Should you insulate an old stone house?
Those beautiful old stone houses from the 1800s are a piece of our heritage that should be preserved, but in colder climates like Canada and the northern US States, wow - are they energy pigs! To bring an old stone house into the modern age of energy efficiency is not the easiest thing to do for a number of reasons, so the renovation techniques are very different from wooden homes of the 1900s and forward.
Here we will explore a few of the options for types of insulation, where to put that insulation, and even options without insulation but using super-efficient heating systems.
The efficiency problem with stone houses is the fact that there is little in the world that insulates less than stone does, so when the entire wall system of a home is just rocks and mortar, you are pretty much living in a modernized cave. Those stones will suck the heat from your house and radiate it to the exterior with great ease.
And since an uninsulated stone house is just rock on the inside and outside, the options for insulation involve completely altering either the interior or exterior. Neither of those options is very appealing, as you lose the heritage look either outside or inside, so right off the bat, the first consideration is – are you okay with that?
The second consideration is budget, since either inside or outside, it will take a lot of investment and work to bring it up to modern energy-efficiency standards. This is why many stone-house energy efficiency upgrades don’t involve any insulation at all, and instead just invest in super-efficient heating systems, like geothermal ground source heat pumps, or air source heat pumps.
First, we will explore the options of interior and exterior insulation and you will quickly see why skipping insulation altogether, as insane as it sounds at first, may make the most sense.
Insulating the interior of stone houses
Insulating an old stone house from the interior is probably the simplest option, but not necessarily the best for several reasons. From a quality-of-life perspective, you will lose interior space. And the better job you do, the thicker the walls will be so you lose even more space. Now there’s a double-edged sword if there ever was one.
To go to that much work and only minimally insulate your walls can be something of a wasted opportunity, and that is the problem. Your want decent insulation but need to balance it with reducing living space.
Insulating interior walls of raw stone would mean framing an interior wall, bringing wiring forward into the new wall, drywalling and painting. That in itself is not a small feat, until you compare it to insulating the exterior.
An important note before moving to the possibility of interior insulation is the fact that a stone wall that has likely been kept warm for 4 seasons since it was first built, will now be subjected to a seasonal freeze/thaw cycle. This is very similar to the problem of insulating a CMU concrete block basement in a cold climate that has a deep frost line. Not having any insulation is what has prevented the freeze-thaw cycle from causing issues like frost heave as the wall has stayed above freezing. With interior insulation fitted, that freeze thaw cycle can weaken mortar and lead to structural deterioration, so this is generally not a recommended solution for cold climates.
If this is really the way you feel you want to go, we would recommend enlisting the help of a structural engineer to determine if interior insulation is a safe option in your particular climate.
Insulating the exterior of stone houses
Exterior insulation of stone houses is the safest option for protecting structural integrity and for optimum energy performance. It encapsulates all the stone inside the building envelope, so along with protecting the mortar from freeze damage, you will reap the benefits of thermal mass for regulating home temperatures.
Other benefits come from the fact that old stone houses are often in rural areas without close adjacent houses like there are in urban areas. So there is less chance you'll have allowances and setbacks to respect that may project the exterior wall surface into close proximity with property lines. Meaning, you are often able to build thicker walls to improve the future performance without encroaching on neighbors. Or neighbours if you're Canadian, eh.
The downsides of renovations to add exterior insulation start with the fact that you longer have a stone exterior to your home. After that reality sinks in, other challenges include the fact that the roofline might not accommodate the thicker wall, nor will windows and doors. That means building out window and door frames to match the new wall, and of course it means money.
And at that point you need to look at the quality of your windows. Is it worth doing such an upgrade but not installing high performance windows as well? If a stone house has no insulation, dollars to doughnuts says the windows are pretty low-quality and likely need replacing as well.
One of the biggest hurdles you wil face when thickening exterior walls is how it will interface with your roof. A fairly common design feature with older homes was a very minimal roof overhang, so exterior insulation work (as you can see in the image below) may protrude past the existing roof and force you to into a much more extensive remodelling project.

Extending rooflines is not always a suitable option, so often times you are looking at building an entire roof on top of the existing roof. That means the entire exterior surface of your home – walls, windows, doors, roof…is all brand new. Is that what you wanted? I hope so, because you are likely well over a 100K and even closing in on 200k for a project like that, even for a relatively modest size home. So if you were undertaking this to save money be sure you actually will before you start.
Cost effectiveness of insulating old stone houses:
Improving the energy efficiency of any home is a noble move towards energy efficiency. But will you save money or end up spending way more? Let’s do the math and find out, only I have no idea how big your house is so you’ll need to fill in the numbers yourself. You first need to compare the current heating bills with the projected renovation costs, and find out if you even a chance to save money in the long run. Here is your price-sourcing homework:
1. How much insulation and what type
2. Insulation attachment method – Cascadia clips, Larsen trusses, or rigid foam panels
3. Furring strips, siding purchase and installation
4. Rebuilding roof – trusses, insulation, sheathing and roof covering
5. Purchasing and installing new doors and windows, or modifying existing ones
6. Energy modelling of that design to compare previous heat load to determine financial savings
After doing those calculations, you might find that your children have an outside chance to see a financial return in their lifetimes, just not you in yours. That is why the preferred method for reducing heating bills in old stone homes is often done simply by upgrading to super-efficient heating systems and leaving the walls and roof alone. Even so, there's one thing we didn't mention and that is the comfort factor - but that's in this other article.
I say that with one caveat – if there is no attic insulation it would be very much worthwhile to do that first before calculating heat loads and pricing systems. Attic insulation is a stand alone project and should be done regardless of other renos or heating system upgrades.
Important note though - insulating attics of old houses with minimal overhangs can go very wrong, so see here first about how to insulate an attic and have proper ventilation and also prepare yourself for ice dams on the edges of roofs that can back thawing water off the roof into your house!
Geothermal ground source heat pumps or air source heat pumps for old stone houses
By forgoing exterior or interior insulation and instead opting for high-efficiency heat sources such as heat pumps, you avoid a lot of headaches, including:
- Avoiding structural risks: No need to worry about compromising the stone or mortar integrity, walls will be as warm as they ever were, so there would be no additional degradation of mortar or structural strength.
- Lower upfront disruption: Installing a modern heating system requires far less construction than insulating. This can be done with very little upset to your living situation, and can usually be done in a matter of days, possibly use existing ductwork if there is any, or by choosing an air to water high efficiency heat pump you can even replace an old boiler and still heat your radiant floors or even radiator heating system.
- No change in building aesthetics: There is no change to the interior or exterior, despite perhaps the addition of an exterior compressor and depending on the system you choose, perhaps some interior ductless heads, which are about 1 foot by 1 foot by about 3 feet long.
- Easier math: you know your current bills, and traditionally a heat pump will cut bills by about a third, give or take depending on the model chosen and climate where you live. No math degree needed for that one. And a contractor coming to give you a quote should be able to help you get a better idea of what you’d save, so you have a much more accurate idea of the payback period for your investment.

I get that it may seem counter-intuitive at first that you landed here on a website about green home-building and the first thing we tell you is ‘don’t bother insulating’, but stone houses really are a special case. They are a part of our heritage and a house is a house, so tearing them down is best avoided if possible. But the reality is that insulation retrofit jobs on them can be a nightmare.
That only leaves choosing between an air source heat pump and a geothermal system. So, we would suggest you get a quote for each and see which suits you better. Geothermal has a much higher upfront cost but offers bigger savings in return, so again you’ll be doing some math to see which is best but at least you know the variables.
What do geothermal systems and heat pumps cost?
As much as we would like to help readers price this out, there is no accurate way for us to do that for you. House sizes vary, climates vary and currencies vary, and each home owner may go to greater lengths of efficiency. So the only way to get an accurate price is a quote from a contractor. You can find local HVAC installers here in the Ecohome Building Professionals Directory
A single-head heat pump in a small and fairly open concept home may create much more efficient living spaces and perhaps you could leave bedrooms cooler, so you may pull that off for about 10K USD. That’s the bottom end and it only goes up from there. As a very general rule, you can probably count on geothermal costing twice as much as an air source heat pump, but it will provide twice as much value.

Now you know about how to restore an old farm house for energy efficiency, how to insulate stone walls, and the best heating systems for old stone houses. Find more pages about geothermal, air source heat pumps and exterior wall insulation in the Ecohome Green Building Guide pages and these pages below:
Find more about green home construction and discover the benefits of a free Ecohome Network Membership here. |
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