They really didn't have a choice, and they insulated their bodies, not their houses.
A tweet was forwarded to me from a discussion about house design in cold climates:
Was insulation extremely expensive and or heating gas super cheap back in the day? I don’t understand how people built houses in Canada that just leak heat out— ________________ (@phillmv) August 25, 2019
The answer is, as always, complicated.
First of all, the houses didn't "just leak heat out." Wood is not a terrible insulation. People who lived in log cabins basically had walls of about R-10. You spend your winter chinking the logs so that you don't have drafts, and it gets quite cozy, especially when the room is relatively small and the entire family and maybe their animals pack inside. Dried manure had a pretty good R-value too, if you really want to go back a few years.
Houses built a hundred and fifty years ago were built out of brick or stone, then had an air space, lath and plaster, often made with horse hair. It had a lousy U-value, or thermal transmittance, the amount of heat that goes through the wall. Its reciprocal R-value, the resistance to heat transfer, is the way we measure heat loss today, but that's not the only thing that matters in a wall. A UK study of historic buildings with brick walls (PDF here) found that they performed much better than expected:
Thermal performance for traditional walls is underestimated- The average U-value of walls measured in situ at the eighteen properties was 1.4 W/m2K. This indicates that the industry-standard default U-value of 2.1 W/m2K for a solid (9-inch) brick wall, used in energy-performance assessments, underestimates the thermal performance of the wall by approximately one third.
The walls also have a lot of thermal mass, so when they get warm, they stay warm longer. So if a stove is going in the middle of the room and warming the wall, the wall will act as a thermal flywheel, keeping the heat even day and night. The heat would move through the wall, pushing out moisture and keeping the brick or stone from freezing and cracking.
Another important factor for comfort historically was controlling drafts, so people had thick velvet curtains and draft stoppers at doors; they stayed warmer with interior design. They did their best to keep the heat from leaking out, but they couldn't stop all the leakage; all of these fuel-burning systems from fireplaces to stoves to furnaces needed a supply of fresh air for combustion, so it actually was important that the house leak a bit of air. The rooms were never going to be a comfy temperature, and the people in them were warmed by direct radiation from the heat source, sitting by the fire or the stove.
Houses were designed differently too; even in the middle of a farm they would be two storeys tall so that heat would rise into the bedrooms above. They would be smaller and squarer because not only was fuel expensive, schlepping wood or coal was hard work. You can see in this photo of William Lyon Mackenzie's urban townhouse in Toronto, built 1858, that they filled in the inefficient fireplace and stuck an enclosed wood stove in front to save fuel and get more radiant heat. But in fact, they only lit that when guests were visiting; For most of the winter, the Mackenzie family huddled in the basement where the kitchen was.
Clothing was the predominant insulation.
But most importantly, people had their own furnaces, their bodies, and their own insulation: clothing. As Kris de Decker notes in Low Tech Magazine, clothing reduces heat loss for humans in the way fur does for animals.
Insulation of the body is much more energy efficient than insulation of the space in which this body finds itself. Insulating the body only requires a small layer of air to be heated, while a heating system has to warm all the air in a room to achieve the same result.
So you dressed warmly and sat by the fire or the stove in your big overstuffed chair. This is what has changed, more than anything: our expectations. As John Straube notes in a wonderful podcast on Green Building Advisor,
People used to put up with cold places in the winter and hot places in the summer. And we’ve gotten spoiled into saying, “No, I want a more comfortable environment.” So, the temperature ranges that are tolerable have narrowed quite considerably.
So how did people stay warm?
So this is the real answer to the original tweet's question: Heating fuel was expensive, so you used it sparingly and locally, in the room where you needed it. Insulation barely existed, but those old walls were better than people give them credit for. Interior design kept you warm, with wing chairs and heavy drapes. But most importantly, people dressed for the season and insulated themselves.
Central heating slowly changes the picture.
When central heating became common in houses, their designs stayed vertical, since before electric pumps or fans were common the water in radiators and the air in ducts circulated by convection, with hot air or water rising. As it became more common, and people started expecting the room to actually be warm all the time, separate insulation became a necessity, especially in wood frame houses. Sawdust was common; so was vermiculite, a rock that expands when heated. Cork was expensive but was used in iceboxes and famously, in Nansen's Fram.
But these materials, unlike a solid stone or brick or adobe wall, were not homogenous; people quickly ran into problems with moisture. People are still running into problems with moisture from not understanding how it travels through walls.
Rock wool was developed in 1897; Weyerhauser invented cellulose insulation batts in the 1920s, marketed as balsam wool; and Owens-Corning introduced fiberglass insulation in 1938. Post-Second World War, we got plastic foams.
Today, of course, we are are again living in a time where we want to use less fuel, not because it is expensive but because of carbon emissions. Those of us who still live in these leaky old houses could learn from our Victorian forebears and do what Kris De Decker suggests, which is put on a sweater:
The energy savings potential of clothing is so large that it cannot be ignored - though in fact this is exactly what is happening now. This does not mean that home insulation and efficient heating systems should not be encouraged. All three paths should be pursued, but improving clothing insulation is obviously the cheapest, easiest and fastest way.
In my own 100-year-old house, I went for interior window inserts and a more efficient heating system. Come this winter, instead of cursing my dumb thermostat and undersized furnace, I will remember Kris's advice and put on a really warm sweater.