Is Polyethylene Creating Potential for Mold?

Lucas Hamilton

Last week, I was in Calgary, Alberta, Canada for one of CertainTeed’s Be Certain events conducting training sessions on designing for Mold and Moisture control in buildings.  In preparation for the sessions, I ran computer simulations on typical construction models in Calgary.  This gave me a better awareness of how they build as well as scientific understanding of construction practices in the province.

In extremely cold and dry climates like Calgary, which is similar to Colorado, use of exterior insulations is very common.  This practice emphasizes the use of insulation on the outside of the building.  This cuts down the thermal connectivity of the building frame to make the building more energy efficient.

The 2009 International Energy Conservation Code (IECC) mandates the use of exterior insulation in cold climates. However, when you do this with traditional materials such as rigid foam plastics, you may reduce the potential to dry a building to the outside.  If a wall gets wet normally, dry air on the outside can act as a reservoir to dry the building. When insulations like extruded polystyrenes are used on the outside of the building, while being extremely energy efficient, they may reduce this drying potential.

Some new computer modeling tools have the ability to create window leaks and other scenarios that could occur from construction defects that would place water into the wall.  In the Calgary scenarios I ran, if a window leaks and the water is not drained to the exterior surface of the water resistive barrier, it becomes trapped between two non-breathing layers – the exterior insulation and the interior traditional vapor retarder polyethylene (which they still use in Alberta.)  The wall can not dry and this creates the risk of growing mold. 

Building scientists and manufacturers have been preaching eliminating polyethylene from our buildings here in the U.S. for quite awhile, and promoting the use of smart vapor retarders as a solution to the problem.

As construction practices change to keep more energy in the building, some of the measures taken may unfortunately alter the traditional moisture balance of the assemblies and actually reduce our tolerance of intruding moisture. We must be very mindful of this as we continue to tighten our buildings while striving for improved indoor environmental quality.

We conclude our Be Certain events in Toronto and Vancouver later this month.  Stay tuned for how mold and moisture affect the building envelope in Ontario and British Columbia.

Lucas Hamilton is Manager, Building Science Applications for CertainTeed Corporation

Mold Awareness Month: The Five “D’s” to Controlling Mold

Lucas Hamilton

The U.S. Environmental Protection Agency (EPA) estimates that 50 percent of schools nationwide have issues linked to poor indoor air quality.  In many cases, this condition is linked to mold growth in buildings. Mold poses a serious health risk to individuals with respiratory health issues.

This has been a summer of record high temperatures and humidity across the country. This is a perfect storm for the propagation of mold.  As I discussed last year, mold is like a four legged stool.  Mold needs four things in order to grow:  food, water, oxygen and temperature between 41 and 104 degrees.  It is almost impossible to eliminate the potential for molds and mold spores to infiltrate an environment unless you control the elements that give mold it’s ‘legs.’

Controlling the moisture in and around a building is one of the best methods for maintaining a mold-free environment.  By following the five “D’s” you can protect against any opportunity for mold growth or infiltration:

De – Leak – Check for leaky roofs, walls, windows, foundations, facets and pipes regularly and repair them as soon as possible.

De – Bubble – Moisture trapped behind wallpaper paired with wallpaper glue is a perfect recipe for potential mold growth.

Dehumidify – Use dehumidifiers and air conditioners, especially in hot, humid climates to reduce moisture in the air.  Exhaust fans should be used in bathrooms and kitchens to remove moisture to the outside.

Dry – Clean and dry any damp furnishings within 24 to 48 hours to prevent mold growth.

De – Odor – Keep in mind, if you have had a leak, the first sign of mold may be musty or moldy odors. But do not sniff or touch mold.  If you suspect mold, contact a certified mold inspector.

Mold has a long history and a survival instinct that is almost unmatched in nature.  But let’s keep mold outside by making sure that moisture is managed in our buildings.

Lucas Hamilton is Manager, Building Science Applications for CertainTeed Corporation