Designing Tiny Homes For Cold Climates
Many tiny home builders will claim that their homes are designed for the cold weather but what that typically means is that they have been designed for how cold their local area gets and their knowledge base is usually limited to their local climate as well. A builder in Vancouver, British Columbia needs to account for some cool, wet weather so proper insulation and a small heat source is necessary for the home to be comfortable through the winter. Take that same home east of the mountains and you might have a hard time keeping it comfortable even before winter starts.
The largest factor that is going to affect your homes performance in cold weather is the building envelope. A building envelope is the structural barrier between the interior and exterior of a building. It is responsible for maintaining climate control within the interior of a building. The building envelope includes the roof, walls, subfloor, doors, and windows.
Let's have a look at the specific features in the building envelope that have an impact on your homes performance in cold weather;
This may be the most obvious component people would think of when designing for the cold and for good reason. The type and thickness of the insulation have a large impact on how comfortable the home will feel and how much energy it will require to heat the space. There are 3 main types of insulation being used in the industry currently; fiberglass, rockwool, and spray foam with numerous variations within each type. Their insulating capabilities are rated by what is known as an R-value. The R-value is a measure of how well a barrier such as insulation or a window resists the conductive flow of heat. The higher the number, the better it will insulate.
R-values are calculated per inch so for this comparison we will assume a wall thickness of 3.5" as that is the most common in tiny home construction.
Fiberglass Insulation (R-12) - Fiberglass insulation is one of the more popular options as it is easy to install and relatively inexpensive. As with most insulations it also requires an air and vapour barrier which is crucial to the performance. If the air and vapour barrier is poorly installed it quickly diminishes the insulation capabilities and the home may feel drafty and be difficult to heat.
Rockwool Insulation (R-15) - This would be considered one step above fiberglass in both cost and performance. It offers a slightly better R-value per inch as well as a few additional benefits such as improved soundproofing and fire resistance. Rockwool insulation also requires an air and vapour barrier.
Spray Foam Insulation (R-21 - R-24.5) - There are 2 main types of spray foam insulation; open cell and closed cell. Open cell spray foam has a lower R-value and still requires an air and vapour barrier while closed cell spray foam becomes the air and vapour barrier so for this comparison we will only discuss closed cell as it is a far superior product. While the increased R-value is significant, it is it's ability to perform extremely well as an air and vapour barrier that makes it the best choice for cold climates.
House Wrap / Building Paper
There are many different products available to use as a house wrap such as traditional tar paper or many of the new synthetic wraps. While their performance may vary as far as permeability, the type of product will have little affect on how comfortable the home will be in the cold. The most significant factor with house wrap is ensuring that it is installed properly. A poorly installed house wrap will lead to water getting behind it and into the walls and wet equals cold! When building materials such as wood, fiberglass or rockwool insulation get wet their R-value is reduced to almost zero, even closed cell spray foam is not immune to water saturation. Water infiltration can also compromise the structure over time resulting in major structural damage that can be difficult to detect and repair.
Doors And Windows
Big windows can make small spaces feel much larger and bring in the much needed sunshine we need on a cold winter day but they are also the weakest link in the envelope when it comes to warmth. Glass is a very poor insulator in general however using quality windows is a key component to a home built for cold climates. There are countless different options and combinations of glass and coatings so I will just review a few of the more common ones here to show how it can affect performance. Single pane windows are not suitable for cold climates so they will not be included.
Dual Pane, No Coatings - R-2
Triple Pane, No Coatings - R-3.25
Dual Pane, Low E Coating - R-3.75
Triple Pane, Low E Coating - R-5.5
Dual Pane, Low E Coating, Suspended Film - R-4
Triple Pane, Low E Coating, Suspended Film - R-5.25
These values will vary between manufacturers, and the type and quantity of the films and coatings can be used in various combinations to achieve different results. The other thing you need to consider with tiny homes and windows is the weight. Glass is heavy and although a triple pane window may perform well it may not be worth the additional cost and weight.
Well insulated tiny homes do not require a large heater to keep them comfortable in the winter but it is important to get something that is reliable and properly sized for your home. This is maybe the most common feature tiny home builders are missing the mark on for cold climates. Here are a few of the most common options.
Wood Stove - Wood is a cheap and effective source of heat. Sizing is important here as a unit that is too large will quickly overheat a small space and an undersized stove will require constant feeding to keep the space comfortable. Wood stoves are also not recommended as the only source of heat if you have water in the home as water lines would be susceptible to freezing when left unattended.
Mini Split - These are probably the most common heaters being used in tiny homes as they offer both heating and cooling, they are relatively inexpensive, and easy to install. The one thing that tends to get overlooked with these units is that they are not rated for extremely cold temperatures! Even the highest quality units that are designed for cold weather start losing performance in the -20 to -25 celsius range and most don't perform well even in the -10 to -15 range. The other thing to consider with them is circulation. Most are only designed for one zone meaning the unit has one air handler that is mounted in a central location. This may be fine in a smaller tiny home but as you increase the size of the home it is more likely that you will have a bathroom or loft that is away from the air handler and it will be cooler as a result. You can buy multi zone kits but even with 2 zones you may experience cold spots with multiple lofts and an isolated bathroom.
Electric Heaters - Electric heaters are relatively cheap to purchase, they offer lots of flexibility as they can be placed in multiple locations (as long as there is a power), and they are relatively quiet even with a fan. The downside with electric is that they can consume a ton of power and depending on where you live and your power costs can be very expensive to operate.
Propane Heaters - Again you will find lots of different options and variations with heaters. The 2 main types can be separated by the fact that they either vent to the exterior or vent to the interior. Combustion heaters that vent to the interior are not permitted for use in Canada even though you will find them online and available for purchase in stores so we will only be discussing vented options. Vented heaters exhaust carbon monoxide to the exterior (which also contains moisture) and in most cases draw fresh air for combustion from outside making them much safer for use indoors. Some propane heaters can also be ducted meaning they have the ability to provide heat to various locations in the home for better heat distribution, this can make a huge difference in a larger space.
Although this covers many of the standards you will commonly see in tiny homes being built today it is in no way a complete list of the available options. These are a good representation of cost effective, cold weather performance options that can perform well in any Canadian climate. If you decide that cold weather performance is your highest priority you may want to look at options such as exterior insulation, increasing the wall, floor, and/or ceiling thickness, heated floors etc. There is no doubt that you can get even better performance but in my opinion it is unnecessary and is not worth the additional cost or sacrifice of space.