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how to install cellulose insulation

December 10, 2005

My 1930 house has no insulation in the walls. I would like to add some cellulose insulation in exterior walls. All the drywall is off and the shiplap walls are exposed; I have a couple of the interior boards off the top of the walls to get access to the cavity. (1) How should I add the insualtion? In two places in the walls there is old wiring (knob and tube, I think). (2) Is it ok to put insulation there? The big-box home supply store said it is treated so it should be ok.

Comments (15)

  • redhouse

    It is not safe to put insulation in a wall with knob and tube. What happens is that moisture will collect on the insulation and set up a potential path between the two legs of the knob and tube wire. I wish it were not so I have the same problem!

  • bungalowbees

    You may wish to call your local fire dept for tips. I did and they were only too happy to offer their thoughts! It was years ago and I decided to put rock wool in the attic and rewire to code. The combo of attic insulation & high efficiency furnace paid for itself in just over 2 years. We're warm & I sleep better.

  • appletnc

    I am also considering retrofitting the exterior sidewalls of my house with blown in cellulose product called Cocoon (sold by Home Depot). However, the drywall/plaster has not been removed. So I will be drilling holes in the walls and blowing the insulation into the stud bays.

    - Does anyone else on the forum have experience retrofitting drywall covered sidewalls with Cocoon or another brand of blown in cellulose insulation?
    - Since removing the vinyl siding is difficult to take off one piece at a time, I will most likely drill holes on the interior of the walls, blow in the insulation and then patch the holes. The instructions (http://www.cocooninsulation.com/homeowners-retrofittingsidewalls.asp) say to drill two 1" holes in each stud bay, one three feet from the floor and another one foot from the ceiling. Two holes seem like overkill, why not just just drill one hole near the top of the stud bay and fill from the top?
    - What's the best method for filling the 1" holes? The Cocoon website says to use foam or wood plugs, should I plan to make my own plugs or can the be bought?

    Any advice and/or suggestions are appreciated. Thanks.

  • chuckr30

    Cellulose may pose a fire hazard with older wire with a woven fabric coating. I have that type of wire and mine is frayed and just looks dangerous. Not only that, but I had a brand new house before this one, in 2003, with 6" exterior walls with cellulose in the walls. I swear a candle would blow out if you placed it close to the wall the draft was so bad. I believe that the cellulose, over about 7 years (house built 1996) compacted and became ineffective. Thus I would not use cellulose in the walls.

    Perhaps use fiberglass or a spray expanding foam which is sticky. (Not the stuff in the cans.) There is a foam which can be sprayed on by pros which does not have the odors or fumes the earlier foams had.

  • appletnc

    After reading a few other threads, I have a couple additional questions. I'm pretty sure that my house doesn't have a vapor barrier on the outside. I'm planning to blow cellulose insulation into the wall from inside. Will not having the vapor barrier be an issue?

    I'm still looking for answers to the questions I posed earlier in the thread, if anyone has any answers or advice it would be greatly appreciated.


  • scrad750

    Hey appletnc. fire hazard with old wire a yes. I checked with my fire department as well. Replace old wire before going down walls.

    I did blow insulation myself in my 100 yr house down the walls.I did it upstairs and down stairs and in the ceiling. I never did it before, but it was a little messy. I only drilled 1 hole at the top not at bottom. I don't know why they said put one at bottom. I had a guy whose done it many times give me some advise. He never mentioned to do that. I did take off the siding instead of doing drywall. I tried one room inside the house and it took me awhile to get all those holes looking smooth again once I patched them. I ordered the plugs from lowes. I filled the cavity. Put in the plug and back on with the siding. All the mess stayed out side..

    It made the world of diff. down stairs. Upstairs it helped some, but i think my heating unit is to small. Ps. It was much quicker doing it from outside than inside. If you compare to cutting holes in walls, plugging, remud, sand , remud, sand, remud , sand and paint. Verses take siding off, cut holes ,plug, put siding back on. No sheet rock dust or insulation in house.

    Hope this helps.

  • appletnc

    Scrad750, thanks for the info that is very helpful. All of the wiring in my house has been updated to Romex, so that shouldn't be an issue.

    Did you worry about a vapor barrier on the outside of the wall?

  • appletnc

    One more question: I have vinyl siding, if I wanted to blow in the insulation from the outside, is it possible to take off a single course of the vinyl siding near the top of the wall? I've never really played with the siding, but I thought it locked together in way that made it impossible to take down course in the middle of a wall.

  • kevinw1

    Do you live in a climate where it's normal to put a vapor barrier on the outside? In heating climates the vapor barrier goes on the inside - the warm side - to stop water vapor getting into the insulation and condensing there.

    New construction does put an *air barrier* - housewrap - on the outside, under the siding, but that has to be vapor permeable so that any moisture which gets into the walls can dry to the outside. A vapor barrier on inside *and* outside is a recipe for rot in the walls.

    Incidentally, I have blown-in cellulose in my 1930's house outside walls, installed who knows when - 1970s maybe. In opening up a wall recently that exposed the insulation it has settled a little at the top (or the installation left a gap at the top - quite possible, since they completely missed doing under some windows) but apart from that it's in excellent shape, well packed and filling every nook and cranny.


  • kurtronix

    appletnc, you can do just that, zip off the siding, drill and then blow it in. I did just that this fall. I did however drill 2 holes per cavity as was recommended to me. I guess there is a greater chance that the walls won't buckle with the air pressure AND a greater chance of acuratally (sp, sorry) filling it to the correct level. Hope this helps...

    As always...YMMV

  • bozo_boxer

    You would be better off rewire your house since you got the dry wall off then insulate.I am sorry but it isn't as easy as it seams to drill holes and insulate.The hose keeps clogging up on the smaller holes and have to keep unclogging the nozzle.When we did the inside remodel we ended up drilling 3 inch holes to keep from clogging the nozzle.Another tip is to get the insulate to pack tight use a pvc elbow on the end of the hose so you can put it in the hole and it will aim down into the cavity instead of hitting the outer wall and just dropping down into the hole.This does make it alot easier and alot faster to boot.

  • terryr

    My dad helped me do this in our old house last spring. Electrician said it was fine to do. Ours is a balloon construction. We drilled a 1" hole between each stud and under the windows. We didn't have that much trouble with the hose clogging (what clogged the hose was pieces of plastic in the cellulose). I bought my bags of cellulose from Menard's and they supplied me with the hopper (or whatever it's called). The hose was long, it had an adapter to put on the end, that was a metal thing, looked sort of like a funnel. The hopper stayed outside, so the mess was outside also. My experience wasn't like bozo boxer's at all! It was easy!


  • julieanne76

    We have lived in a circa 1921 Colonial Revivial home for the last 10 yrs. When we moved in, all the plumbing and electricity had been updated. We have been "socked" in the pocketbook every year by high utility bills. I have read bad things about "blow in" insulation that it sinks and is a waste of time. The only other alternative is to gut out 2300 sq ft of plaster and lathe and start from scratch. We really don't want to go the the time and expense that will take. We have full time jobs and 2 kids in college...so you know where the money is. I have read on this forum that you can install blown in from the "outside" of the house. Another stumbling block for us. We have the old asbestos siding. If you try to pry it off, it will crack. Bad news. Please give us some advice!! If my natural gas bill is over $400.00 again next month I will go bonkers!

  • sharon_sd

    julieanne: You can also blow in insulation from the inside. This is how it was done almost 25 years ago in our stone house. Make sure also that you caulk all the places where air leaks, and have good gaskets on your doors. Air blowing through isulation is only slowed down. If you have air leaks it will still feel cold, especially on windy days.

    When we insulated, caulked and installed storm windows, our heat costs were 1/2 of the prevous owner's bills. they went down another 1/3 with a high efficiency furnace.

    Consider getting an energy audit done. These companies will advise you on what would be the most practical and cost effdective steps for you to take.

  • petermn4

    I am planning on using blow-in insulation to provide better insulation in the attic of my 1927 home. What is the best way to estimate how many bundles I will need? I've done it before, but it was as an employee for a remodeling company where I didn't have to do the estimating.

    Also, I've read great information on using blow-in insulation to do existing exterior walls. I'd also like to do mine. I'm pretty sure all they have is a few layers of old newspaper. Two questions: How do you do it from the outside (my preference) when you house is stucco? Should I worry about the old newspaper being in there also? I'm also thinking about re-surfacing my stucco with a thin layer of stucco, so maybe that would be the best way to cover up the whole marks.

    Looking forward to hearing some good advice.

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