painted yet, so going from inside was an easy decision.

Blowing cellulose insulation is a messy dusty job. So the first thing was to cover as much of our stuff as possible, since it all needed to be moved away from the walls to gain access, We moved it to the center of the room and draped it with cloth, and plastic sheets. I also got my respirators out; dust masks are only marginally useful, respirators with filters are recommended. Safety glasses, and grubby clothes are also a necessity. I also planned on us eating out of the house for a few days. I cut the holes in the wall with a 1 inch hole saw in an electric drill.

We rented an insulation blowing machine at a local rental place. The insulation was acquired at a home improvement store (which often rent or lend blowing machines as well). The machine is heavy, so I was lucky to have a neighbor to help move it into place. Sane people would be doing this job on a calm spring or fall day and will have the machine outside. Being the dead of winter, I put it inside. It came with fifty feet of hose, a nozzle for the walls, and a remote switch to control it. The bag label provides some advice on how much insulation is needed to acheive a given R-value for 1000 square feet, but since I didn't really know how much space I had, I just took a wild guess. And then went back later for as much again.

Stud bay after filling with insulation
Stud bay after filling with insulation.
photo credit: Topher Belknap

I ran the hose and remote switch, my sweetie filled the hopper with cellulose from the bag, and tried to keep the hose and remote cord from getting too tangled. It would have been much harder or impossible with only one person. The machine had a control to set the air-insulation mix, I found that full open was the best setting for me. The main trick was knowing when the cavity was filled. If I left the blower running too long, the nozzle filled up and needed to be cleaned out (having a short dowel to hand helped take care of this). It took an awareness of the sound from the walls as well as sound of the blower on the machine to know when the space was full. After I had gotten about a quarter of the job done, I was able to get each bay filled with few issues. Here is the same wall as the previous picture, only this time properly filled with insulation. The holes were then filled with spray foam insulation to get a nice vapor seal. The extra was sliced off flush with the wall. Subsequently they will be patched over, probably with drywall compound.

The mess can be kept to a minimum by making sure that the nozzle remains in the wall until the blower has come to a complete stop. Removing a little before, or if it seems clogged can end up splewing dusty insulation everywhere. The insulation contains borates to retard fire and pests, and it is not something you want up your nose.

Infrared picture of house, after
Infrared picture of house, after.
photo credit: Topher Belknap

Here is a picture of the house after all the work was done. Note that there are still some places that didn't get fixed (under the center windows for instance) do to accessibility issues. On the whole though the entire house is mostly a uniform color. Since the camera adjusts to a given temperature range, this is the appropriate result. The fact the temperature is 17 degrees lower on the after picture is just an indication that it was colder outside that night.

The whole project (not including prep and clean up) took about 10 hours (spread over two days) and we put 13 bales of cellulose insulation into the walls, which the chart on the package says would be enough to do 722 square feet of 2 x 4 walls (to achieve R-13). For this house, we took perhaps 180 square feet of area from around R-2 (no insulation) to R-45. This should amount to 12 Million BTUs saved every year, equivalent to about 85 gallons of fuel oil. At today's price of $2.47 per gallon, that amounts to 210 dollars. The cost of the project was as follows:

Blower Rental1 weekend$55.00 $55.00
Cellulose insulation13 bags$11.30 / bag (including tax)$146.87
Spray Insulation1 can$10.30 / can (including tax)$10.30

So, a simple payback of about 1 year. That is, I could have bought oil this year, or for the same money made this fix, and saved this amount every year from now on. Of course, all situations are unique, so another house would get different results, however for houses without insulation in the walls, this is almost certainly a huge win.

Infrared picture of front door
Infrared picture of front door.
photo credit: Topher Belknap

Next Project

This picture highlights my next project. This is my wooden front door, complete with storm door. As you can tell it is warmer than the (admittedly high-efficiency) window right next to it. It is therefore losing a lot of heat.