How To: Insulate an Old House

By Scott Sidler • April 28, 2014


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.

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

  1. Great article. We bought a house in New Orleans built in 1910. We have plaster walls everywhere, but the upstairs is in total disrepair and needs to be completely gutted after years of neglect (windows that leaked etc). We are planning to spray foam the attic, but curious if when we remove all plaster/walls upstairs we should insulate the exterior cavity, add vapor barrier then drywall from inside of house upstairs? Downstairs will remain as is. I do not want to rip apart the outside of the house, but curious if I can do everything from the inside? and will this effect my downstairs situation at all? Thank you in advance.

  2. Scott, this article contradicts several points that I have seen made when researching insulation. Perhaps you could clarify for me your thinking on them.

    You recommend insulating at the roofline with batts, also at the attic floor, and leaving all of the vents clear. It was my understanding that if you insulate the roofline (ideally with foam, but batt if you must), that you never place any at the floor, especially if you don’t seal the space fully, as you will now introduce moisture into the floor batts. The only way around that I can see would be a vapor barrier on both sides of the floor batts, which I thought was also bad juju.

    My understanding was that you either use floor batts only, with good ventilation, or you seal the attic completely (again, with foam if possible) to bring it fully within the building conditioned envelope.

  3. You can simply insulate your antique house, however, below are some considerations which you must keep in mind. While insulating your attic make sure to seal off areas where you will be working with old insulation, caulk would be ideal for sealing off those spaces, and then remove old insulation and install the new cellulose insulation. Next install spray foam under your floor to stop any form of leak, or spider or bugs from getting inside the floor. Lastly, replace your old windows with custom storm windows, which would not only save costs but will also provide you with an unrestricted view. However, I would recommend you to use services of professional insulation service providers like Hire Custom, as they will suggest the best insulation materials suitable for your home, and that too well under your budget.

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  5. Hi, Many old houses have a complain and health issue. In old houses need External Wall Insulation and underfloor insulation. Because of weather effects, we need both insulation to protect our house and health. Without insulation we get more energy bills.

    1. You can’t generalize insulation requirements. Adding insulation to the walls of an old home in the south will lead to rot and mold and failing exterior paint.

  6. Hi – sorry for the length below.. need some guidance on an old house roof/insulation issue.. some context before my questions: I have a 1947 home in Florida with an almost no slope roof that has no attic and has no ceiling insulation. It’s so charming b/c the exposed beams inside have never been covered, but as you can imagine, it’s hot as h-e-double hockey sticks in the dead of summer. I bought late last summer and have enjoyed winter, but am working now with a roofer on an insulation-focused re-roof for this coming summer to keep it cool. i’m currently leaning toward a 4 inch insulation (R-25 current code for new builds) on top of the current roof and then essentially re-roof the very top of that cake, either traditional sheathing or the hydro stop approach. I can also choose to add a reflective coating.

    So, My questions: 1) will this general approach really lead to significantly lower inside temps? I have to assume yes since the ceiling temp in summer was reading over 130 degrees, basically baking the house.. new A/C couldn’t keep up. 2) will the exterior approach work as well as if i were to create a crawlspace by putting insulation in the beams and making a new inside ceiling? I really DON”T want to do this but I must solve the temp issue 3) is hydro stop worth it? 4) should i get the reflective coating no matter what?

    THANK YOU in advance 🙂

  7. Hi Scott,

    Last year my wife and I bought a large Victorian home Joplin, Missouri. The house is three stories with the third floor being maid’s quarters at one time. The home has been well restored on the first two levels by the last homeowner, and the third was scheduled for completion before he fell ill and unfortunately he passed.

    I’m looking at what still needs to be done and I have noticed that I have no insulation between floor joists behind my attic knee walls on the third floor. What I’ve been researching says that I should seal up the gaps between floor joists of the third floor right below the knee walls, and then blow cellulose between the joists and install soffit/eaves vents behind those third floor attic knee walls. What I am TEMPTED to do, though, is to just forgo the sealing up between the joists, and just blow cellulose between ALL the floor joists between the 2nd and third floor. The 2nd floor has an air handler which branches to dampeners in the floor of the third floor, so there would be heat that got up there. But things that I have read online have told me that I should avoid insulating between floors.

    Did this make sense? The previous home owner was doing such an excellent job with this house. I want to continue the good work that he started, and give the house the new life it deserves. Your input would be much appreciated.

    1. Yes, I know Bob and he is right on this topic. Though there is a place for everything and while this technique may work in only a very few situations it is still something that I feel should be out there for people to see.

      1. I highly recommend that you add a footnote to your article or rewrite it stating this… it’s misleading for anyone who is not reading through your readers comments and your replies.

    2. I just read another article by Bob who adamantly stressed NOT blowing cellulose into old Un insulated walls. He noted moisture aND rot problems. Bob I doubt you read this but which one is it? In an old balloon framed home should you blow in insulation or not?

      1. Graham, I know the article well and I agree with Bob’s points too. There are not a lot of times when this technique will work but on a rare occasion it may. For safety sake I would err on the side of causation and avoid blowing insulation into the walls unless you are absolutely certain.

  8. Hi there, I bought a house built in 1950, rancher with a crawl space. Outside is stucco with a few cracks in it and not really sealed on the corners. I took the drywall off and the batt insulation was black. Should I leave the insulation out and use backer board on the walks, or should I add rigid insulation to the inside of stucco? Thanks!

  9. My condo’s master bedroom has three exposed walls with no insulation. Walls are made of cement blocks covered with plaster and lath. Lath is attached to the cement blocks with 1×2 in. furring strips, so I can’t blow insulation. Can I attach rigid foam over existing plaster walls (FOAMULAR 1-1/2 in. x 2 ft. x 8 ft. R-7.5 InsulPink Furring Lap Insulation Sheathing) and cover it with drywall? I don’t have enough space to attach a 2x4in. frame (it is a small bedroom).

    1. There are angled braces in the walls between two by fours wall sections how do I get the entire wall insulated in each wall section without drilliing extra holes in the walls of the house?

  10. 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?

  11. 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.

  12. 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.

      1. Hi Scott. Can you clarify “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”? Do you no longer recommend blown in insulation for walls? What is the alternative process and material? Or if the moisture intrusion you are referring to is from vapor transfer from INTERIOR, are you recommending only insulating when you actually do remove the plaster and add a moisture barrier?

        1. Teresa, there are only a few cases where blowing insulation into the cavities works well. Usually only very warm climates with a good building wrap on the exterior is the only way it works without big modifications.

  13. 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.

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