bloglovinBloglovin iconCombined ShapeCreated with Sketch. Fill 1Created with Sketch. Fill 1Created with Sketch. Fill 1Created with Sketch. Fill 1Created with Sketch. Fill 1Created with Sketch. rssRSS iconsoundcloudSoundCloud iconFill 1Created with Sketch. Fill 1Created with Sketch. Fill 1Created with Sketch. Fill 1Created with Sketch. SearchCreated with Lunacy Search iconCreated with Sketch.

How To: Insulate an Old House

How To: Insulate an Old HouseI 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.

What’s Your Climate?

Your insulation plans should revolve around your climate. After all, you wouldn’t insulate a house in Miami the same as a house in Michigan. I’ve written two detailed posts about how to properly insulate in either a hot or cold which might be a good place to check after getting the basics in this post. Check them out below.

Insulation For a Hot Climate

Insulation For a Cold Climate

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. Should it be done? That is another question.

Adding insulation to the walls of an old house without any other precautions can result is rotting walls full of mold under certain circumstances. In other cases, drilling holes in the walls or removing a couple courses of clapboard to blow insulation into the stud bays may work with no problems.

The problem is that it is difficult to know which situation you have, and so it’s usually best to leave well enough alone and not insulate the walls. The bigger paybacks are under the floor and in the attic anyway.

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.

Subscribe Now For Your FREE eBook!

88 thoughts on “How To: Insulate an Old House

  1. 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

  2. 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?

  3. 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?

  4. 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.

  5. 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.

  6. 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?

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

  8. 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.

  9. 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.

  10. 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.

  11. 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?

  12. 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?

  13. 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.

  14. I find that your steps in insulating an old house are efficient and simple. We know older homes were obviously built without insulation. This article provided great DIY steps that are easy to follow. Thanks.

    Insulation Services Adelaide At Tiptop Insulation

  15. 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.

  16. 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!

  17. 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.

  18. 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.

  19. 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 Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.