Peace and Environment News* February 1995
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Peace and Environment News * February 1995 |
by Vince Catalli
 CANMET—Advanced Houses Program |
Most homes built prior to 1975 have little to no insulation. Homes which were built between 1975 and 1985 have approximately half the amount of insulation required to meet today's standards. Therefore most homes lose considerable amounts of heat over the winter months. The end result is energy overconsumption, drafty interior spaces and high operating costs.
Of the energy used in a typical home, 70 percent is related to space heating. This amount can easily be cut in half through retrofitting your home with insulation and better windows. This article will discuss some issues that you should consider if you are thinking of making your home more energy efficient.
Control of heat flow
Heat loss in homes is directly linked to the levels of insulation in the ceilings, walls, windows, doors, floors and basement walls, and the rate at which warm air leaks through the home. The key to having a house that is energy efficient is a well insulated and airtight house envelope.
Insulation is a very important component of all exterior walls. It acts as a layer which slows the rate at which heat is lost to the outdoors. Heat loss is a natural result of the fact that heat always flows from warm to cold.
Insulation is manufactured and sold by its thermal resistance value (called the RSI value), which is a precise measurement of the resistance of the insulation to heat flow. The higher the resistance value, the slower the rate of heat transfer through the insulating material.
One brand of insulation may be thicker or thinner than another, but if they both have the same RSI value, they will control heat flow equally well.
Some insulation materials are marked with both RSI and R values. RSI values indicate thermal resistance in metric terms, while the R value represents Imperial measurements. Be careful not to confuse the two.
For insulation to work effectively, it must be installed properly. I recommend that you contact Canada Mortgage and Housing Corporation for more detailed information by calling the Canadian Housing Information Centre at 748-2241. Keep in mind the following guidelines that apply wherever insulation is installed:
How much insulation?
Your choice of how much insulation to add will depend on many factors.
To help you make your decision, you may wish to compare your plans with the National Building Code recommendations (listed below) for new housing. These insulation levels are highly recommended as a minimum level for the retrofit of existing housing.
| Zone | RSI value | R value |
|---|---|---|
| Walls | 3.6 | 20 |
| Basement walls | 2.2 | 13 |
| Roof or ceiling | 5.6 | 32 |
| Floor (over unheated spaces) | 4.7 | 27 |
Controlling air leakage
To be effective, insulation must trap still air. It must be protected from wind blowing through from the outside and from air escaping from the inside of the home.
The wind barrier is located on the outside of the envelope to protect the insulation from the circulation of outside air. Standard building materials such as exterior sheathing and building paper or new sheet materials such as spun-bonded olefin act as the exterior wind barrier.
The air barrier blocks air flow from the inside to the outside. By doing this it serves two important functions.
The air barrier is usually installed on the inside of the envelope, where it is kept warm. This protects the material from temperature extremes, which can affect its durability. When installed on the warm side, the air barrier is often combined with the vapour barrier. If located on the inside, the air barrier will also prevent heat loss when air circulates from the house into the wall space.
To be effective, the air barrier must be:
Selecting Windows
When choosing windows for your home, the main environmental concern is energy efficiency. Windows make up on average 15 to 40 percent of the wall area in a house, and have the potential to allow large heat losses. In the average house, heat losses through windows can represent 22 to 37 percent of the total heat lost. Careful window selection when building a new house or renovating an old one can make a significant difference by helping to reduce heat loss.
Windows come in a variety of shapes, sizes, and material combinations. Each type of window design has different attributes that affect the overall performance. Knowing what to look for in a window is not an easy task, given that window technology has undergone rapid developments in the past few years.
The standard double-glazed sealed unit is quickly being replaced by windows with improved thermal performance, which are known as high-performance windows. There are several features to consider when selecting high-performance windows. The main characteristics which should inform your decision include: special coatings, multiple glazing, framing materials, gas fills and low-conductivity spacers.
Keep in mind that your window should comply to CAN/CSA-A440-M90 standards. This ensures the highest quality presently possible. Be sure to look for this label on any window you are considering using.
Coatings
Thin metal coatings (low-emissivity or low-E) applied to the glazing will reduce the amount of heat which will radiate from the warm inside of the house to the cold outside. Window coatings are either soft or hard.
A soft coating is a thin metal layer sandwiched between two protective oxide layers, applied to the inner glass surfaces in sealed units. Soft coatings are easily damaged, but have higher insulation values and will allow for some solar heat gain.
A hard coating is a tin-oxide coating fused to the glass surface. Hard coatings tend to be more durable than soft coatings. They do, however, have lower insulation values and tend to allow full solar heat gain.
Coatings can also be applied to polyester films that can be installed between two glazings and thus provide a lightweight third glazing.
Gas fills
Sealed window units have air spaces between the glass layers. This air space can be replaced with inert gas such as argon or krypton, which improves the thermal performance of the unit. Research indicates that the careful sealing limits gas loss to less than 2 percent annually. A gas fill could therefore remain effective over the expected twenty-year life of the window.
Spacers
Spacers are used to separate the glass layers within the sealed unit. Metal spacers that readily conduct heat are increasingly being replaced with low conductivity spacers. In fact, heat loss can be reduced by 20 percent using energy-efficient spacers such as rigid foam, butyl tape with an aluminum strip, fibreglass extrusions and wood.
Frames
The frame in a conventional window is typically 25 to 30 percent of the total window area. Window framing materials include wood, polyvinyl chloride (PVC), aluminum, fibreglass and composite frames. Each varies in strength, longevity, air leakage, and insulation value.
The insulation value of a solid wood frame or good quality vinyl frame is about the same as the glazing of a conventional double-glazed window. Aluminum frames, even those with thermal breaks, are often less efficient.
Well-designed PVC or fibreglass frames have slightly greater insulation value than wood, particularly if hollows in the frame are filled with insulation. However, a poorly designed metal-reinforced PVC frame may not perform as well as wood owing to thermal bridges and greater air leakage at low temperatures.
Reducing the area of the window frame and choosing narrower frames with higher insulation values is therefore desirable. Fibreglass frames offer insulation and strength in a low profile frame contributing to some of the highest energy ratings.
Glazing
The goal of any high performance window is to admit maximum light and solar heat gain in winter months with minimum loss of heat. Standard double glazing loses about ten times as much heat as the same area of wall with six inches of insulation. High-performance windows (double and triple glazing) not only reduce heat loss but, through solar gains, can be net contributors to home heating. They also make houses feel more comfortable by reducing drafts and by permitting higher interior humidity levels without condensation forming on the windows.
The bottom line
For renovation or replacement, the key to good window selection is to obtain maximum energy efficiency at reasonable cost and to meet specific needs. You should select windows that incorporate two or more glazings, low-E coating, inert gas fill and insulated frame and spacer materials.
Many quality high-performance windows are being marketed for little more than traditional windows. Studies show that their modest premium will pay back many times over the life of the windows. In addition, high-performance windows add comfort, require less maintenance, provide immediate reduction of energy costs and add to the desirability and value of any home. It is clear that by investing in high-performance windows, home owners reap a number of benefits. Next time you are in the market for windows, keep these ideas in mind.
Renovations, additions and new construction for homeowners can be very confusing. Many choices and difficult decisions will be made along the way, and you as the homeowner should be in control of those decisions. Left to themselves, contractors more often than not will base decisions on lowering costs rather than on long term energy conservation and environmental criteria. It pays to do research or get professional advice to determine your priorities before hiring a contractor. Spending some time to consider the design options and the environmental and energy benefits at the initial stages can pay off in the long run.
It is a good idea to have your construction drawings done by an independent consultant with no relation to your contractor. It is through developing these design and construction drawings that you will be able to determine what it is you want. These drawings will guide your contractor in the right direction by prescribing the materials and construction techniques that are environmentally and energy effective. The end result is a design that you will be proud of, and you will know for certain that you have participated in the decision-making process. Remember, don't be shy about asking questions. If they don't know the answer, ask them to find out. After all, you are paying.
If you have a question about a renovation or retrofit you are planning, send a brief description of your problem, along with your name and phone number, to the Peace and Environment News, c/o PERC, Box 4075, Station E, Ottawa, K1S 5B1. Your question will be forwarded to Vince Catalli, and he will reply through the Peace and Environment News or by contacting you directly.
Vince Catalli is an intern Architect with by dEsign consultants in Ottawa. He is also Chair of the Environment Committee with the Ottawa Regional Society of Architects. Readers with specific questions can contact him by calling by dEsign consultants at 230-5776.
Converted June 14, 2000 - Lg
To follow up on this article, contact the author or the organizations/individuals mentioned; do not contact the Peace and Environment Resource Centre - we cannot provide follow up or contact information. This article is an archival copy of the printed one in the Peace and Environment News (PEN). Viewpoints expressed should not be taken to represent the opinions of the Peace and Environment Resource Centre, the PEN, or our supporters.
