Actually, I think our building codes disagree, and it could be because of climate conditions. Year-round temperatures here in southern Ontario (about as far south as you can get in Canada) vary from the high 90s in the summer to probably -30 in the winter, although I haven't seen that latter one for several years. These are Fahrenheit degrees, by the way. The rest of the country uses Celcius (what I always knew as Centigrade, but you know how whacky governments can be.) Summer humidity is often quite high.
The building code here specifies a continuous vapour barrier on the inside face of the framing of exterior walls and ceilings of all heated spaces. This is generally polyfilm plastic sheeting, although a sealed application of extruded styrofoam sheets or sprayed-in-place foam is also acceptable. This includes sealing around all plumbing and electrical fittings which open into the heated space. Most builders use a house-wrap product, such as Tyvek, on the exterior, applied over the rough sheathing, over which is applied the finished siding or brick veneer. Also, there are requirements for venting uninsulated attic spaces, usually a percentage of the attic's square footage. This latter requirement is an important part of the insulation/vapour barrier package.
The separate interior vapour barrier requirements date back to about the mid-'60s, I think. Houses built in the '50s and earlier didn't use one, although in those days, most interior walls were painted with oil-based paints, which were considered adequate for such purposes.
My house is over 20 years old, and built with mostly a poly film interior vapour barrier, although I did use 2" extruded foam on the underside of some rafters which form a ceiling in part of the house. I did most of the construction work myself, so I'm quite familiar with how it was put together. My heating and cooling costs are, I'm told, very reasonable for a house of this size, and there is absolutely no evidence of mould or rot anywhere, including in walls that have been opened to perform "renovations" for the person who runs this circus.
I have worked on renovations in some older houses (pre-1960s), and in some cases found mould damage and/or rot, although most such incidences seemed more related to leaks than mere vapour incursion. I did see one place that had an exterior vapour barrier and none on the interior and it was in rough shape - that particular area appeared to be a fairly-recent addition, probably done by an amateur. The older part of the house was in better shape.
Generally, the building code for your area is a good guide to follow, although not always infallible. Some years back, the provincial government was giving grants to people who upgraded their insulation (usually older houses with no insulation) by having urethane foam sprayed into the wall cavities. Some years later, it was discovered that this material continues to emit dangerous levels of formaldehyde for years after the initial application. Many spent large sums of money to have the material removed, while others opted for whole-house air exchange systems, and to this day, if you sell such a house, you are required to report the presence of such insulation.
Wayne
yougottawanta Wayne, I think you do not understand in part my message and that we agree in whole or part. First let me clear up one item. I do agree that a vapor barrier is important on the exterior wall of the house against the exterior side of the sheathing. A vapor berrier is necassary and code required on insulation on the exterior side of the insulation . However. Plastic should never be used as a vapor barrier on the interior side of the wall or the exterior side. As I stated earlier it will lead to rot and mold.
Wayne, I think you do not understand in part my message and that we agree in whole or part. First let me clear up one item. I do agree that a vapor barrier is important on the exterior wall of the house against the exterior side of the sheathing. A vapor berrier is necassary and code required on insulation on the exterior side of the insulation . However. Plastic should never be used as a vapor barrier on the interior side of the wall or the exterior side. As I stated earlier it will lead to rot and mold.
I have never heard anyone but you claim that a vapor barrier should never be used on the inside of exterior walls. Every person or article I have ever heard or read says that you should ALWAYS use a vapor barrier on the heated side of an insulated exterior wall or ceiling.
If you doubt that advise, find a heated building with single glazed windows in the winter. The INSIDE of the glass will get so wet that you can write your name in the moisture. The cold side will remain bone dry. Find a house with double glazed windows where the seal on the windows has failed. The interior between the pieces of glass fills with moisture.
Warm air holds more moisture than cold air. When the warm air hits the cold glass the moisture is deposited on the glass. When warm air rises into the colder air above and cools, the moisture comes out of the air in the form of clouds.
Unless you live and work in the tropics, where the outside is always the heated side, your advise is in error.
Dave
Lackawanna Route of the Phoebe Snow