Solariums have been gaining in popularity over the last 20 years, as many homeowners have found them to be a very enticing solution to brightening up a long winter. They are made even more appealing by the many manufacturers who offer solariums at very attractive prices - especially when compared to adding a home extension of comparable size, the cost per sqft is much lower with special offers on Solariums.

Just think about it - who doesn’t dream of living in a bright house that invites in the warm rays of the sun on a cold winter's day? A solarium seems to be the perfect solution - they are brightly lit and heated by the sun and, in addition to increasing your indoor living space, they allow you to feel like you are connected with nature no matter the season.

But when you look past the initial attraction and instead evaluate them based on their energy footprint, durability and comfort, they are unfortunately not well-suited to cold climates such as we have across most of Canada.

Prefab kit solariums:

Some solariums are bought as kits and used exclusively as living space, others are used for growing vegetables and even fruit. Strictly speaking, a solarium is not a greenhouse, but can be used as such.

The typical solarium is usually a glazed space adjacent to a dwelling, separated by an exterior wall and accessed through a door. Roofs are sometimes glazed, but not necessarily. Other solariums are permanently integrated into the living space and cannot be closed off from the rest of the home.

Most commercially available solarium kits are constructed with wood or aluminum frames. It goes without saying that the choice of materials and the surface area greatly affect their price, but that also applies to their durability and energy performance.

solarium sunroom
Solarium/Sunroom kit addition for extra space, but are they the bargain they may seem? © Lindal Additions via Flickr


Passive heating in solariums - expectations vs reality:

The concept and common sales pitch for solariums are just great; capture the sun's rays to reduce your overall winter heating costs. Their effectiveness in this capacity has been well-documented in moderate climates such as in Europe or even in the milder regions of the United States. However, it's a very different story in Canada or cold climates! Here is what you can realistically expect from a solarium during each season in a cold northern or central mainland USA climate:

Winter days: even in the dead of winter, a solarium will heat up significantly, so much so that it may probably even overheat.

Due to the lower orientation of the winter sun and the absence of leaves on most trees, the sun's rays will easily reach far into a solarium, even those that don’t include a glazed roof. This can be a good thing, if the solarium is carefully designed - but most aren't.

However, on cloudy days, the interior temperature will not likely warm to a comfortable temperature. And depending on the configuration of a specific solarium, it may often be difficult to maintain a comfortable living temperature without a supplementary heat source and a well insulated slab on grade foundation.

Winter nights: depending on the amount of thermal mass in the room (stone, masonry, brick, etc.) to act as a thermal battery for storing solar heat, varying amounts of heat will be absorbed and stored when the sun is up, and released later when the sun goes down and the room begins to cool. But once that supply of heat is depleted, and in the absence of a supplementary heat source, the room will rapidly lose energy to the outside through the large glazing area.

As the structure and frame have virtually no insulation value, they will act as a thermal bridge, and quickly draw the heat out of the solarium. In short, heat accumulated during the day will be lost at night, and the overall energy balance will often amount to a net heat loss rather than the commonly advertised net heat gain.

Durability is also a serious concern, as warm, humid air condenses on the cold interior surfaces and leaves behind moisture that can run down the frame and glazing and damage parts of the structure or furnishings.

Solariums; The experience of an expert:

Ecohome’s engineer Denis Boyer is an expert in thermodynamics and energy efficiency and, conveniently for us, used to live in a house in a cold climate with a solarium. This makes him uniquely positioned to report on their performance.  

Living in an open concept home with a four-season solarium overlooking the living room and the kitchen, his solarium consisted of an aluminum structure with a double-glazed roof and walls. His experience was such that in winter, the aluminum structure would become very cold to the touch, and frost would often appear on the windows. "We had a sofa leaning against the glass wall in the middle of the solarium, and when sitting there in winter it often felt like there was a window open.” Denis attributes this sensation to the natural convection of warm air rising and cool air dropping.

“The warm air in the center of the room would rise to the ceiling, and as it touched the cold surfaces of the roof and walls, it would cool and drop down along the vertical glazing surface, creating the sensation of a rather annoying cold breeze.” (read about designing for thermal comfort)

In addition, he mentioned the cold windows would draw all the heat radiating from the room (and its occupants) and often make the room quite uncomfortable, not to mention that the solarium contributed to much higher heating bills.

Spring and fall:

If a solarium is facing south and there are no leaves on trees or anything else to block the sun, you can expect them to constantly overheat during the spring and fall months.


They will for the most part, be hot by day as well as night. This limits the use of a solarium as a living area in the summer unless they are air-conditioned, which would be another nail in the coffin of the ‘energy efficiency’ argument.

Overall performance of Solariums:

The idea that a solarium will heat the interior of the building in winter and reduce its energy consumption unfortunately does not seem to materialize in all but the warmest regions of Canada, like Southern Ontario and perhaps the sunnier regions of coastal or central British Columbia. Generally speaking, the further north they are built, the greater the net heat loss will be.

Shading from nearby deciduous trees may extend the annual amount of usable time a solarium will offer, by reducing the input of unwanted heat in the summer, yet also allowing the winter sun to enter.

On the other hand, Denis Boyer's experience in terms of what benefits tree coverage offers is mixed;

“Leaves offered some shading and respite from the sun’s rays, but they would often fall and stay on the glass roof. Thus, in addition to blocking the light, they ended up rotting, so it was therefore necessary to climb on the roof from time to time to clean it, a rather risky endeavour. It was also essential that we kept nearby trees well-pruned, or risk damage from branches that could break and fall under the weight of snow or ice. We often forget that a solarium has a more fragile roof and is in constant need of maintenance."

Our recommendations for the passive heating and sunlit living space in Solariums:

Comfort, durability and energy efficiency are best achieved if passive heating strategies are designed as an integrated part of the building envelope. This is best served by choosing high-performance windows that would ideally be triple-paned.

Additionally, including darker colored materials with significant thermal mass in the direct path of the sun can help optimize heat gain and keep interior temperatures balanced. The ideal design would absorb as much solar radiation as possible in the day, lose as little as possible at night, and include materials with high thermal mass and dark color in the direct path of the sun to absorb heat and balance temperatures.

"The extreme variation of temperatures between summer and winter in our Solarium took a significant toll on the junction between the aluminum structure and the glazing. Leaks in the frames would regularly develop and require swift repair to avoid damage to surrounding materials” says Denis, though he goes on to add - 

“Despite all the disadvantages, including frequent discomfort, high heating bills, water infiltration and regular required maintenance, there was no denying the attractive atmosphere of our solarium with such an input of natural light into our home.”

For those who still want a solarium…

If you are still tempted to install a solarium after considering the downsides listed above, here are the recommendations of Denis Boyer - opt for triple glazing to minimize convection, increase comfort and improve efficiency but consider selecting a low-e glazing that will prevent overheating most of the time, unless shading is readily available; be diligent with maintenance of the junctions between the frame and glazing; install a heat pump to reduce heating and cooling costs in winter while ensuring comfort in summer; avoid a glazed roof, and opt for a light-coloured exterior structure that will reflect light with a dark colored interior area exposed to the sun for maximum winter heat gain.

Solariums conclusion:

It simply cannot be denied that on its own with no climate control, a solarium will for the most part, be either too hot or too cold. It will not bring with it energy savings, it will not be useable much of the time, and it will likely require more maintenance than the rest of your house. We would instead float the idea of a conventionally built addition, with an energy-efficient wall assembly that includes large, high-quality windows.

 If your desire is to use a solarium as a makeshift greenhouse for growing ornamental plants or perhaps food, that presents even greater concerns. A greenhouse full of plants will have high levels of relative humidity, and to allow that environment to mix with that of the rest of your conditioned space will increase the overall humidity levels in your home, for an idea of the principles involved, see why earthships don't work in cold climates here.

All that said, the appeal of solariums or a greenhouse in winter is pretty strong, so for those determined to bask in a warm sunny enviroment, here is a guide detaling the best practices for greenhouse construction in a cold climate.

Now you've learned all about Solariums in cold climates, to better understand the principles of Passive Solar home design, and how to heat homes with the heat of sun, see here, for a finely engineered solution to high performance homes check out all you need to know about Passive House certification here from North America's favorite no-nonsense Green Building Website, EcoHome