Insulation is a crucial component in heating and cooling efficiency, helping keep warm air inside during winter and preventing hot air from entering during summer. Many homes built before World War II have been retrofitted with new sheathing, siding, and wall insulation. There are two types of solid wall insulation: internal insulation (cheaper option) and external insulation (more expensive but better performing).
A retrofitted wall assembly includes foam board insulation fastened to WRB-covered walls. The principle is to build up thick insulation (200-300mm) in stable layers, with an extra focus on cold bridging details at the slab perimeters, which integrate almost seamlessly with the external wall. Rigid foam boards, made from materials like extruded polystyrene (XPS) or polyisocyanurate, are effective for insulating exterior walls and foundations. They have high R-value per inch and are moisture-resistant.
To install insulation, locate underground utilities, excavate the foundation perimeter, and install a footing perimeter drain pipe to provide adequate exterior drainage. The best job has been where foundation stones are exposed, coated with closed cell spray foam, and covered with Thoroseal. The primary focus is to reduce energy use by 30 to 50, with emphasis on existing homes.
To implement a solid vaper barrier, choose a non porous insulating substrait, such as closed cell foam insulation. Cover the entire exposed area of the foundation and extend the insulation at least 18 inches into the ground. The current strategy is to tear the plaster and lathe off and install R15 kraft-faced batts.
📹 Insulating an old house: What to do!
Brent shows us the progress on the Kell house in Wichita Falls. A great turn-of-the-century home that is being restored. Brent’s …
Can you insulate a foundation from the outside?
Insulation is a crucial component of building systems, but it is often overlooked. It is essential to protect insulation from bugs and critters, as it works well on the outside of slab, basement, and crawl space foundations. However, insulation should not become an insect “interstate” and a home for critters. There are various insulation systems available, including extruded polystyrene, expanded polystyrene, mineral wool, rigid fiberglass, spray polyurethane foam, polyisocyanurate, and wood fiber.
To protect insulation, it is essential to drain water away from the building perimeter, gutters, downspouts, and other sources of water. Avoid making surface water into groundwater beside your building and send the water to your neighbor’s property. This will help prevent the insulation from becoming an insect “interstate” and a home for critters.
How do you insulate old foundation walls?
This guide provides a step-by-step guide on installing basement insulation. It involves choosing 2-foot-wide by 8-foot-high, 2-inch thick polystyrene insulation panels with tongue-and-groove joints, applying foam board adhesive to the rear, and pressing the panels against the wall. The process takes about 2 to 4 hours. Insulating your basement can lower energy bills, provide more comfort, regulate temperature, and address moisture concerns. This Old House expert, Tom Silva, will guide you through the process.
Can you insulate exterior walls without removing drywall?
Insulating exterior walls can be done without removing the siding by cutting holes in the studs and spraying foam or cellulose into the holes. This process can be done by replacing the cutouts, filling the holes with wood filler, sanding smooth, and painting the siding.
Basement walls can be insulated using foam board, spray foam, blown-in, or spray foam insulation. For finished basements with sheetrock insulation, contractors use similar methods to retrofit exterior wall insulation installation. Holes are cut for insulation installation, then patched and painted over.
Additional insulation can be added to attics, under the roof, or loose fill insulation like fiberglass beads, cellulose, or rock wool. Loose fill insulation should be added between 7 to 12 inches, meeting the requirement for older homes.
How do you insulate an existing concrete slab foundation?
Insulating an existing concrete pad typically involves a vapor barrier, foam insulation, special insulation tape, and a new subfloor. Concrete pads in garages are typically designed to slope towards the garage door, which is a building code requirement to prevent water damage. If the garage is used as a living space, the slant can be adjusted using self-leveling floor compound, a thin cement product with chemicals to bond to the existing concrete and prevent a “cold joint”. This step is crucial for a cost-effective and successful project. Some builders use self-leveling floor compound to correct the awkward slant and ensure the project is cost-effective and successful.
How to insulate the outside of a concrete block house?
Bill Wichers suggests that insulating the exterior using rigid foam, at least 2 inches of polyiso, is better than framing a regular stud wall on the interior. This insulation can be placed over exterior cladding or furring strips. On the inside, 2x3s can be used to create vertical channels for wiring, and standard 4-in.-square 1-1/2-in.-deep boxes can be mounted. This approach can help improve energy efficiency and reduce the need for stud walls.
How do you insulate an old concrete house?
Insulating concrete block walls can be done using various materials such as spray foam insulation, injection foam insulation, polystyrene beads, foam boards, and loose-fill masonry insulation. The choice depends on whether the walls will be covered or exposed, such as in a remodel or new build. Spray foam insulation is recommended before drywall is installed and studs are furred out, allowing the foam insulation to get behind the studs to prevent thermal bridging.
Can you insulate exterior walls from outside?
Blonded-in cellulose and injection foam insulation can be installed in an exterior wall of a residential building without the necessity of removing the interior drywall. This option is optimal for those who prefer not to undergo a comprehensive home renovation, as it permits the incorporation of insulation without inflicting substantial structural impairment.
What do you put on the outside of a foundation?
To prevent moisture damage to your foundation walls, apply a waterproof membrane to the outside of your home’s foundation after repairing and prepping the surface. This membrane can be a liquid-applied coating, a sheet membrane, dimple board, or a combination of the three. Concrete is porous, and when wet soil is pressed against the foundation walls, it absorbs moisture, causing moisture issues on the inside of the basement. A liquid-applied waterproofing membrane creates a barrier between the soil and concrete, preventing moisture-related damage.
Do I need a vapor barrier on exterior wall insulation?
Building codes mandate the use of vapor barriers with insulation to improve indoor environmental quality and energy efficiency. Building scientists recommend this method, as it protects against diffusion. Polyguard recommends a quality air barrier system to limit infiltration, exfiltration, and moisture accumulation in the building envelope. Contact Polyguard professionals for more information on when to use a vapor barrier with insulation.
How to insulate the exterior walls of an old house?
To insulate walls in an old house, apply a house wrap/vapor barrier, attach 1-inch foam board insulation, install siding, replace old windows with energy-efficient units, caulk window trim, and use weatherstripping to reduce air leaks. Before inscribing, learn how to safely insulate different parts of an old home, including the attic and roof. The average home loses about a quarter of its heat through the roof, so sealing the attic is a safe first step to retaining heat and saving energy. Sealing basements and crawl spaces is also essential.
Can you add insulation to existing exterior walls?
Insulating the exterior of an old house can improve energy efficiency without disturbing interior finishes. This method creates a continuous insulation layer, reducing thermal bridging through wall studs. When replacing siding, it’s an ideal time to add insulation. To do so, remove existing siding, assess sheathing condition, install a weather-resistant barrier, apply rigid foam insulation boards, seal seams and edges, install furring strips to create a drainage plane, and apply new siding over the furring strips.
📹 A Complete Guide To Insulating an Old Home (For COLD CLIMATES)
We will discuss how to insulate an old home in a cold climate using an old New England Cottage for the demonstration.
This is wonderful. I’ve worked on historic homes for 18 years. I have had really bad experience with spray foam. I’ve never done it but I always got the calls about mildew and windows “leaking” but it was always the spray foam that caused the problem and I had to remove it, repair and go back with more friendly and compatible materials and problem was solved. I love this article because it’s reassuring and does make me feel better in a weird way for taking all the hate for years when I spoke against it. Building envelop design is very important and love these websites! Thank you for posting this article
This info is saving our 1938 house right now! (It’s built more like those 1800’s homes, however, with no tar layer). Our contractor was so close to ripping out all of our historic lath and plaster and blowing in cellulose. Just thinking if we hadn’t done our research, it’s likely we could’ve lost our old growth cedar and fir home. We instead are so lucky to have found your website and have the language to communicate why we need to insulate the attic and basement only. Thank you for your expertise and clarity on these issues!
Don’t sacrifice the long term integrity of a home for short term comfort! – this is spot on. Working exclusively on 100+ year old houses in Philadelphia I have definitely seen what you describe. So called improvements have frequently been the cause of permanent damage and loss of historic homes. So much construction info on YouTube focuses only on newer homes and much needs to be thought through critically before applying to an older home. Great to hear from someone who understands and appreciates what we have in these homes. They are a treasure! Thanks Brent!
This is SO INCREDIBLY HELPFUL for those of us who own or have family with old houses! Also I am definitely an anti-foamer in mosts situations, because the application is super bad for the environment unfortunately. I do think it makes sense in unusually shaped buildings that would be super tricky to both seal and cut soft or rigid insulation for- like my dad’s geodesic dome outbuilding that he really should have insulated (a 1970s or 1980s kit, it’s a very large shed). Rockwool is really sustainable, it doesn’t burn easily, it’s affordable, easy for DIY builders to us, and you think it’s effective? Sounds ideal.
Can you talk more about insulating the 1870’s ceiling using rockwool? Is the roof currently vented, and if not are you planning on venting? I have an 1850’s unvented Philly rowhouse . Trying to figure how to insulate my cathedral ceiling and it seems like the only way is to add rigid to the exterior (if I’m to avoid closed cell spray foam)
What would you recommend for basement cripple walls or crawlspace walls in an older home? We have an 1895 house (PNW climate) and have been advised to do sprayfoam. The exterior of those walls is cedar shingles. I’m concerned about adding a vapour barrier where there wasn’t one before, but everyone seems to recommend spray foam in order to seal the crawlspace and prevent moisture from getting in
Love the article. would like some guidance. On our house 1878 Martinsville indiana. Currently has three layers of wood siding problem for us is we live in the woods and the red headed wood peckers love to put holes in the siding so we plan to metal putting siding on after removing all three layers of different aged siding and applying a Georgia pacific weather resistant osb. Then putting polyiso rigid foam on the outside of the osb. Inside the house has drywall with faux wood panels covering that so no real historical value. Would you advise the plan of the osb and rigid foam? We do use central air and heat with wood in the winter.
So true! I also follow UK websites. There was a movement in the 80s to “waterproof” historic buildings in England. Out with the old high-maintenance cob and timber, in with the new waterproof pebble dash. To their horror, the Brtits discovered that the “waterproofing” merely trapped water inside the structure. Fabulous old buildings that had survived perfectly sound for hundreds of years – rotted away in less than 10 years! Now there is a huge movement to return historic materials to historic buildings – even Georgian homes with completely modern style inside (no original architectural features) are changing from “modern” plastics to traditional materials for longevity. This is some GREAT content! I maintain that clay and lime plasters (both traditional interior finishes) are brilliant for moderating humidity. I have been informed (by Corbin Lunsford and Matt Risinger, no less) that I am delusional. Lime plaster walls are NOT cooler in the summer and warmer in the winter. Clay plaster walls do not absorb and release humidity, thus tempering humidity. I’m a nut job for thinking that the plastering and ventilating techniques first developed before the days of Ancient Egypt (and in continuous use in the Middle East ever since) is completely pointless. To achieve moisture control you HAVE to use plastic barriers and expensive high-cost, high-maintenance equipment. Sigh. Keep hammering away with REAL scientific evidence and maybe we’ll make a dent in the “plastic and foam is the solution for every building challenge” crowd!
Very well said. We worked on some older houses in the 1980’s. My Dad and some of the other carpenters said what you were saying “let the wood breath”. insulation experts would say something different to sell the insulation. Yet 15 years later those houses had some to a lot of rotting wood. As a carpenter I learned to lesson to my Dad.
I’m in Canada. My home is 3 layers of brick, no air gap, with the interior plaster being directly on the brick. So there is little opportunity beyond the roof and foundation for insulation. However, I’ve seen some fairy old retrofits and they seem to be good as long as the roofing and flashing has integrity. I’m going to suggest that foam would be fine in a wood cavity wall as long as there is an exterior air gap (possibly created within the stud cavity before foaming), much like a modern rain screen. Up here, the ability to insulate is the only thing that guarantees these houses remain, especially with the environmental laws coming and the cost of fuel.
I have an 1868 stone home in northern Utah that I will be remodeling. The stone walls are 18inces thick with added 2×4 walls to the interior for electrical and plumbing. How would you insulate that? my plan was to use closed cell between the interior side of the stone and the firring…but any suggestions are greatly appreciated!
Yeah when using closed cell foam there is 0 room for error. It’s the best for insulation reasons but if there’s an issue, and you don’t find it… water will rot everything. That’s why I’m doing closed cell on my basement walls, nothing to rot and there shouldn’t be an issue anyways. Rockwool is one of my favorites, especially for noise!
This is great information for anyone thinking of insulating thier historical home. I own a 1882 double brick home and was faced with this as well, we had an energy audit contractor come in while I was renovating my home and he strongly advised to foam it. I told him to take a hike… Alot of these experts have no clue. I built my interior walls 3/4 of an inch off the brick. Essentially creating a double brick veneer, then insulated with rock wool. These old places need to breath! As a carpenter I’ve seen alot of hack jobs ruin beautiful old homes. I’m so glad to see information like this posted.
My house was built in 1859 in Texas and I have 4 closets/attic spaces along the 2nd floor exterior front of the house and all of those closets are very hot in the summer. The 2nd floor air conditioning unit cannot keep up, I think, due to the cold air loss in the summer. I’m not sure what to do about these spaces to insulate. Any suggestions?
Hi, Brent. I am curious what would be the issue with using closed cell spray foam with the brick/stone 1938 house. If there is an air gap between the brick and sheathing to allow moisture to dry out and you are okay with Rockwool insulation, then why would closed cell spray foam (if sprayed correctly) be a bad choice?
I have a 93 year old house. it was built in 1930. I have been experiencing condensation inside my bedroom closet wall. I now have mold there. I was told I need air flow in the closet . Can I restore the wall and put a moisture and mold barrier drywall or should I use regular dry wall and take the closet doors off to make sure I have better circulation.. This house is old and does not have insulation inside the walls. Please help, I’m desperate.
So with a house built in the 1700s and not having to worry about paint chipping off since i have vinyl siding. Would it matter on the gap still? Also, would spray foam be a bad choice? I would be using open cell as well. Or would rock wool but fine. Currently redoing a bedroom in the 2nd floor and im running to an issue regarding insulation. Hence the question. Just wondering if open cell spray foam is the bad choice.
Brent, here we are in Deep East Texas, moved into a 430-ish sq ft, shotgun house with a windowed sleeping porch built on the east side. Drop siding outside. Hardwood floor. Sheetrock inside. Maybe…beadboard under sheetrock. 🤷♀️ Sitting on blocks about 18-24″ high. 18 wood frame, single pane windows: avg. 3 ea. room, 9 on that sleeping porch. My dad insulated the ceiling but there is no insulation in the walls. We figure the house to be 100-ish yrs old. Window unit AC. Small, soapstone, wood heater for heat. Over the hottest part of the summer I found the house to consistently stay 15°-20° cooler than outside without AC. However, I was worried about winter. …there was no need. We’re finding this grand, little house to be quite easy to keep warm! I just woke and built up the fire. Here in the kitchen it’s 56°…it’s 31° outside. In an hour or so it will be a toasty 70° here in the kitchen and 80°-85°on the sleeping porch where the heater sits. I’m translating my experience in historical sewing to old houses: we forget that people of long ago are just like us in that they liked to be comfortable, too. We just aren’t knowledgeable or comfortable with their ways of being comfortable. Back in the day, a wood stove would have been in this kitchen. (And there will be one here again…soon! 😁) With a wood heater in the living area of the house, these houses would have heated quite well! …and this house does heat very nicely! We just need to know how to work WITH the house.
Okay, brave question from a complete knoob here: I watch all these articles and I can’t help but conclude that the biggest mistake in home construction is the first one: using wood. It may be cheap at the outset, but it’s porous, organic, & a mold magnet. People like me in 8b climate zones are expected to replace their shingle roofs every ~15 years, and raised-seam roofs every ~30-40 years. That’s crazy. What if instead (hear me out) we built our roofs with non-organic materials that are easy to clean mold off of? Yes, mold would tend to grow in any temp/humidity transition zone, so why not plan for it? What if we made our roofs like pre-fab greenhouses, 2-ply or 3-ply glass on a composite frame, with a retractable mold-resistant fabric for a sun shade? My mom’s house in New England had a slate roof that lasted more than 120 years. It was bomb-proof, and look what we’re doing now. We’ve got to re-think this. What am I missing here?
This is very enlightening. I have a home energy efficiency evaluation for my 1890 home coming up in January and was going to have them do “the works” since I get such a good rebate through the state program. I’m also going to finish my attic and was excited to get the roof insulated by them too. Now I’m second guessing that plan. Is there a safe rule of thumb when considering adding insulation to avoid problems?
Thanks Brent for informing the builders who are working on old houses.Old houses are not new houses. If an owner of an old house wants to make their house feel be like a new house, they need to sell it and move into a new house. I have seen many an old house ruined by insensitive remuddeling. Tearing out original wood windows and installing smaller plastic “efficient” windows boils my blood. Sealing the wall cavities to prevent air flow is a … bad idea. Portland cement with old brick kills an old house. I’m spending hundreds of hours removing the work of informed “handyman” mistakes. I just subscribed. Thanks for saving our historic built environment. John in Bethel, Missouri
My 1930s Cape Cod had an attic that the previous owner had closed in, with insulation under the roof and in the walls. Down on the first floor there was a vinyl wall covering. When I peeled off the vinyl, I saw mold on the back side. The house was built so that there was an air gap behind the brick and block walls that went up into the attic. When the attic was closed in, that gap was sealed with insulation, leaving the moisture nowhere to go, blocked even from migrating into the living space by the vinyl. One step after another, innocently taken, had led to moisture traps in the walls that were now food for termites and other critters coming up from the crawl space.
I live in an 1870s house in the DC Metro region that is a similar situation to the 1881 example in your article. We are having some work done which involved the contractor opening part of an exterior wall and they say they have to install insulation to pass inspection. I asked for a dimple mat between the insulation and wood siding but they don’t seem interested. Should we remove the insulation after passing inspection or push for an air gap barrier like a dimple mat? What kind of dimple mat do you use? How can we best advocate for our old house?
Realy enjoyed this. My opinion is that you should think of the outside of the building as a rain screen. It will get wet with heavy rain and with driving rain it will get in and behind that surface. As good and as water tight as they make it. Nature will do its thing. So behind the rain screen should be a void/air gap at least 50mm which will allow any moisture water to flow. at the buttom of this 50mm gap there needs to be substaial venting to allow the material to dry. Then the next layer into the building can be wood/stone/brick. On the inside of that will go a breathable insulation like rockwool then it plasterboard/sheet rock. This gives you several things. Warmth of the building, Breathable inner wall. Water resistant outter wall with natural drying capability. This must sit ontop of a structure that is damp free or damp resistant which again is vented.
YES!!! You said “BREATHE” again! Steve (architect) Baczek & Friends from Build Science 101 need to watch this. They talk about how they “put to bed” the discussion of a house’s need to Breathe! They say it doesn’t need to breathe, “if it did, why don’t you leave your windows open?”?! What a ridiculous and unconvincing analogy! Thank you for “putting this to bed” at least for the logical thinkers…. 🙂 Spencer
I’m so thankful for this article Also!!❤. I have 120 year old farm house with Asbestos siding with tar paper underneath. She’s still standing strong and dry. But, i have been wanting to get the Asbestos off and replace with Exterior siding and some kind of insulation without ruining her ability to breathe.
It would be nice to see a period correct insulation material like eelgrass for that 1870 house 🙂 Eelgrass is rot and fire resistant (as it contains a lot of salts). Another period correct material might be buckwheat hulls . More modern material usable for filling 1870-cavities is “steam expanded cork” (grinded into granules) as it’s rot free and has good fire resistance. A natural material with great (future) potential is Typha Latifolia (and variants) as it has the same properties as eelgrass. I’m not a fan of cellulose as it’s not capillar active meaning it can not dry out by spreading the water but needs high enough tempertures so it can dry by evaporation.
Our house in S. Louisiana was built in 1935 and has no vapor barrier and no insulation. It has 7/8″ shiplap on the exterior and horizontal 1 x 12s on the interior. The interior walls were originally covered with a cheese cloth nailed to the wall and wallpaper on top of the cheese cloth. Later someone added paneling over the wallpaper. One room has sheetrock and it’s the best insulated room. From one of my remodeling projects, I removed one of the pieces of sheetrock and there was no mold or rot. We ripped out the bathroom to wall studs and floor joists and found no mold or rot. So, I guess that as long as the area between the studs are clear, air movement prevents mold and rot. I’ve noticed that some folks have covered up their exterior wood siding with Tyvek, insulated the walls from the interior and covered the Tyvek with aluminum siding. Others have ripped off the exterior siding, installed a vapor barrier and insulation, planed the exterior wood siding and the reinstalled it. I’m going to stick with sheetrock over the interior wood walls.
This is reminding me of when contractors would use portland cement in basements or even when repointing brick facades in historic homes instead of the proper lime mortar that was indicative of construction for the time period (since homes back then were built with a more breathable membrane since there wasn’t air conditioning). Part of it coming down to some not knowing the difference, and a majority of the time some builders just doing it out of sheer convenience, since lime mortar is not as readily available in most home improvement stores.
in my 1916 house (Z6) instead of a dimple mat, i used .75″ strips tacked to the studs and cut 2″ EPS to fit the cavities (glued and then foamed in) to act as a weather barrier. I also had to fur out the walls further to add more mineral wool batt insulation to get me over R20 walls. Was a pain! might have to consider the dimple mat approach. Thank you
Is this the same in South East Vermont? 1865 Post and Beam 1 1/2 story Cape My Envelope from the outside is Asbestos Shingle, tar paper, wood clapboard, Full 2″x10″ Boards as the sheathing . How would you insulate this ? Upstairs bedroom ceiling is live edge sheathing boards, Cedar shingle and then Tin to the outside elements. How would you insulate that ceiling? I have the entire house gutted. Thank you for any info.
I can just hear all the insulation salesmen out there telling their potential clients you don’t know what you’re talking about, so their sales won’t take a dip. You are absolutely right, a house needs to breath. These airtight capsules builders are encouraged to create are bad for the structure and us. Old houses allowed some bit of fresh air in, which is good for the structure and the health of the occupants. Our indoor air is more polluted then in any other time in history. I don’t believe all the toxic vinyl siding used is good for longevity either. It allows for untold rot to take place that you don’t know is there until it’s too late, especially when it’s place over our inferior modern wood products. Great article.
Thanks for sharing your wisdom, Brent. I have an 1890 Victorian in just the shape that you mentioned with 1888 home. While I understand the dimple mat / Rockwool combination for the balloon framed walls, after the drywall is installed and flooring finished, what would be your recommendations for open attic and under floor insulation? I want to give the house as much longevity as possible while offering the most comfort that I possibly can! Thanks for all you do!
For the 1881 house with the dimple mat + Rockwool install, looks like those are 2×6 studs. Did you use regular Rockwool batts for 2×6 stud bays, or did you you have to trim the thickness of the batts or use a 2×4 batt so you didn’t compress the dimple mat? I have a similar situation in my house. Thank you for this excellent info and article as always!
Thank you Brent! While trying to preserve my 1832 house, there seems to be hardly any sources for how to do it right without ‘new construction’ solutions. I have to ask though, I am about to get spray foam under the floor in the crawlspace and wondering if I’m making a mistake doing so, I have a pier foundation so encapsulation is crazy $, that and it did have 6mil plastic down but water was pooling and it caused moisture damage that I’ve repaired now. Any information on that? Thank you!
Ugh. I’m pretty sure I screwed up. I live in a 1900 house in western NY. I have cedar shakes and plaster walls. I had a company blow in cellulose for all the exterior walls a couple years ago. It rains quite a bit out here. What should I do now? How would I know if I actually have a moisture issue? If I do, can this be fixed without residing or gutting the whole house?
What about a 1918 Stucco home with plaster walls inside? NONE of the house is insulated and the city where my parents live, destroyed the foundation of their historic home while excavating and building a new sewer. For MONTHS, the house was shaking and literally rolling back and forth. The city told them they won’t do anything because of the statute of limitations??? I call bullshit on that. Anyway, the house is freezing in the winter and some of the upstairs barely gets AC in summer. Can you tell us if we can still sue the city or what to do to fix this mess?
I have a 1918 home. Original siding I do not want to replace and interior walls downstairs are plaster and lathe. I’m leaving it as is. However, upstairs, I have taken down the interior walls back to the studs and the ceiling is open to the joists. New rood being installed soon. I will not insulate the walls upstairs based on your advice. But I do have a couple of questions. Is it ok to put insulation in the walls joist bays at floor level? Does this help or hurt? Before I put in insulation in the ceiling and then finish, is it ok to spray foam the very obvious cracks? What do I do around the windows? Can I use spray foam? Also, in the dormers there are obvious openings everywhere along the sides of the wood siding. Any harm caulking each board before finishing the walls with drywall? Thanks!!
I have a question for an expert! I’m in maine and have a very odd home (for this area). It’s a stucco exterior, concrete in color (I think it IS concrete…?) with rock/pebble dash. The home has no insulation aside from new blown in insulation in the attic. There’s no vapor barrier in the walls either. Just stucco on mesh on wood studs. My home was built in the 1920s. I’m worried that as I renovate the interior room by room over the course of the next few years and add fiberglass batting with a plastic vapor barrier, that the walls might not breathe and rot the wood. The interior lathe and plaster is being replaced with drywall. The exterior stucco is unpainted concrete style. It seems VERY porous and breathable, like a cinder block, but I’m still worried that I could trap moisture? My first order of business is to get rain water away from the walls of the house by use of gutters (we just got a new roof so I waited on this) to keep the base of the walls as dry as possible. I’m just wondering if I risk rotting the studs by adding insulation in the walls or if this concrete stucco is breathable enough for me to insulate without worrying about rot?
Hi Brent, I truly appreciate all the wisdom and knowledge you have for historic/ older homes. We have a 1926 home with exterior walls without insulation. We are in the process of completing tearing off the ugly vinyl siding that was put on and putting on new WRB as well as a rain screen (6mm). If this is done, would blowing in insulation be okay in this situation or would you still recommend not to insulate the exterior walls?
If anyone has any doubts about what Brent said in this article, look up Dr. Joseph Lstiburek at BSC and see what he’s written on this topic (tons of free information), and feel free to argue with someone who has his doctorate in building science. You basically can’t cheap out on insulating prewar homes/buildings or you’re guaranteed to have mold and rot problems. Yes you can insulate and air seal them to an extent but it takes a lot of knowledge, money, and work by an trustworthy contractor to end up with something that’s more energy efficient and not rotting out in 10 years.
What is the best way to figure out what type of walls you have? My upstairs appears to have Sheetrock covering original shiplap or other board. Not 100% sure I can only see it from a wall socket. I am pretty sure previous owner destroyed almost all historic relevance to the bottom floor. Also if we are doing repairs to the exterior siding is it possible to add the air barrier and blow in rock wool or cellulose? We are going to remove the aluminum siding that is over the original clapboard and assume there will be needed repairs.
Summary: If the inside walls are old and pretty, don’t insulate. If the walls are drywall, rip it out, dimple membrane the cavity to isolate the external sheathing and let it breathe, insulate with rock wool, and paint the new drywall an old-timey colour. I didn’t hear if the dimple membrane needed to be air sealed, since it is attached to the studs, which are exposed to the potentially wet sheathing. Caution, when lath and plaster is removed and replaced with drywall, you gotta wonder WHY. Why was it so bad that they didn’t repair the hole or crack? Why go through the huge, dusty, expensive process of replacing? Was it broken through neglect and abuse or are there structural issues causing the wall to deflect?
I’m curious – at 5:54 you’re talking about adding the dimple mat and creating an air barrier, if you wrap it around the studs as well is that creating an insulation problem since hot/cold air will flow directly to the drywall? Also curious if this solution would make sense in southern california where it’s hot and dry most of the time. Thanks for your articles they’ve been super helpful and a great resource!
You still did not address condensation buildup within the wall. I have a small Victorian, 2 br. After 2 years of research I decided to foam with 2 inches of closed cell foam facing the outer wall to stop condensation from forming and finish off with 2 inches of open cell facing the interior. If you don’t address this with your mineral wool/fiberglass/cellulose you’ll get mold. I’ll know in a couple of years if this was the correct way to go.
Homes are built different from region to region, your Texas 1880’s home may not have been built like one say in the NE states. A single solution approach can be dangerous form a health and safety standpoint along with durability. I agree on not using foam when you’re not the contractor putting on the exterior sheathing because it is not if you will have water issues just when and how long will it take to notice the problem once it has started. Retrofitting homes is a difficult job for even the most experienced contractor along with having the ability of explaining it to homeowners so they understand why or why not to insulate with certain products. I have more homeowners think I am not telling them the truth than I have had them go with our approach because so many contractors do not care about the longterm affects. I have made many mistakes but when we repair those we make sure to learn all we can for future projects. I will make more mistakes and continue to get better, if you don’t admit to yourself and staff you will get sued out of business. Good Luck out there!
So you’re talking about high density spray foam correct that has tight cells you don’t agree with even though it’s the rave right now of technology it’s been around for such a long time. But for these older houses, you are recommending against Spray Foam? So for floor joists on our house that was built in 1915 sitting on the foundation crawlspace underneath a new insulation in between the floor joist at all and no insulation in the roof rafters at all. Would you recommend blow in insulation into the attic and just put your common batting insulation under the floorboards For insulation? Thank you. 4:39 😮
My wife and I are purchasing a 1906 Farm house in Illinois and the siding is in such a bad state it will most likely need to be completely replaced. I understand not filling the walls with insulation especially since it still has plaster and lathe walls, but would using Zip R-9 sheathing with the strips for air gap Matt talks about under the wood siding be an acceptable solution?
I had old growth shingles with chipping lead paint on my garage walls. I got scared of the lead paint, and removed all the shingles. Silly me! I should have done lead paint removal instead and just repainted them. It was a forever product that would have lasted for another hundred years. Good thing I only stripped two sides of the garage in the back.
👏👏👏 great advice! In the UK most properties are +140 years old!🧐 Insurance companies here will NOT insure a home with blown cellulose or crap like that. So you can’t sell 🤷😬 It is causing damp, it is a catastrophic cheap way of isolating attics, the worse… everyone who did it start removing it! 🤯 before it’s too late. Better of using loft rolls, takes longer, more expensive but at least you can resale your property 😁
It would be great if you could do part 2 talking about how you handle basement/crawl space and attic insulation … and also sealing (caulking) around windows. I’m dealing with a 1910 brick row house with original windows, a 1920 stuccoed bungalow both with full basements, and an 1870s timber frame on pier and beam. Drafts are an issue all around.
We have a 1920s house, zone 5, with original wood siding that we’re exposing, felt underlayment, nailed to shiplap sheathing on 2×4 nominal studs, and original lath and plaster. We’re considering blowing dense pack cellulose into the walls through the sheathing side. Is this an assembly you’d feel confident insulating?
Brent: Just an observation. I live in New England and my family has an early 19th century home farmhouse that my father-in-law had cellulose insulation blown into in the late 1970s. It has held up very well. By no means would I consider it to be a “high performance home”. By and large, being a residence…not a museum, pool, spa…the humidity fluctuates with the seasons. Also, air conditioning is generally not used. Sheathing and siding are wood and there are decent overhangs that help shed bulk rainfall water….the region gets 50-plus inches per year. When we added a small addition in the 90s and removed siding in one area we were impressed to observe that the cellulose hadn’t settled and was nicely and tightly packed. Best of all if there is some short term water vapor (not bulk water” drive the whole assembly wood sheathing and insulation can absorb this as a buffer and dry out in both directions. One downside of a system like this may be that the exposure facing north, when insulated, tends to take a bit longer to dry out when exposed to heavy rainfall and is subject more freeze-thaw. This means it needs to be repainted a bit more often. In general, the paint finish on the siding in this region, especially at a higher altitude, just takes more of a beating and repainting plus selective bevel siding replacement is a fact of life and has been for centuries.
Why do you need the dimple mat if you’re using Rockwool which will not hold moisture but is vapor permeable ? If you use drywall and use a latex paint which allows the drywall to remain vapor permeable wouldn’t you wall be able to dry to both the inside and the outside ? Btw I am in climate zone 4/5 if that affects the answer
Thanks for the thoughtful articles Brent. I have a 100 year old brick home, two wythes of brick with furring strips and wood lath plaster walls. For the kitchen and bathrooms, I have stripped down to the brick, and it seems to me the safest option is to re-furr (is that a technical term?) the brick, and hang drywall. I was considering stapling Tyvek over the furring strips to provide some barrier to air movement, essentially establishing a 3/4 inch gap between the Tyvek/drywall and the brick. Any thoughts? Thanks!
My older home was built in the style of your first example; wood siding, airgap, and then beadboard. I’m not putting insulation in, but my question is for the inside. Can I put drywall over the beadboard, or do I need some type of vapor barrier first? When I bought the house, it sat empty for about 3 years with the doors open (kicked in from thieves), the drywall was dirty with some spots of mold. Should I replace the drywall the way it was-directly on the beadboard or use a moisture barrier then the drywall? The beadboard isn’t airtight, I’m concerned with the drywall getting wet, but then what type of vapor barrier should I use cause I’m afraid that will get moisture between the beadboard and the barrier causing the beadboard to rot. Thanks
My family owns a 200-plus year old farm-house in southern Vermont. Painted clapboards on solid wood sheathing and plaster interior. Quaint but architecturally unremarkable. We blew in cellulose in the late 1970s and it has performed very well. No vapor retarder anywhere in the assembly. Walls can dry in either direction. We removed a section of one wall 30 years ago to connect to an addition and the insulation was dry and there was absolutely no settlement whatsoever. Our addition was built to Code with a poly vapor barrier and fiberglass insulation and now there is considerable siding and OSB sheathing rot because, I believe, the siding/sheathing layer could not dry to the interior. Cellulose is great stuff and does function as a moisture sink. Nevertheless, a well insulated building will have cladding that takes longer to dry out in wet climates.
Great article, thanks. My 120 year old house has double brick outside walls. I have removed the plaster and lath and I am going to build a 2×4 wall about an inch off the brick and fill it with rockwool. There will be a vapour barrier on the inside, but I am not sure what to put on the outside between the insulation and the air gap. I want something that will hold the rockwool in place, but will also breathe so moisture doesn’t get trapped in the wall. Any thoughts?
I’m doing a major remodel of an 150 year old, large home in New England and we had to foam. There was just no other way to properly insulate the home. When it’s -10F outside and #2 heating oil is $5.75 a gal. Not insulting the walls is just not possible. You can’t have the floor 55 degrees and the ceiling (10 foot) 70 degrees with the furnace constantly running. I had mix feelings about the foam but with the wall cavity at 4 inches, there’s no other real solution other than closed cell. I think rock wool is over hyped. It’s just basically semi waterproof, but costs a lot more.
I have a question related to my current project. Please comment. I’m a first time DIYer and I have something similar to 1938, although mine is 1974. I’m in climate zone 3 (hot and moist) on the very edge of zone 4 (cold and moist). Slab foundation. Walls consist of: 3″ brick, air gap, particle board sheathing, 2×4 studs, R11 faced fiberglass insulation, wood paneling. I’ve stripped off the paneling and insulation. Although this house has taken on a lot of water, its in better shape than I expected with very little rot on the 2x4s and minimal mold. I have analysis paralysis! What to do about areas where there is no sheathing? How much sealing should I do? I do not want rot and mold but also don’t want discomfort and large recurring bills in order to make the climate comfortable. Problems. There is no house wrap so nothing to stop the wet brick from driving vapor into the house. The particle board sheathing appears to be impregnated with something but its crumblally and is missing in 10% of the wall bays do to water and rodents. I thought about spray foam in the cavities where there is no sheathing but I really don’t know what to do.
You will be hard pressed to do something better when our forefathers and elders, working with what they had, created things of lasting style and durability. They observed what worked and what didn’t, but they just didn’t write it down. We are not smarter than they are, so any attempt to do better requires us to think very, very carefully about the hows and whys of the era.
This is an excellent article! I have a quick question about a scenario that is very similar to your 3rd case. We are remodeling a 1920s house (remodeled in the 1950s) in Texas. The exterior is a concrete smear sprayed on the brick in the 1950s. Then there is an air gap followed by tar paper. Then we have shiplap, stud, and shiplap on the interior. The house has no insolation. An “expert” told us not to insulate unless we can re-do the exterior and put a Tyvek vapor barrier. He was worried that the new AC system will cause issues in this scenario unless we put in a propper vapor barrier. After perusal your article I now wonder if we can insulate because of the air gap. A true expert opinion would be great.
I think I may have found a website ill be referring back to quite a bit. We are lookong into purchasing a house built in 1904. It’s been partially restored, but it still has no attic insulation at all. There is a wooden floor up there, with nothing in it, and a very tall peak, about 14 feet from the floor to peak. Heating and cooling are my only concerns with it as it is quite large, 2779 sq/ft on the 1st and second floor with 10 foot ceilings, 9 foot ceilings in the full basement, and of course the full attic. Thats A LOT of cubic feet to heat/cool
Hello, 1915 N.E. home painted cedar shingles, w/lath and plaster walls, minimal insulation on attic floor only, nothing in walls. 2nd floor cold in winter, hot in summer. Finally removing knob and tube wiring so insulation hopefully is a option. I want to know what I should advocate for . Should I expect the insulation to be done through the interior or exterior walls? I am going thru a state energy program so want to ensureI I do the best for this Old House. Thanks!!
Adding my 2 cents: if you want to live in a really old house and have it looking like it did back then, it’s good to live like they did. When it’s really cold, don’t try to heat the whole place. Have zoned heat or wood or pellet stove where you can spend your time so kitchen living room etc and let the rest of the house get cold. Then the issues around modern level insulation don’t really apply.
Not sure if you’ll see this comment, but I’ve been trying to tackle insulating my old fixer-upper I got recently and it aligns most with the last house you mention here. I am running into an issue where I cannot confirm any sort of air gap behind the exterior brick. A couple places (in corners) I have observed the brick being just about touching the shiplap sheathing, and others there is an air gap about 1/2 inch wide. in one place the mortar has degraded somewhat and pieces have filled the gap near the wall’s base. How much of an air gap is needed for airflow behind the brick? should I err on the side of safety and put a dimple mat behind the shiplap anyway? Any thoughts or comments are appreciated. Great article! very informative and well thought out.
Brent, could you expand on insulating the floor system and benefits you may gain outside of an air barrier? Im in the process of purchasing my wife’s family farmhouse. Historic, 1880’s but built very well by her great, great grandparents. I’ve been in the business for 16 years but this house is going to be the biggest challenge I’ve taken on. I was considering tearing the plaster out of the exterior walls and insulating per room as I remodel but considering leaving them alone as they’ve been this way 140 years and no signs of serious rot anywhere. Would also love to hear your thoughts on shotcreeting the limestone foundation walls to minimize intrusion and add integrity. It’s also a much more cost effective solution then jacking the house and pouring new walls. Love the knowledge you’re sharing!
I own a 1935 house in the northeast. I got sick of the exterior maintenance and the energy use. Ripped all the siding off, installed vinyl shakes with a very realistic look (and wrapped everything), did 1.5″ of GPS foam board (for better breathability), with house wrap under it. Blown-in in the true 2×4 walls. Unknown how it’s going to hold up, but it looks great from the street, and it’s drastically reduced the energy bills. I know a lot of folks don’t care for doing this to an old house, but I don’t want to deal with painting for the rest of my years! Zero regrets so far and tons of compliments!
So many contractors and their crews are just product installers. I don’t think they consider what really has to go into the use of these products. So you have contractors deciding to use products without knowing the ramifications and then you have the installation crews who have no real understanding of what the product does or what it needs for correct installation. Sloppy installation of ill-considered products leads to disaster, sooner or later. Usually just “later” enough that the contractor can’t be found and only the owner is on the hook for fixing.
We’ve acquired an 1900’s home. Plaster walls, still mostly intact. Field stone outside walls. Were very unsure how to approach insulting. We’ve recently decided to focus only on insulating the attic. (Should we do both the floor and the roof in the attic?) But as the house was originally heated with a coal stove from the basement im very unsure about insulating the floor as the house has only a few vents in the upper most level to let the heat through. The middle floor has a huge grate right over top of the old coal furnace in the living and dinng room area. My husband and I are planning to use a indoor wood furnace and rely on heating the home the same way they originally did. With the heat radiating through the floor and eventually getting trapped by the good insulation layer in the attic. I am very worried about rotting our walls out if we dont air seal. And i really dont want to tear out the plaster. It has very minor issues. Small cracks in a couple corners. ….. are we nuts? 😂😂
When I turned 11, we moved to what, then was the middle no were. My parents purchased an old house built 1893. It had been sawn in half right down the middle and moved in the dark of the night. Reassembled, and thats it. We did a lot of starting over those first few years. Learning can be a slow process. Don’t give up keep working. It was so worth it.
Brent, we just found out our attic doesn’t have hardly any insulation. What should we put up there? Also, when the house was moved to a new foundation there is now a half inch gap on the east wall between the sill of the house and the foundation. My contractor suggested spray foam. Any other ideas or is it ok to use to fill that gap?
Thanks for that info . I live in New Jersey in a 110 year old house 0 insulation and a ballon frame construction. I want to insulate the rim joists in the basement, i was thinking about using spray foam or just rigid foam board and spray foam around the rigid foam. looks like rigid foam is the way to go.
The 1910 McClure, Greene&Greene era homes in Victoria, BC are the same. Some you could do something, others we left as is. The tar paper on the exterior was still in decent condition 100 years later. The wood in the homes….western red fir (now close to extinct) only continues to toughen into iron wood if allowed to breathe. Couldn’t put nails into it. It was worse than LVL’s. That said, those homes with proper gutters and basic maintenance will still be here 100 years from now. Can you say that with most spec homes today?
I have a clarifying question. On the second house that had plaster walls replaced with dry wall — I am assuming it still had lathe in place too? Or is that considered to be a barrier that can’t be penetrated like the breadboard? My house has no remaining plaster but I know there is likely lathe under the drywall, as the walls with no drywall show lathe.
I stuck a piece of foil up on the roof and calked it in. The roof looked good and I ddint see any sigh of leaks. It only took 1 yr for the small leak to rot a 4/8 section of the roof and beams. I removed the foil face and once it dried out I still couldnt find the leak and all other sections I didnt insulated were fine. Most builders dont understand the moisture side of building science.
Hi Brent! Thank you so much for the great information! I am currently in the process of rebuilding a home built in 1910 located in northern Florida. I am curious what you think about exterior painted wood. The old heart pine Dutch lap siding that was painted many years ago is peeling very badly all over. How would you go about refinishing this? Any tips would be greatly appreciated! Keep up the good work! I love learning from our past and making it better with a little building science!
I very much agree about spray foam insulation and foam insulation balls which were used in the UK for a little over a decade to fill the air gaps between masonry courses on preexisting buildings here. Causes serious moisture issues leading to damp, mould and rot in masonry and timber buildings some of which had previously stood for centuries with these sorts of problems. Curious, I don’t see much PIR board (foil backed, foam boards) used in the US. Any experience with them?
I renovated a 1904 house. The exterior siding was already replaced new 8inch textured aluminum. Under that is the original doubled up shiplap with plaster and wood lathe on the interior. When we were running new electrical, every exterior wall we opened up we found blow-in insulation. So at some point, I assume when the siding was done, someone filled up all the walls from the exterior previously. The first winter it sat vacant (keep in mine our winters are minus 30C in canada) I couldn’t believe how low the heating bills were for a house of this age but now I know why.
So glad I found your website. My plans are to build a simple one bedroom cabin 30 x 24, no loft. It will not have air conditioning and will be heated with wood. The most important thing to me is to enjoy and preserve the natural beauty of the rough hewn lumber exterior and interior. We will be using hemlock and hickory. In your export opinion, should we insulate ( rock wool) or not? My concern is will the untreated lumber be able to air dry if insulated. There are no building codes in my area and It will be off-grid. Thanks for any suggestions you may have.
This is important information. With old houses we need to think through how people lived when the house was built, and why certain things were done the same way for decades. I’ve seen/read about various homes from the 1800s where literal newspapers and Sears Catalogues were used inside the walls for insulation. Cellulose!
I appreciate this article. We have an 1894 house in northern Indiana with a similar situation to house #2 in the article. The interior plaster had to be removed, and all we are left with is wood clapboard (poplar) mounted directly unto 2×4 studs. We are really struggling to decide on what, if any, bulk water and air barrier to affix within the stud bays against the clapboard. In the article, Brent mentions simply putting dimple mat, Rockwool, and drywall up in this scenario. Does the dimple mat serve as a form of air and bulk water barrier? If so, do you tape it in or simply place it into the cavity? And since I’m in the north (building zone 5) where the relative humidity of the interior of the house from cooking, bathing, etc. can be greater than the outside humidity for 6-9 months of the year, I’m concerned that dimple mat won’t allow water vapor from the interior to pass through? Do you think this will be a problem? Thanks for any feedback or resources you can recommend.
Interesting. I have a 1870 20″ thick full stone house here in the Belgium Ardennes ( Battle of the Bulge area). I stripped one of the five bedrooms and to insulate it, i will use aerogel mats, bluetec. They are only 1 cm thick and do as much as 8cm rockwool. It will be glued with a breathing glue/plaster. This way, i hardly loose room because it is thin. The material is light, does not burn and breathes.
This is great. Love the attention to restoring old houses (in addition to the focus on high performance houses in many other articles). One question about case 2: The siding is directly on the studs without any sheathing, right? How would you approach this case with siding and old sheathing from rough sawn boards (no plywood, no vapor, moisture or air barrier)? Very common in New England. Is the dimple mat or air gap for drying in general still necessary? Many of these houses got blow-in insulation 40-50 years ago without air gap and without vapor barrier. That approach seems fine based on historical experience. So in this case, would you just put the Rockwool in the cavity without air gap and without vapor barrier?
First house was a 1913 craftsman 4 square in WA. No wall insulation and no rot. Only place I found an issue was a wall that had been opened up to change the windows. And so the city required they fill the cavities with insulation. Low and behold the sheathing boards on the outside had water damage and minor rot.
I’m in coastal Maine and have been pounding nails for 47 years. I have seen so many old houses, early 1800- 1940 more or less, that the paint is peeling, and the wood is rotting. Every one of them have been modernized with lots of insulation in the walls with no thought given to the fact that basements are wet, the foundations are granite blocks and in a lot of these houses’ ledge is exposed so you may have a river in the spring when the snow melts and in the summer from rain. If the back of the exterior walls can’t breathe and dry the paint won’t stick. Although I am too old to take on a big reno, I love your idea of the dimple board to allow airflow and I’ll pass it along.
Thank you for this information. We gutted our 1912 two story house last year. I installed lathe vertically in all the exposed 2×4 bays for an air gap. I then started fitting 2″ foam in all the bays, then 1″ foam with their perimeters all sealed with spray foam. I am now going to put poly vapour barrier and then another 1.5″ of foam before the drywall. This will give us R27 walls.
I’m doing a full-gut renovation of a 1920 house, and this article makes me feel like I’m on the right track. Using rock wool and maintaining a 1/2″ air gap between the insulation and sheathing is the strategy I’ve decided on after a lot of thought and research. I’m furring out the studs to match the thickness of the original plaster, so as long as I don’t push the 3.5″ rock wool all the way back against the sheathing, I find that the dimple board is unnecessary for me.
I recently bought an 1890 multifamily. The firs floor has cedar shingles the other 2 have asbestos. the first floor shingles have peeling paint and it has blown in insulation. I figured it was a bad paint job but this article is making me wonder if the insulation has something to do with it. Is there anyway I can diagnose this so im prepared moving forward?