By NIALL MCCARRA
Just like us humans, building envelopes can experience their own cold and flu like symptoms.
Maybe this winter you can be the doctor and your building envelope the patient. Winter conditions are harsh on building envelopes, but winter is a good time to evaluate building envelope performance.
Roofs and Attics
In cold climates, roofs and attics are intended to be unconditioned spaces (i.e. conditioned air from the interior of your building should not be flowing into the attic). If
properly sealed from the interior and ventilated to the exterior, this can help to avoid issues with their performance. Symptoms that your roof and attic may be experiencing
some underlying issues during the winter could be:
- Areas of melted frost or snow on roof surfaces. This is not to be confused with windblown snow on roofs, which can expose large areas of the roofing.
- Ice dams and icicles on roof eaves.
- Icicles on underside of roof eave soffits.
- Frost build-up on the underside of the roof sheathing.
- Evidence of moisture on ceilings and around ceiling penetrations.
- Wet or stained insulation.
Heat loss and air leakage, allowing warm moist air into attic spaces, may be the underlying ailments that relate to the symptoms above.
Heat loss into attics may occur through areas of missing or displaced insulation, or the attic insulation may not be providing the required thermal resistance to reduce the heat flow from the interior conditioned spaces into the unconditioned attic spaces. Uninsulated chimney stacks or similar mechanical ducts may be another source of heat loss into attics.
Air leakage through improperly sealed ceiling penetrations such as attic hatches, bathroom fans or ceiling lights, can allow warm moist air to enter the attic spaces, causing symptoms related to condensation, such as frost on the underside of roof sheathing.
Good ventilation in attics is required to remove warm moist air and keep the temperature of the attic cool enough to reduce the risk of issues occurring with the attic and roofs. Poor ventilation can lead to accumulation of heat and moist air in the attic, possibly resulting in condensation and frost within the attic space. Insulation, air sealing and ventilation characteristics should be checked to make sure roofs and attics are performing as intended.
Windows and Doors
Windows and doors can have a significant impact on the performance of the building envelope and on the comfort of the occupants.
Condensation on the interior surfaces of windows
High interior humidity levels during colder temperatures is the most likely cause of condensation on windows. Interior humidity levels should be reviewed and adjusted as required to reduce the risk of condensation related issues, while still maintaining comfort within ones unit. As outdoor temperatures drop, so should the humidity in your unit.
Something to consider is whether or not there is enough air flow getting to the windows to remove moisture from the window surfaces. Reducing the amount of air flow getting to windows, may cause the interior surfaces of the windows to become cold enough to reach temperatures below the dew point (the temperature at which condensation can occur), which results in the formation of condensation when warm moist air comes in contact with the colder surfaces. Leaving your window treatments enough to reduce or eliminate condensation forming on your windows.
Moisture from condensation on windows could enter wall assemblies through the window frames and continued wetting of the wall assemblies could potentially cause damage to the wall framing and finishes.
If there is moisture or frost on the exterior of your windows, don’t worry, that is just outside weather conditions.
Drafty windows and doors
Drafts around window and door perimeters can allow heat loss through the windows and doors. Air leakage may occur through deteriorated or missing weather-stripping and door sweeps, and window openings or door slabs not installed flush or plumb. Sometimes ice may form around the perimeter of window and doors openings, which may cause difficulty in operating them. Review of the windows and doors could identify issues that need to be corrected. This could be as simple as an adjustment of the units or possibly replacement of weather-stripping and seals.
Condensation between window glass panes in double and triple glazed windows
A perimeter seal is installed around the triple or double glazed units to keep the cavities between glass panes air and water tight. Condensation can form between panes of glass when the perimeter seal has failed, allowing air and moisture to enter the cavities between the glass panes. This can cause condensation to occur between the panes, affecting the thermal performance of the glass units. Replacement of failed sealed glass units is required to maintain the thermal performance of windows.
Symptoms of poor building envelope performance during the winter months may help to identify underlying ailments that need to be cured. Catching the symptoms early may prevent bigger issues in the future. Contacting a Building Envelope Consultant can help with evaluating the building envelope performance and may reduce overall costs of repairing issues in the long term.
Niall McCarra is a building envelope specialist in the Edmonton office of RJC Engineers. He works on both new and existing buildings and has a good understanding of how