How To: Insulate an Old House

By Scott Sidler April 28, 2014

how to insulate an old house
Image credit: mistac / 123RF Stock Photo

I get asked a lot about insulating old houses, especially in the wintertime. It makes sense. People fall in love with the character rich architecture of these homes, but they don’t want the crazy heating and cooling bills that come along with that character.

Chances are good that if your house was built before the 1960’s there is little to no insulation. Before the energy crisis of the 1970’s energy was abundant and cheap in America and it was cheaper to heat your old house than it was to insulate it. Today, things have changed and to save yourself lots of money it’s a good idea to learn how to insulate an old house without destroying it.

Before you start, check out the EnergyStar website to see what the recommended levels of insulation are for your climate zone.

You have lots of options as far as materials you can use and I won’t go into too much detail about those here. You can read all about the differences, performance, and pricing in my earlier post All About Insulation. For the purpose of this post I’m going to be speaking about blown in cellulose and batts since they are the easiest to retrofit into an old house, but just know that you do have other options.

Insulating the Attic

Before you do anything else this is where you should begin insulating, especially if you live in the hot southern states. The majority of heat loss and gain occurs in your attic.

Read more about the 3 types of heat here.

The attic is often the easiest place to add insulation. If you have an unfinished and unconditioned attic like many old houses my first recommendation would be to add batt insulation on the underside of the roof.

Measure the size of the roof rafters. Are they 2×6, 2×8 or bigger? The bigger they are the thicker the insulation you can fit. You’ll also need to determine the spacing of the rafters. Are they 16″ O.C. (on-center) or 24″? Sometimes they aren’t evenly spaced which means more work trimming your batts to size.

Here’s a quick tutorial on How to install batt insulation.

Once you’ve insulated the the underside of your roof it makes sense to beef up the insulation even more by blowing in cellulose insulation on the floor of the attic. This will help to keep the living spaces below more comfortable year round. You can rent an insulation hopper from most big box stores to blow in your own insulation with little difficulty.

The trick for blown-in insulation (and any insulation for that matter) is to fill as much as you can without compacting it. Insulation looses its insulating abilities the more it is compacted. It should be installed light and fluffy to work best.

Tip: Be careful not to block any soffit vents with insulation if they are present in your attic.

Insulating the Walls

“How can I insulate the walls of my old house without tearing down the plaster walls?” This is by far the biggest insulating dilemma faced by historic home owners. Can it be done? YES! You don’t have to tear down your plaster walls to insulate them. I’ll show you how.

The best way is to remove a course of siding or a few shingles from your home’s exterior. If you have a masonry exterior then sadly this won’t work for you.

Step #1 Remove & Mark

Remove two courses of siding from the wall. The first about a quarter of the way up the wall and the second just below where your ceiling is. If your house is more than 1-story you’ll have to do this for each story. Many old houses have diagonal sheathing underneath the siding. Some don’t but either will be fine. You want to find a wall stud. The siding should have been nailed through the sheathing and into the studs so use the location of the original nails as a guide. Mark the center between two studs. You want to be right in the middle of the stud bay.

Step #2 Drill an Access Hole

Using a spade bit drill a hole in the sheathing big enough to fit the hose nozzle on the insulation hopper (usually 1 1/2″). Stick a coat hanger in the hole and poke around to see if you are in the right place and adjust accordingly. Once you are certain you’re in the middle of the empty stud bay you can measure 16″ to each side of the hole all the way across the wall which should give you the center of each consecutive bay. You’ll need to drill two holes in each of these stud bays, one on the top and one on the bottom course of siding.

Step #3 Fill with Insulation

Fill the hopper with insulation, turn it on and start filling the lower hole with insulation. Once the hole is filled enough the machine will start to whine indicating that that portion of the wall is full. Pull the nozzle out of the hole and repeat the process on the top hole.

Step #4 Patch Up

Once you have filled all the bays with insulation we want to cover up the holes. I prefer to cover the hole with a small patch of adhesive backed flashing tape (aff. link). When the holes are covered nail your siding back into place and you’re done!

Occasionally you’ll run into blocking between the stud bays which will block off the flow of the insulation. It can be difficult to tell where and when this blocking is installed. If you have access to an inspection camera with a light to see into holes that’s the easiest way to determine where they are. It may require removing a few additional courses of siding to access these areas, but you’ll have to determine that as you go.

Insulating the Floors

If you have a basement or crawl space the best way to insulate the floors of the living space above is much the same as the attic, by installing batts into the stud bays of floor joists. It will be a slow process in tight crawl spaces, but once it’s finished you won’t have to do it again and your floors will be much more comfortable year round.

The one tip I’ll give you is that if you are insulating in a crawlspace make sure you have rodent proofing wire screens installed around any opening to the crawlspace. If you have critters able to access your crawl space they can make a mess of your newly installed insulation over the years. Rodent proof the crawlspace first then go about installing the insulation.

I really hope those tips help you to get the job done quickly and easily. You don’t need to go throughout expense and mess of tearing down all your walls just to insulate. That is one of the 5 worst mistakes of historic home owners, but with the information in this post I know you’ll be smart enough to avoid it.


58 thoughts on “How To: Insulate an Old House”

  1. I recently bought my first home, a duplex with a family member that was built in 1928, I’ve gone through several blogs and articles but cant quite seem to find a clear solution on how to get new insulation into my walls with out destroying the plaster, which is one of the reasons I chose this house. The house is very drafty and while I have been able to fix the windows best I can without outright replacing them but i can still feel the cols air coming through from outside

    As stated it was built in 1928 of brick but has vynle siding. Im wondering if I can simply remove the siding, Put up that pink sheet insulation and then put up the siding again to help or if this is just a temporary measure that wont solve anything in the long run or at all?

  2. Hi Scott,
    Really appreciate your helpful advice but… I have an old tobacco pack-house with heart pine flooring that I have converted into a nice 1000sf, two bedroom guest house. We insulated the walls and attic and in-between the floor joists with plenty of nice new batt insulation. We installed four Mitsubishi split duct units and a propane stove. We are able to crank out the heat but the only problem is it gets pretty chilly at floor level. The cold air seeps through the cracks in the old floor in spite of the insulation. I’m thinking about pulling out all the bat-insulation from between the floor joists and going back in with spray foam. If I do this, what type of foam should I use or not use? Thanks for your help.

  3. Hello Scott

    I have a house built 1959. I believe it needs more insulates . The house is a ranch style. In the attic there is some insulation on the floor. Should I batt the underside of the roof and blow more on the floor? Plus you say to batt the basement under the living space. My basement is half finished so could I blow insulation in or is batt better. Now blow the walls you don’t recommend?

    1. Yep, I would put batts on the roof deck underside and then blown in on the attic floor. If you can batt the crawl space that will be helpful as well. I’ve seen more issues showing up with blowing insulation into the wall cavities due to moisture intrusion so I usually stay away from that now.

  4. Thanks for this article. We recently got a new house that’s fairly old. We had it checked and it’s not properly insulated. We really invested in getting it insulated and did some renovations while we’re at it. No wonder it costs so cheap.

  5. This is great information. Thank you for publishing this…. Thank you I really appreciate the articles you write….

  6. Hi.. I have a house that was built in 1920. They extended the old porch to the living room. In the summer that room just doesn’t cool at all. Any suggestions bon insulation for that?

  7. I am still confused. Can I put batting in the rafters of my 100 year old house? It has no venting what so ever and has a metal roof over wood slats.

    1. I would say yes to putting insulation on the underside of the roof. You have to be more vigilant in checking for leaks though because wet insulation is an easy way to get mold and rot.

  8. Scott, I hear a lot about the negatives of blowing cellulose into the walls of old houses. The claims are that the moisture goes through the walls and gets the cellulose wet, causes rot and makes the paint peel.
    Your thoughts on that?

    1. Peter, I agree that this problem happens too often. Blowing insulation into the walls of an old house is not something to be done without thinking. It really depends on the setup you have and your particular circumstances on whether it may work for you. If in doubt I’d say skip it.

  9. I read an article on the internet that says that cellulose insulation in old buildings can become damp (because there are no moisture barriers, as you have in new houses). It then compresses and becomes a home for mold and can cause the wood framing to rot. I’m asking because I’ve just made plans to have cellulose insulation blown into the walls of my 130-year-old balloon-frame house.

  10. We’re looking at a Victorian house that still has one original wooden wall. It is right up against the brick building next door. It has had closed cell foam applied to the interior surface of the exterior wall. Would this be sufficient to weatherproof the wall?

  11. After putting up stud walls in the firstfloor and insulating them, I turned my attention to the second floor. My home was built in 1896 and it is a double brick wall construction. I would like to keep as much floor space as possible. The house is only 17 feet wide, Would it be better to strip the wall right down to the brick? If so what would you recomend?

  12. Hi Scott, I live in a pre 1920 folk Victorian in Columbus, Ohio. We got a couple estimates for whole home insulation and the contractors suggested using spray foam in our basement crawl space. Are there any concerns with using this material since we have a stone foundation?

    1. Jen there are some potential issues so you want to make sure you get a few opinions first. Spray foam can be tricky if not applied correctly, but it is also the best way to get the most insulation for your money. It’s hard to tell without seeing your setup what would work best. Just get multiple opinions.

  13. Scott, My wife and I just purchased an older home in Ainsworth, NE. It has Plaster over lath strip walls. It needs to be reinuslated and I don’t think it is balloon framing, but am not sure. I’m a 100% disabled vet, who is one handed and can no longer do the work totally. Would it be best to do some of the work myself, then have a contractor finish it. Or would it be better to have them do the total job? I don’t have a lrg income. and savings are low. Is there any help that you know of? Thank You.

  14. Hi Scott,

    I’ve seen lots of articles/blogs about adding insulation to plaster walls via holes in the walls from the interior or exterior. I was just wondering if it’s possible to add insulation to walls via the attic?


  15. Hi- I bought has house that has plaster walls that are in rough shape and the previous owners wallpapered and then painted over the wall paper so I am having everything dry walled. If there is no insulation in the walls can I drill holes on the inside walls of the exterior walls and do blown in insulation since everything will be covered with drywall anyway? Thanks

  16. We have vinyl siding and the builder did not insulate our interior or exterior like he should have the air blows in around Windows and even the walls are cold. How can we have our home insulated without taking off the siding and taking out the windows?

  17. Question. I have one upstairs room that has poor insulation, it is always hot. The house was built in 1990. The downstairs of the house is concrete block, while the upstairs is wood frame. What can I do?

  18. Scott, I have a rather peculiar (perhaps not, maybe it’s simple and it’s because Ive not dealt with this before) situation. My wife and I are renovating a bathroom in the upstairs of our 1870 Italianate. The bathroom would have been an addition after it was originally built. The water lines/waste line and stack vent run up along the north (coldest) wall. We’ve replaced them with pex pipe and pvc. We have also have a new electrical line we are adding from the circuit box in our basement to the attic to add new outlets to a couple of rooms and it follows the same path along the north wall. To access all of this we had to hear out about 18″ wide in the 1st floor room. So now we have the task of insulating. We are using a basic roll, not blowing since it’s exposed to the studs (it was drywall, not plaster). I am thinking since its the north wall and it gets the extreme cold (Illinois) weather I should sandwich the new plumbing and electrical. My question, sorry for the lengthy post, is: The paper backing on the insulation, should it stay on or be removed on the layer that would be directly against the outer wall? What I mean is, the paper faces the heated area but needs to be covered per code, per installation instructions… If I have one layer of insulation on the outside wall, then the water pipes and electrical wire, then insulation. Perhaps I am overthinking. I apologize. I am new to old homes. Thanks.

    1. Hey Brian, what you want to do is put one layer of unfaced insulation between the exterior wall and the plumbing and then one layer of faced insulation with the paper on the drywall side of the wall.

  19. What can i do to insulate my walls in my house. My house was built in the 1950s and has a cynder block walls with maybe 2″ space with plaster walls. How can i insulate my walls?

    1. Jeffrey, there are foam companies that can potentially pour foam into the voids in the concrete block if your block house wasn’t filled with mortar fire n the voids. Other than that your other options are to pull the plaster down and insulate with maybe a rigid foam board before putting the plaster walls back up, but that’s a real mess and expense.

  20. My son just bought a house built in 1935, he pulled up the carpet and the original wood floors are still there. However, you can see through the floors and see the crawlspace underneath. I have read if he insulates them then he can cause them to rot. Can he and how should he go about doing it?

  21. Can you apply clear sealant to sand rock houses to help with moisture absorption . I am sure it would be very expensive………………just wondering

  22. We just bought an 1820 Federal in Maine. We want to insulate and finish the attic for storage and a playroom. There is no ridge vent or soffit vents. Can I insulate without these and air channels running between the rafters? Can I use fiberglass or do I have to go with closed cell spray foam. We will be putting up tongue and groove pine car siding in the walls over the insulation.

  23. Hi, we just bough a house in Massachusetts built in 1895. There is a program run by the state (mass save) that covers most of the insulation costs. However, I was reading another blog ( and got very worried about applying insulation since the old houses are not wrapped in that thick plastic to prevent the condensation to get into the walls. The other blogger says the insulation material will attract moisture and will create mold and attract termites. What are your thoughts on that? We want to make it right. Thanks! Sam

    1. Sam, Bob is correct that this can cause problems depending on conditions of the house and local climate. This method is NOT something that everyone should use, but likely one of many possibilities to increase the energy efficiency. When in doubt don’t insulate like this, but if the conditions are right I want folks to know that it can work.

      1. Scott, thanks a lot for your reply. Would you mind expanding on what you mean by “right conditions”. We have back plaster walls that have no insulation and we are now debating what to do. Thanks for your advice.

  24. Hi Scott, we need to insulate and we have plaster walls, however our exterior is brick. Is there any way of blowing the insulation in from inside? Any other options? We don’t want to pull the walls down! Thank you!

    1. Mary Lou, insulation can be blown in through 3-4″ holes cut into the plaster walls and then the holes would be patched. This is a common practice for some insulation contractors retrofitting an old house. I’d look around for an insulation contractor in your area that can do this kind of work.

  25. The advice presented is pragmatic and wise, but I personally would not recommend insulating walls of historic houses in most climates at all unless there is some other pressing reason to open the walls. Instead, go into the attic, and check to see if the top of the walls are open into the attic airspace. If so, the wall cavities are acting like chimneys essentially. Plug the holes there to stop the air movement using foam, insulation board, or insulation plugs stuffed in a plastic bag. This prevents the vertical air movement within the wall cavities. Then caulk walls, addressing air infiltration by diligently sealing as many cracks as possible in the siding, wall outlets, etc. This approach minimizes the potential for moisture accumulation in the walls, avoids the common exterior paint adhesion problems that often accompany retrofit insulation in wall cavities, and prevents the insulation from breaking the plaster keys and causing the interior plaster to fail. It is not uncommon when revisiting insulation packed walls several years later to find a soggy mess at the bottom of the wall cavities. Then take the savings and put that towards a plug for the chimney, and additional insulation for the attic…or that neat new tool you have had your eye on for six months.

    1. Thanks all,
      I think my plan is to use HydroGap on the outside walls under the shingles, my understanding is it will prevent air flow but not trap moisture, and it has the rain guard incorporated;
      and to block the wall space in the basement (now) and attic (when spring comes)- (and look into insulating the attic as well)
      various things are mentioned to plug the opening to the wall space at top and bottom,
      should it be something that is vapor permeable like loose rock wool, or does it not matter, or would you use spray foam or something that really seals it?
      And, last, I have seen advertised a paint additive that is comprised of ceramic microspheres (“NASA technology” they say) that supposedly adds a measurable insulation value to the otherwise thin and useless (for insulation purposes) paint layer. Anybody ever try the stuff or know someone who did?

  26. Insulating old houses, especially complicated Queen Anne homes, is tricky, and preservationists and contractors will differ. You are taking a conservative, time-tested approach that will insure airflow to the siding and will all moisture to escape from the wall cavity.

    It may be possible to use some sort of housewrap or even a thin insulating board, but then you should have a rain guard–basically an airgap that allows water to drain off–to prevent moisture build up behind the siding. Adding thickness creates other problems with complex moldings, and changing the relationship of the window and door casings to the siding–they should always protrude.

    Blowing in insulation is not recommended–there may be knob and tube wiring lurking in the walls someplace, and it is not always easy to tell where, and moisture finds a way to get in and can cause mold and rot, especially near the sill.

    The biggest bang for the insulating buck is to insulate the roof. Balloon framing and complex roof profiles make this more difficult, but sealing the top plate and cracks and vents with foam and caulk (perhaps using the fireproof stuff for extra security) and using loose fill on the attic floor, will help. Insulating the sill and adding insulation between floor joists by the exterior wall (a tricky job, but if you are redoing siding anyway, do it then) will keep cold air from coming up from the basement and circulating around the entire house, including underneath every floor. Rock wool is a possibility for this because it is easy to install and is naturally mold and fire resistant. Again, be careful not to cover over any knob and tube wiring, which must have an air gap.

    If you can carefully use some window and door foam near the windows, without obstructing the sash weight pocket, that can do a lot to cut down on drafts, along with repairing glazing putty or even full window restoration to reset the glass and putty completely. Also check the drip caps and flashings, and caulk, although do not caulk under the window. Also make sure the routed drip edge under the sill is not full of paint and horizontal surfaces all slope 2-10 degrees to shed water. This will help prevent future deterioration.

    The Victorians used heavy curtains and blinds to cut down on drafts, especially at night, and heavy curtains in doorways, and only heated the rooms they used. These strategies still work :).

    1. Thanks, Kathy, for your thoughts.
      Scott made a comment at some point about HydroGap from Benjamin Obdyke, which I think I will start using, after exchanging some info with the company and getting a sample to touch and feel with my own hands. It includes a slight offset from the surface for enhanced drainage.
      Are you a professional, or filled with knowledge from your own home experience?

  27. Actually i was looking for this kind of information because in harsh winter insulation is only solution.I really like your effort of keeping all the details at one place.

  28. We are planning to insulate the unfinished attic of our 1927 bungalow in upstate NY. The contractor recommended that we install spray foam under the attic floor. The least expensive way to do this is to rip up the existing tongue and groove wood attic floor, spray in the foam, and replace the floor with plywood. The contractor said it would cost $2K more to save the existing wood floor and reinstall it after spraying in the foam. We’d love your thoughts on this. Thank you!

    1. Why not put the spray foam on the underside of the roof instead of the attic floor and keep the attic cool as well. I’ve done that in my own house with great success. You’ll likely get an insurance discount as well since certain foams act as a secondary water barrier. I’d leave the floor as it is and spray the roof decking. If you ever decide to finish the attic it’s already insulated.

      1. Thanks for your reply! A preservation architect told us that without major construction the attic ceiling height is too low for a legal room. He also wouldn’t recommend using foam insulation on an old house for a variety of reasons, though he acknowledged that many people love it. We were thinking that if we left the attic unfinished and used spray foam or cellulose on the roof decking, we’d be wasting oil to heat all that unused space above our living space. If we insulated under the attic floor instead, we’d keep the first floor warm and sometime later use denim insulation between the attic rafters to make the attic more pleasant for occasional use, but not for a full bedroom. So, we keep going round and round weighing all the options and can’t seem to decide how to proceed. We don’t want to do harm to our 1927 bungalow, but we don’t want to freeze all winter either. That’s why we were wondering about the wood on the attic floor. Thank you very much!

        1. Our house was built around 1900 and we did an energy audit. Our house leaked from everywhere, ducts, the attic, etc. We have a very low attic that cannot be used for much of anything. There are only three gable areas where a person may stand up fully. We had open cell foam sprayed on the attic roof decking without any problem. We could not use closed cell foam because the contractor said to use closed cell the person working the sprayer needed to be close (18 inches or less) to spray, so open cell (sprayer may be more than 18 inches away from surface being sprayed) was used in our attic. I cannot understand why the preservation specialist told you there were “a variety of reasons” not to use spray foam. A couple of days after the attic was foamed two electricians cut out all the knob & tube wiring and they re-wired our entire second floor and they were so thankful that we had the foam sprayed on the attic roof deck. It was hot the two days the electricians were re-wiring and the temperature was much lower than if we had not spray foamed the attic roof deck. One suggestion, if you need to do any re-wiring, do it before the attic is spray foamed. The foam makes it difficult for electricians to run wire on the outer walls down from the attic. We were a lesson learned for the electricians and spray foam contractors. After the electricians finished then we had all new duct work and a heat pump installed in the attic. Again, the HVAC technicians were thankful they we had spray foamed. Everything worked out in the end and our attic is over 20 degrees cooler since we had the attic deck spray foamed.

          1. Jim, my attic is the same way except with closed cell foam. Summer temps were about 130 before spray foam and are now they’re only about 10 degrees warmer than it is outside. And that’s only with 1 inch!

        2. I don’t think either option will be detrimental, but when it comes to insulating attics I always prefer to keep the extreme hot or cold out of the house by insulating the attic instead of the attic floor. Coming from Florida attics can get extremely hot in the summer. On a 95 degree day your attic could be 130+. So I would rather insulate against 95 degrees by insulating the underside of the decking tun try to insulate against 130 degrees on the attic floor. As long as you seal up any air infiltration on the attic floor you won’t be paying to heat or cool that space.

  29. I am impressed by your insulation knowledge. I have been in the insulation business for 26 years! Working in old homes is so fun and interesting. Thanks for all the tips!

  30. I can’t thank you enough for your site. In the process of removing all of the old dry wall, we found shiplap, then the vertical beams connecting it to the outside wood siding. From what I’ve read, there needs to be lots of airflow for my wood siding to breathe but then how do you insulate the interior walls and protect from water damage? Do I remove all of the interior shiplap, then put a water barrier (rain screen), then shiplap, insulation, new wall up? Many, many thanks.

  31. How do you insulate hard wood paneling walls that have separated. Someone had the bright idea to caulk and paint them. I don’t like it but too late now. It doesn’t look bad but I’m just curious what you do.

  32. We have a circa 1895 Queen Anne with the usual mix of cedar shingles and siding. Because of the overall poor condition, I am essentially taking it off (in sections), repairing/scraping what can be salvaged, and then putting it back on. Under the shingles/siding is generally a layer of decrepit rosin paper and then the wooden planks that are the outside skin of the house, often with gaps in between.
    Before now I have not blown any insulation in, nor have I used anything (like Tyvek) other than Rosen paper under the shingles, as I have been told that a house like mine was “built to breath” and one can make more problems with condensation and such if one tries to change anything.
    Any thoughts on what I’ve been told?

Leave a comment!

Keep the conversation going! Your email address will not be published.