.
Controlling Against Moisture Damage For Wall Sheathing...3 Sweaty Vents...4 Controlling Condensation In The Home...4
Controlling Against Moisture Damage For Wall Sheathing Moisture can cause many structural problems and create a very unhealthy home for your family when mold and mildew begin to form. Building a home that deals effectively with moisture requires due diligence from design to installation and on to maintenance. The home must be built in such a way as to prevent leaks which are the biggest cause of damage and it must also eliminate condensation which occurs naturally in every home. According to the APA: Good construction practices control condensation within the walls and influence the rate at which water vapor moves around and through wall system components, and mitigate the effects of humidity and temperature differentials between the inside and outside of the structure. All wall sheathing panels already contain some moisture and their moisture content will fluctuate in accordance with the moisture content of ambient air. They can also get wet when leaks occur in the building envelope. If wood panels get wet, their structural integrity is not affected. Prolonged exposure to water will cause damage over time. To prevent damage, take extra care with flashing around windows, doors, roofs, chimneys and walls. Wall sheathing panels will also get exposure to moisture when water vapor accumulates within the wall structure. This happens when air leaks carry moisture-laden air into the wall systems. You can prevent excessive water vapor damage by minimizing air leaks and reducing the conditions under which condensation occurs i.e. preventing surfaces from being colder than the dew point. There are many ways in which to prevent condensation from occurring in your walls. You can reduce air leaks by up to 60% when you utilize taller wall sheathing panels like Windstorm and TallWall. You can also utilize a vapor barrier or vapor retarders. From the APA: The proper placement of vapor retarders within a wall system will help manage the diffusion of vapor through the wall system. To determine proper vapor retarder placement and minimize moisture-related problems, the building designer must consider the interior and exterior environments, as well as the wall s thermal and water vapor permeance characteristics. The ability of vapor retarders to limit the amount of water vapor that is able to pass into the wall assembly is measured in perms. Vapor retarders with higher perm values allow more water vapor through. The vapor barrier perm value is another consideration to take into account when designing wall assemblies that will effectively deal with moisture. In section R318.1 of the 2006 IECC code, a vapor barrier of 1.0 perm or less on the side of the wall that is warm in the winter is required. This does not apply the Southern US states where hot, humid summer temperatures take precedence. 3
If you live in a climate where you need vapor barriers on different sides of the wall to correspond to the season, use OSB wall sheathing panels. OSB wall sheathing panels are smart vapor barriers as their permeance is low when relative humidity is low, but it increases as relative humidity increases in the warmer months. This allows for greater air movement which enables the wall to dry faster. Avoid creating impermeable vapor barriers on both sides of the wall as this will inhibit water that inevitably gets into the wall system from drying. From the APA: Wood structural panels are semi-permeable, and are smart vapor barriers because their permeability is low when the relative humidity is low and increases as the relative humidity increases. By increasing permeability when the wall humidity is elevated, wood structural panels help aid water vapor diffusion through exterior walls, mitigating moisture buildup in concealed spaces. This characteristic makes wood structural panels an important component of a properly designed durable exterior wall assembly. Sweaty Vents Question The walls under some of our air vents sweat in the warmer months causing water marks and streaking. Is there anything we can do about this? Answer The problem is usually caused by air filtration into your walls. Moist air from outside is leaking in near the vents and condensing. You can start by sealing all obvious gaps and cracks, but if the problem persists, it may be time to check the wall insulation. This will be costly, but it will improve your energy consumption which will go a long way to mitigating the costs. Water marks can be wiped away if they are relatively new. If they are stains, you will have to repaint. Use a primer made to cover stain to prevent streaks from showing through. Controlling Condensation In The Home For condensation to occur, all you need is moist air and a cold surface. In our homes where temperatures are controlled these conditions can occur in wall, floor and roofing systems depending on the season. Condensation is moisture that can lead to a myriad of problems from water damage to mold. With the tighter building envelopes of modern structures, this condensation problem is exacerbated as reduced air flow can prevent 4
moist areas from drying out. Luckily there are ways in which you can mitigate the conditions that lead to condensation and keep moisture out of your home. Dealing with condensation requires a threepronged approach: reducing the amount of water vapor in the air, diverting moist air out of the home with ventilation or using a vapor barrier to prevent moist air from reaching cold surfaces. Reduce Indoor Moisture Prevention is better than cure in this case, so it s best to keep moisture from the home altogether. This means that indoor pool you re thinking of including in your next build may not be the best idea. Vent dryers to the outside rather than to crawl, attic or garage spaces within the home. The same goes for other moisture producers like bathrooms and stove hoods where moisture should be carried outside rather than to other areas of the home like attics. Seal all light fixtures and plumbing to prevent moist air from entering the home or rooms that are not adequately vented. Prevent moisture from coming up through the ground with a vapor-barrier ground cover. Start by sloping the ground away from the home to move moisture away from the foundations. Homes with crawl spaces can be adequately protected with a 6mm polyethylene layer. In homes with basements, vapor-retarder barriers must be installed beneath the basement floor and on the exterior of foundation walls. Walls can be protected with a vapor barrier and the sealing of any fixtures, wiring or plumbing. Vapour barriers should be installed near the warm winter side of the wall to prevent water from penetrating the wall where it will condense and cause problems down the line. Proper Ventilation In homes with a tight building envelope, adequate ventilation is key to preventing moisture and ensuring good indoor air quality. Consult your local building codes for the ventilation requirements in your area, manufacturer s guidelines and design professional s recommendations when determining the best ventilation systems for your build. While building codes denote the minimum ventilation requirements for your area, additional ventilation may be required if you put that indoor pool in after all, if you have a sauna or hot tub, or where buildings have large kitchens or laundry facilities. In this case, refer to the recommendations of your design professional and manufacturer. Ventilation will also differ from one area of the house to the next. In attics and cathedral ceilings, a combination of ventilation and vapor retarders will help to keep moisture out. Modern homes with basements will usually come standard with a ventilation system where forced-heating systems are utilized. When heating systems (like baseboard heaters) are used which don t circulate air, separate ventilation systems will have to be considered. 5