Insulation--Warm Inside and Out

With colder weather approaching we are giving more consideration to heating our homes now, and to keeping ourselves warm. This week we are going to look at insulation, to see what the numbers mean and understand how it works.

Let’s look at heat, and see how it works. Heat moves via three modes: conduction, convection and radiation. Conduction is you touching something hot directly. Convection involves a medium such as air or water, and heat is carried from one place to another by that medium, such as the warm air coming out of your register. Radiation is how the earth is warmed by the heat of the sun even though there is no air or other medium to carry the heat directly to us through space. The inside of your furnace employs all three of these methods to get the heat to where you want it.

Under the laws of thermodynamics, heat flows “downhill”, or it goes from a hot area to a cooler area. In winter, the outside of your home is cold, and you want the inside to stay warm, so you need a furnace or heater to generate heat inside your home. This heat tries to escape through all the exterior walls and surfaces of your home. Insulation slows this process down and allows your home to stay comfortable. What kind and how much insulation you have will dictate how fast this process is, and how much your furnace has to work to keep your home comfortable. As well, heat rises, so to retain that heat within your home you need more insulation in the ceiling than in the walls.

Most of us are familiar with home insulation, in the form of the pink batts (the 15 X48 in. panels) and the Styrofoam panels, and we have a vague idea about the R number, in which more is better. What does this number mean? It refers to the rate at which heat flows through a certain thickness of material; because it is a reciprocal, a higher number is better than a lower number. It originated before metric units existed so it is based on BTUs (British Thermal Units, a way of measuring the quantity of heat) per inch per time unit. Europe uses a U value, in which lower is better.

Insulation works by trapping many tiny pockets of air within a structure of some kind. These pockets are separated from each other and each acts as barrier to the transmission of heat. Fibreglass, Styrofoam and blown cellulose all share this property. The foamed urethane that you can spray into the cracks around windows starts as a liquid but as the polymer forms and hardens it gives off carbon dioxide gas which becomes trapped in tiny cells, giving the insulation value. Another key property of insulation is its non-flammability. Fibreglass is non-flammable, and blue and pink Styrofoam is treated to be non-flammable. White Styrofoam, also called beadboard, has to be covered with a non-flammable layer, often plasterboard, to meet building codes. Blown cellulose is made from waste newsprint and is treated with chemicals called borates to resist mould, rodent damage and to reduce its flammability.

Fibreglass insulation is made from glass in the same way as cotton candy. It is heated to melting and spun through fine holes to make fibres. These fibres are collected and formed into batts and treated with a non-flammable resin to holds them together. Interestingly, FG insulation can use recycled glass, including coloured glass, which is often difficult to recycle. Some brands contain up to 90% recycled glass.

In the post-war building boom of the 50s and 60s, energy costs were not a consideration and thousands of homes were built with 4” cavity walls with minimal thought given to insulation. As energy costs rose in the 70s we began to see more attention paid to this area, and better methods of insulation and stricter codes came into effect. Today most new homes have 6” walls with a minimum R12 and often R20, and higher in the ceilings. Many of those older homes have been successfully retro-fitted with improved insulation to lower the heating costs.

Choosing the right insulation can be a bit daunting. As far as strict efficiency goes, pink or blue Styrofoam boards have the highest R-value per inch, about 5, with fibreglass and cellulose about R3.5 per inch. This however does not factor in cost and ease of use, which are major considerations, especially in retro-fitting an existing building.

An effective method of insulating windows is to use transparent shrink film, held in place by double-sided tape and tightened with a hair dryer. This traps a layer of still air in front of the window and lessens dramatically the amount of heat that escapes through the window, as well as blocking drafts around the window. Your home fix-it store has economical kits to do this.

With warmer summers now common, many of our homes are air-conditioned. The same principles apply as in winter, except the heat is trying to go the other way. Your air conditioner is removing heat that makes its way into the building, or is generated inside. That is why you turn off unnecessary lights and use the microwave instead of the stove when you are running the AC, and a well-insulated home is easier to air-condition as well as heat.

Canadians have an intuitive feel for insulation, and we must do a better job of minimising our consumption of energy. If we apply insulation carefully, to make best use of its properties, we can make significant progress towards energy conservation and save money as well.