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any advice about insulating walls in an old house?

awefea | Posted in Green Building Techniques on

i’d like to not have to tear out the interior walls. foam products inserted from the top might expand too fast and not make it to the floor. someone suggested pouring in vermiculite between the studs. i’d really appreciate suggestions/advice. thanks, robin [email protected]

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    I've heard some horror stories about folks who poured foam down into walls that lacked sheathing and a house wrap or drainage plain. The foam held wind driven rain against the back of the siding which also wet the studs and caused serious rot problems. I'd have a similar concern about cellulose in this type of application. So I am going to recommend blown-in fiberglass due to its advantage when drying potential is the priority.

    But first lets make sure all your forced air heat and air conditioning ducts and air handling equipment are properly sealed with Duct mastic. when you look at your ducts they should be slathered at all the joints with white or gray goop we call Duck Butter. It goes over the duck tape to cut down on quacking and leaks. It also should seal the ducts to the sub floor and should back up the metal joints in the air handler. It's messy to use where the ducts come through the sheet rock so those locations generally get caulked with an acrylic painters caulk.

    Next, I would encourage you to go after the ceiling and floor planes. If you have fiberglass on the ceiling you may be able to pull it back and caulk all the drywall to wood transitions at interior and exterior top plates using a canned foam like Great Stuff. then you can replace the insulation and blow enough cellulose over the top to get to an R-38 or more. Once you are blowing cellulose the added thickness is very affordable.

    Then I would seal the crawlspace and insulate the crawlspace walls while being sure to leave a apace for termite inspection at the top. The plastic should be a minimum of six mil thick. generally we use black or white on the floor so we don't have to look at water droplets that condense on the bottom of the plastic in the summer. We use clear on the walls so we can see any creatures making their homes there.

    After that I would caulk the windows and siding where rainwater is getting in and look carefully at roof and chimney flashings again to be sure the inside is staying dry.

    Only then would I start to consider filling the walls with insulation.


  2. Daniel Morrison | | #2

    How old a house are we talking about, Robin?

  3. awefea | | #3

    WOW! i really appreciate your very detailed and comprehensive advice, michael, but that all sounds to me like it would be easier to tear out and replace the walls! the house a 1949 box (surrounded by many acres of exactly the same original house for the returning vets - i was told that they were of sears origin) with actual 2x4" wood framing, wood floors, a paneled basement (which was easy to insulate), concrete asbestos siding (which has been just fabulous, but it's dark red so absorbs a lot of heat in the summer), and little clumps of what looks like lambs wool between the interior and exterior walls. (i had all new double-paned windows put in a few years ago and was appalled by the lack of insulation!) i plan to grow vines up the south side of the house this summer but i know insulation would also make a huge difference. i was only able to get a small home equity loan so i don't have much $ to work with and had hoped i could deal with the insulation myself and put the $ towards the pop-out we want to do to the garret upstairs. but i'll have to get some help and just do one thing at a time ....... thanks again, robin



    I did not mean to overwhelm you with more information than you needed, it sounds like you are well along with the draft sealing in the basement and new windows. I just wanted to be sure you had that done that work first as we have a saying "it doesn't matter what R-value is in the wall if the door is open"

    Once you have your draft stopping done and ceiling plane insulated and duct work sealed up, which it sounds like you've already done, then it does make sense to insulate your walls. As much as most extreme green folks would want you to remove your siding and double wrap the whole house with foam board and fur out your windows and re-side I can see that what you want to know is what kind of insulation to pour down between those studs.

    Vermiculite does sound very enticing here, better in my opinion than foam or cellulose in the drying potential but I'm going to recommend blown-in fiberglass as the best value and least likely to have un-intended moisture accumulating and rot potential.

    This is likely to be worth hiring a pro to do. I would recommend going in through the interior walls so as to avoid damaging the weather protection capability of the asbestos siding as much as to avoid drilling or disturbing it in ways that might release asbestos and lead paint. I think it will be less expensive to repair al zillion holes on the inside even if it is plaster rather than wall board than to try to repair all those holes in the exterior siding.

    I'd say to go after the easier stuff and understand that filling the walls with out stripping them back to the studs is likely to be a "good enough" kind of a fix. if you get 80% of the spaces stuffed with insulation you are doing pretty well.

    I think you would do well to have a blower door and duct blaster test done first though. you may have gaping holes in the ceiling over kitchen soffits and so forth that would be easier and less expensive to address than the wall insulation. You've done a lot of work already, some measurement might point you to the biggest energy villains, and they may turn out to not be the walls even still.

  5. gbauser-20428 | | #5

    I agree that an energy audit is an excellent tool to include in the type of energy and comfort performance upgrade you are doing.In my area more and more energy raters and auditors have incorporated the use of infrared cameras in their testing process. Thermograhy is especially helpful when assessing the integrity of your air sealing and insulating efforts. Used alone or in conjunction with a blower door, an IR camera will quickly identify voids and areas of leakage. The images are really dramatic as "weak" spots will light up like a Christmas tree.
    Many utility companies and municipalities are offering rebates and funding for auditing costs as well as funding for insulation, HVAC, and water heating upgrades. Good luck with the project.

  6. awefea | | #6

    well michael and jeff, i truly appreciate your various pieces of great advice. i had intended to do holes in the interior walls from the beginning but will definitely look into blown fiberglass. is it a liquid which hardens or just loose fibers which will fill in whatever space gravity pulls it into? i believe i had a blower assessment and follow-up by our local power company a number of years ago and there's really nowhere in the house that's drafty - just cold walls in the winter and "uncoolable" heat radiating into the house in the summer. the difference the insulation has made in the basement this winter is really amazing and pulling off the paneling and nailing it back was not a big deal. next for me is the first floor walls and then radiant barrier insulation in the upstairs rafters. you guys are awesome and i so appreciate your support! thanks again, robin

  7. studio513 | | #7

    Sealing the joist band and basement is first, but presuming that has been done, I would consider doing a more significant upgrade on the exterior. The asbestos siding is one of those things that is going to have to be dealt with sooner or later. It's pretty inert until it gets cut, so don't cut it. Wrap the building with taped off housewrap, screw on 1.5" foam [with 2" plastic washers], screw OSB over the foam, and reside.

    This is a Big Fix, and it might be more than you're looking for, but it will yield substantially increased insul values by eliminating transission thru the framing while at the same time getting rid of the asbestos problem. And that IS a problem.

  8. Riversong | | #8


    It doesn't sound like you're looking for the BIG FIX, as Tom proposes. And cement-asbestos siding is NOT a problem as long as it remains intact.

    I will have to disagree with Michael on his recommendation for blown insulation. If the stud cavities are sufficiently open to air circulation as to take advantage of fiberglass' ability to dry by convection, then the fiberglass will offer little insulation value. And fiberglass loses R-value when its temperature either drops below or rises above room temperature.

    If the exterior cladding is in good condition and precautions are taken to caulk and seal all exterior penetrations, then I would suggest blown dense-pack cellulose (3 pcf or better). Not only will this offer better R-value than fiberglass, but it will also reduce air infiltration/exfiltration.

    The hygroscopic quality of cellulose (highly absorbant and able to safely store and release up to 30% of its weight in water), would likely be an advantage over fiberglass which will allow environmental water or condesation to drain and collect at the bottom plates where most mold and rot occurs. Cellulose, acting as a moisture buffer, can actually protect the wood framing from reaching the 80% moisture content which precipitates mold growth.

    Cellulose is also the most green of all commercially available insulations (fiberglass is a known carcinogen), is extremely fire-resistant (with typical borate additives), is an irritant to rodents, and will kill most common household insects even though it is completely non-toxic to humans.

  9. awefea | | #9

    very interesting advice robert. i will forward this info to my sister, the architect, who is helping me with the addition upstairs. i am particularly excited about the non-chemical "green-ness" of cellulose. as i have asked before(since i am on a small budget), is the cellulite a material which i could install myself? you mention "blown dense-pack" cellulose. can you tell me more about it, and do you have a mfgr in mind? many thanks, robin

  10. Riversong | | #10


    Cellulose installation requires a good blower (special machine for this purpose) and the experience to do the job properly. Installed cost tends to be between fiberglass (cheapest) and sprayed foam (most expensive).

    You'll need to find a local installer. The cellulose I've always used is Cel-Pak by National Fiber (, but I don't know if it's available nationally.

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