Moisture and water vapor move in and out of a house in three ways: with air currents; by diffusion through materials; and by heat transfer. Of these three, air movement accounts for more than 98% of all water vapor movement in building cavities. Air naturally moves from a high-pressure area to a lower one by the easiest path possible-generally, through any available hole or crack in the building envelope. Moisture transfer by aircurrents is very fast-in the range of several hundred cubic feet of air per minute.Thus, to control air movement, a house should have any unintended air paths thoroughly and permanently sealed.
The laws of physics govern how moist air reacts within various temperature conditions. The study of the properties of moist air is technically referred to as “psychrometrics.” A psychrometric chart is used by professionals to determine at what temperature and moisture concentration water vapor begins to condense. This is called the “dew point.” By learning how to determine the dew point, you will better understand how to diagnose moisture problems in a house.Ventilating roofs in hot and humid conditions may add (rather than remove) moisture from attics and enclosed roof spaces. However, not ventilating roofs may void the asphalt-composition roofing manufacturer’s warranty, and slightly decrease the life expectancy of the roofing material due to increased temperature of the roof’s surface.
Recommended minimum widths for roof overhangs for one- and two-story wood-frame buildings are typically 12to 24 inches. For taller structures, larger roof overhangs are desirable. Alternatively, porch roofs and upperfloor overhangs can be used to protect lower-story walls.
Some jurisdictions do not regulate roof overhangs. Common problems with guttering are associated with installation and maintenance. Home inspectors can check ifproperly sized materials are being used, if guttering is appropriately sloped toward adequately sized downspouts,and if discharge is directed away from the building’s perimeter. Discharging water at inside building cornersshould be avoided. Some local storm water requirements may require special infiltration or filtration treatmentsof roof runoff.
The installation of even the most weather-resistant wall envelope system on a house does not diminish the need or proper installation, particularly with regard to flashing details at penetrations. In addition, the use of roof overhangs provides performance benefits for all cladding systems by reducing the moisture load experienced over time, and by allowing greater opportunities for walls to dry in the event of periodic wetting due to wind-driven rain. The life expectancy of various siding materials may vary widely, from 10 to as much as 100 years or more, depending on type of material, climate exposure, maintenance, and other factors.
Face-Sealed: This type of WRE relies exclusively on the ability of the outer surface of the wall and joints around penetrations to deflect water and prevent it from penetrating the wall surface. If a defect in the wall surface or joint detailing (such as caulk) exists or occurs over time, then water will penetrate and potentially accumulate in the wall, causing damage to any moisture-sensitive materials within the assembly. One example of this type of system is known as conventional or barrier EIFS (exterior insulation finish system). However, building standards only allow the use of a new type of drainable EIFS (i.e., drained cavity) on residential construction.
Assessing your buildings exposure can determine the amount of protection required. The terrain surrounding a building impacts its exposure to wind-driven rain. The ratio of roof overhang width to the height of the protected wall below also alters the exposure of a building to weather and wind-driven rain. Long roof overhangs relative towall height effectively reduce the exposure. Similarly, increased shielding of the site against wind tends to reduce the effects of climate. Understanding the exposure in this manner can guide inspections of flashing details, the potential benefits of having greater overhangs installed, etc.
Many performance problems with windows and doors are related to installation issues. Installation directionsincluded with window and door units should be followed carefully. Home inspectors are not required to confirm compliance with a manufacturer’s recommendations. However, knowing the general guidelines and techniques for proper installation of windows and doors will assist the inspector in recognizing installation problems that may promote moisture intrusion.
Having your home inspected by a Certified Building Code Official will identify most common moisture issues and the Barrie Home Inspector is available to help identify and correct moisture issues in your home.
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