GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Blowing Cellulose into Older Walls

John | Posted in General Questions on

Hi There,

New to this site, it was recommended this is a great place to get advice for home renovation questions answered. I live in an older home, that had 2×4 framing, but no wall insulation. I was researching the option of retrofitting cellulose. Is this a good option? I have also seen some write ups suggesting it isn’t good. I have plaster walls, apparently people have said issues could arrive without a vapour barrier such as mold or structure damage to framing. Is this true? I’ve also heard certain paints and primers can act as vapour barrier, is there good evidence to suggest they work well? Trying to lower my heating bills and feel like it’s not freezing in my house in the dead of winter.

Hoping someone has some advice for any of my questions above please and thank you.


GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member
    Akos | | #1

    Generally the problem with older houses is not the plaster and lath on the inside or vapor barrier. The issue is a lot of times a lack of sheathing (ie siding nailed right onto studs), missing or damaged WRB and lack of proper flashing around windows and doors.

    If your place doesn't have any of the above, generally the walls can be dense packed. I would not even contemplate insulating a house unless all the issues are fixed. Sometimes, leaving the walls as is until major interior or siding work is needed is the only option.

    Even if your water management is good, insulating the walls will significantly reduce the drying capacity of the siding. This can sometimes cause the older oil based paint on the siding to peel.

    1. John | | #4

      Hi Akos,

      Thank you for the reply. I do know the house does have sheathing, how could the condition is overall is hard to know as I can't see. It's 2x6/2x8 planking nailed into the 2x4 studs, with a tar paper otter facing, and appts 1" gap for air/water drainage. The outer cladding is one layer of brick. Based on that bit of information, does it make sense to dense pack or leave the cavities as is and only if I pursue tearing the old paster walls down, would it be viable to insulate at such time?

  2. user-5946022 | | #2

    Welcome John.
    So that you can get proper help, please tell us:
    1. What region of the country the home is in
    2. What is the construction of the wall, from inside to outside. You have already indicated inside is plaster, is it 2x4 or 2x6 wood framing? Is there sheathing? Is there a vapor barrier or tar paper? is there wood siding or masonry on top of that? If masonry, is there a consistent gap between the back of the masonry and the outside face of the sheathing?

    Regardless of the above, the greatest impact to comfort in your home in winter will be from air sealing. Some of that may occur with insulation, but it is usually best to address as much air sealing as possible before insulation. Do a search on this site for air sealing and start reading some of the articles. And again, welcome!

    1. John | | #3

      Hi CL,

      Thanks for your reply and welcoming to the site! I'm actually located in Canada, Toronto , Ontario. So we can have harsh winters and hot/humid summers.

      The wall makeup is 2x4 stud wall, (lathe and plaster on the inside as mentioned which you know) plank sheathing on the outer side of the 2x4 studs which looks to be 2x6, perhaps with with some 2x8 also. It does appear to have tar paper on the outer side face of the sheathing, with approximately a 1" gap or so for water/air drainage. The house exterior is brick, one layer. Hope that information helps and allow you to get a better sense of the walls. Let me know your thoughts, thank you.

      I will definitely look into the air sealing as well, I think most people get wrapped up focusing on insulation more than anything else, which includes myself, so I will look more into air sealing as well, thank you for that advice!

  3. Expert Member
    Michael Maines | | #5

    Based on your location and details provided, it is probably safe to install cellulose insulation. It's much harder to fully fill cavities with the proper density in existing walls than with new walls, but experienced installers can usually do a pretty good job. If there is a bit of moisture accumulation, the cellulose should have a borate additive that protects both the cellulose and the surfaces it touches from mold and microbial growth.

    1. John | | #6

      Thanks Michael. What are your thoughts on primer/paint vapour barriers? Any knowledge or experience and do you know if they do a reasonable job?

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |