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There's nothing new about passive solar

Updated: Apr 9, 2020

The costs of fossil fuels continue to rise, both in dollars and in damage to the planet. As a result energy efficiency has become a top priority for homebuyers. Today's homes meet this demand is several ways. Heating and cooling systems are increasingly efficient so we pay less to heat and cool air. And houses are tight--that is well-sealed and well insulated to keep warm air from escaping in the winter and cool air from escaping in the summer.

Of course nobody was much concerned about saving energy dollars until the last quarter of the 20th century. And certainly nobody was thinking about saving the planet by conserving energy resources. However early houses didn’t have central heat and they didn’t have central air. So builders were simply looking for passive ways to make homes more comfortable. Fortunately for today’s old house dwellers, the strategies used then still enhance the comfort of older homes and reduce reliance on fossil fuels.

The first line of defense was carefully planning how the house was sited in relation to the path of the sun. Today we would call this passive solar. Old house builders didn't just think about the orientation of the roof (as the drawing shows) but also about the layout of the rooms. Cooking on a wood or coal stove kicked off a lot more heat than a modern kitchen. So, the kitchen is usually on the cooler north side. But the parlor, on the other hand, would be on the south side to enjoy the warmth of the sun. See if you notice this the next time you are in a house built before the 20th century. And while modern stoves don’t heat up the kitchen so much these days, we still enjoy a sun-drench parlor.

To this day, builders of custom homes still consider the sun’s path. But developers working with standardized house plans often don’t. Typically they’ll just plop the house on the lot with the front door and the big windows facing the street. Older homes in cold climates like the northeast on the other hand, often have the most windows facing south.

Landscaping has long been used to advantage too. Deciduous trees would be strategically positioned for shade in summer--and lose their leaves to let the winter sunlight through. Builders also use evergreens as windbreaks.

Many old houses have wonderful deep porches—great places to sit in a rocker,

enjoy the shade and chat with passing neighbors. But a well-designed porch does

more than that. Smart builders planned the depth and height of the porch to admit

low winter sunlight and shield out high summer rays.

Removable awnings were another way of adapting to the sun’s path. They were useful on the south side of the house, especially if there were no shade trees. In the photo shown here, awnings add shade to the porch as well as the south-facing windows.They also add quite a bit of charm. You can still order custom awnings today. They’ll lower your summer cooling bills.

Another passive solar trick in the old house builder's bag is thermal mass. We’ve all walked into an un-air-conditioned old house in the summer that’s comfortably cooler than the outdoors. That’s thermal mass at work. While thermal mass and modern insulation both help keep homes warm in winter and cool in summer, they work in very different ways. Essentially, insulation works like a thermos—it blocks heat from flowing in or out. Thermal mass on the other hand acts like a battery. It stores heat. Then, once it’s saturated with heat or the ambient temperature drops, it begins releasing that warmth as quickly as it absorbs it.

Before the advent of insulation, builders relied on thermal mass to help keep homes at a comfortable temperature. They did this by building with solid stone or brick. In the case of timber frames, they often filled the walls with ruble stone. The ruble didn’t have a structural purpose--it didn't hold the house up, it just added thermal mass. Old-timey plaster also has more thermal mass than modern drywall.

Dense materials like masonry slowly absorb lots of the sun’s warmth during the day and release it during the night. As a result the home’s temperature is mediated. It’s cooler on summer days and warmer on winter nights.

Now in our climate, thermal mass alone usually isn’t enough to keep a home at the nice steady temperature modern folks have come to expect. But it’ll still reduce reliance on mechanically heated or cooled air—especially if the house has been retrofitted with insulation.

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