The Myths About Vapour Barriers

A vapour barrier (VB) is a material that offers a high resistance to the diffusion of water vapour. It is used to separate an environment which is at a high vapour pressure from an adjacent one at a lower vapour pressure.

For best results, it is important that the vapour barrier be continuous, but it

How do we prevent water vapour from migrating outside?

The main way is through vapour barriers. For many years, designers were taught that the VB was a major requirement for insulated walls in order to control the diffusion of water vapour into the colder reaches of these walls, where it could condense and stain the finished surfaces or, worse, initiate the deterioration of the affected materials. Eventually, the designers would use that in a continuous and airtight manner. It was always possible to achieve that. Current practices still use this.

When it became obvious to researchers in the 1960s that air leakage into the walls and roofs was a more important source of water migration, authorities began calling for a "continuous vapour barrier."

It was found to be close to impossible, considering the materials that were being used mostly polyethylene and other not-so-durable products. Still, vapour barriers need to be sealed so that there is no accumulation of water vapour near the walls.

What is the definition of a vapour barrier? Does not have to be perfectly continuous. The key factor is that it must be located on the warm side.

Unsealed laps or minor cuts do not affect the overall resistance to diffusion significantly. The vapour barrier must also be located on the warm side of the insulation or at least in a location in the wall near enough to the warm side to remain above the dew point temperature of the indoor air during cold weather.

The building code defines it as:

A material that has a water vapour permeance less than 60 ng/ (Pa/s/m2) when measured in accordance with ASTM E96, "Water Vapour Transmission of Materials", using the desiccant method (dry cup).

That plays an important role when selecting materials in the design of a wall assembly.

In a typical wall assembly the VB must be located on the warm side of the insulation. It can be located somewhere else depending on where you are in the country and what are your degree days. There are figures that you can look up for different cities and what building code is applicable. When you study these numbers they will be expressed in a ratio (0.3, 0.35, 0.4 etc) A ratio of say.3 means that the ratio of the outboard to the inboard of insulation of the vapour barrier can't exceed that. This means that you can't have more than 30% in the inboard side. This is usually not a problem as people usually just keep it on the inside. However there are several other materials that can act as vapour barriers.

For example, plywood is water permeance less than 60 ng/ (Pa/s/m2) and technically it acts as a VB. As such when introduced on the exterior of the building it will act as a vapour barrier a will trap moisture within the wall assembly which in turn will cause moisture problems. Because of this most building codes now require that plywood and OSD be installed with gaps at their joints to allow the moisture to escape to the exterior.

Continuity and durability is not as important with vapour barriers as it is with air barriers. Partly because a VB is usually is on the inside and protected from the elements and covered by another material such as gypsum board.

Now if you're wondering why most builders, designers and building departments require that vapour barriers be continuous and be properly sealed and caulked at all joints is because in most cases the vapour barrier is also acting as an air barrier. Because it is located on the warm side of the insulation it does have to be air permeable and as such can act as both an air barrier and a vapour barrier. This does not elevate the fact that another air barrier would be required on the outside of the building to prevent air and water from penetrating the wall assembly.

As you can see selecting proper materials to install on your home is not as simple as looking at the R-value per inch or the price of the product, but also how it will perform within the assembly. Make sure you perform the proper research or speak to an experienced building and design professional.

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Facts About Modular Homes

What is a modular home?

Modular homes are homes that are built in sections in a factory where they are protected from weather elements and delays. They are built using efficient construction technology with minimal material waste. The house is built to the same local building codes that site built houses are and follow strict quality control standards. Because modular homes must be transported to the build site, they are constructed in a way that makes them much stronger than site built options.

Are modular homes are cost effective?

Modular homes are very cost effective. They are built in an efficient manner with little time loss as well as little materials waste. Materials can also be purchased by the manufacturer in bulk. These costs are usually passed on to the consumer. Depending where the build is, the construction costs of a modular house average 10-35% less than a similar site build one. These houses also appreciate in value in the same way other homes do.

How long does it take to build a modular home?

The length of time it takes to build a modular dwelling will vary based on the design, the manufacturer, and the on-site contractor. Most modular houses can be built in the factory within 1-2 weeks. The process is much faster than site built because weather delays are avoided due to the factory setting. Once the home has been completed in the factory it will be transported to the building site and then it usually takes another 2-4 weeks to complete the construction.

How do modular homes impact the environment?

Being environmentally friendly is becoming more important to many consumers and home builders. Modular constructed homes are very energy efficient. They have well-insulated walls, as well as sustainable construction materials.

Are modular homes well constructed?

Many homeowners mistakenly believe that modular houses are not as well constructed as site built homes. This is not true. Because factory homes must be transported they are especially strong and have to withstand conditions that site built homes do not. These homes also go through number of inspections, more than a traditional home, to insure quality. Every step of the construction process is controlled and professionally supervised. These homes have greatly improved over recent years and it is now becoming difficult to distinguish one from a site built home.

Is there any variety?

There are a wide variety of floor plan options for modular homes. Vaulted ceilings, fully equipped full size kitchens, walk in closets, wrap around porches and many other features are available on these factory constructed homes. They can even be customized to fit the needs of the family. Upgrades are also available as well as different exterior finishes. Factory built homes of today are constructed of the same materials that traditional homes are.

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