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Community and Q&A

RetroFoam vs. Cellulose Wall Insulation

1908Mitchell | Posted in Energy Efficiency and Durability on

We just bought a 1904 Foursquare in Seattle. We have already insulated the attic (cellulose) and are moving on to the exterior walls. We are getting some competing opinions on what material to use.
1) we have a little kid and 2) we have lath and plaster walls

From the pro-cellulose camp we’ve heard:
Retrofoam can shrink until it sinks to the bottom of the wall cavity leaving a powder, and that the chemicals used in the materials can have off-gasses. The folks that sell Retrofoam say it’s an organic material and will not have off gases.

Pro- camp:
Cellulose can cause a lot of dust and often expands/puts pressure on the interior walls that can crack the lath and plaster walls and do permanent damage. Cellulose, though recycled is treated with chemicals to make it fire retardant, and these chemicals are hazardous.

While we are planning on redoing the walls as well, we don’t want to cause any more damage to them. We also want to make sure our kiddo doesn’t inhale a bunch of dust or chemicals. We aren’t living in the house right now and won’t be until after the insulation and a bunch of other stuff is complete.

Any ideas about which insulation to choose? The walls are empty right now.
Thank you!

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  1. aaron55 | | #1

    I don't know that much, but have an old home like you, and I've read that insulating old walls must be done with care. You can cause moisture problems, as the house was designed to dry through ventilation in the empty walls. Someone will chime in, but I am also interested in this topic, as I have plaster walls with wood lathe. I also have painted wooden siding. I've read that it can start peeling paint if you insulate without providing a ventilation channel on the exterior of the insulation between the insulation and the wood siding.

  2. aaron55 | | #2

    Did you insulate the attic walls or the attic ceiling/roof with cellulose?

    1. 1908Mitchell | | #7

      We insulated the attic floor with borate-treated cellulose. We are not insulating the roof/ceiling.

  3. Expert Member
    Akos | | #3

    Insulating old houses is not usually about the type of insulation but the details of the exterior WRB and siding. Lot of times WRB is non existent or insufficient which can cause water to get into walls and create a lot of issues.

    I'm not sure where this cellulose is toxic bit is coming from. The typical treatment of cellulose is borate which is a very benign substance. Dense packed cellulose does a pretty good job of limiting any airflow inside the walls, if there is some dust in there, it won't get into your house. I've done dense packing and about the only dust is during the install. The improvement in comfort on an old house is incredible.

    GBA has a bunch of articles on dealing with old houses (stucco, walls with no sheathing or walls with no WRB), I would read through that and follow the suggestions there. Overall theme is if doubt, leave an air gap behind the sheathing on the interior and insulate with your choice of insulation. All work just as well.

    1. aaron55 | | #4

      Akos, to be safe you basically have to either remove all of the siding or all of the interior plaster to be certain you won't have water issues right? There's not a way to insulate with keeping the siding and inside walls intact?

      1. Expert Member
        Akos | | #6

        First you need to find out what is in your walls. Once you have that you can figure out which way to go.

        Generally if your walls don't have a WRB, leaving it as is is your best bet unless your doing major interior reno or replacing the siding.

        If you have a WRB, you might only need to fix some flashing details around doors and windows and can insulate by dense packing the walls. If you exterior is old stucco, that is a whole other beast that should generally not be prodded.

        1. 1908Mitchell | | #9

          I know that the walls are empty and have never been insulated. I don't know if there is a WRB. I'm guessing there isn't. It's too cold in the house to leave as is. We are replacing all the windows, adding insulation to the attic. We have vinyl siding (5 years old and installed by the previous owner). How do we find out if we have a WRB. The house hasn't had any significant updates since 1965.

    2. 1908Mitchell | | #10

      thank you so much! I'll take a look at these articles. the siding is recently installed vinyl (2018). Any ideas for how to find out whether the house has a WRB before starting the installation. Do I need to just take off the siding to find out?

  4. user-6623302 | | #5

    Blown-in cellulose can be installed from the inside or outside. Outside, siding is removed, holes drilled, insulation is blown in, siding replaced. Inside holes are drilled, insulation blown in and holes repaired. Cellulose is not dirty or unsafe and is a good moisture manager. What are you doing to your outside walls and what is the siding?

    1. 1908Mitchell | | #8

      We have vinyl siding -- installed by the previous owner a few years ago. We plan to keep it and replace it at some later date (5-10 years). The company that will install the packed cellulose insulation said that the blown in insulation could cause our lath and plaster to bulge or crack. We will likely retain the lath and plaster inside of the house (there are decades of paint and wallpaper on the walls at the moment, but taking off the wallpaper and skim coating will be less expensive than drywalling everything. Our other choice is injection foam -- Retrofoam. I've heard that injection foam can create a vapor barrier. Is that the same as the WRB?

      1. woobagoobaa | | #12

        Vinyl siding replacement in 5 years? I would determine what is under your siding (to at least the sheathing). If you are lacking adequate water and air barriers, perhaps tackle the exterior first. For example, if you have loose fitting Tyvek and gapped board sheathing, I would consider installation of a self adhered WRB.

        I'm falling back on the building science folk's 4 control layers. Water, air, vapor, thermal. The first two are higher priority than the others.

  5. maine_tyler | | #11

    WRB stands for weather resistive barrier. Think tyvek, tar paper. It's not generally performing the same job as an interior vapor retarder. Lots of info on GBA (use Google to search GBA by typing after your key words in Google search.

    One would hope that if new siding went on in 2018 they installed a wrb, but to check find a place you can pull back some siding (maybe a corner) and see what's between the vinyl and the sheathing.

  6. user-6623302 | | #13

    Blown-in cellulose will not blow off your inside walls. Get someone else to do your work.

    Vinyl siding is easy to remove and reinstall. Like Tyler said, some exploration is in order

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