When asked for advice about the easiest way to tear down an old wooden barn, the weathered Vermont farmer offered that “it’s simple – just cut an 18-inch hole in the roof and stand back!” He knew that water is the worst enemy of any wood-framed building and that rain and snow would make short work of the barn demolition.
One of the principal intentions of today’s green building movement is to improve durability, thereby extending the life spans of both new and existing homes. One of the simplest ways to prevent the waste of construction materials is to increase the service life of buildings. Far more homes die an early death from water intrusion and the resulting moldy decomposition than from any other cause.
The construction industry has somewhat of a checkered past as it relates to home durability – some homes last a long time, others not so much. It might be easy to say that homes were built better 100 years ago, but the truth is that the bad examples of building technique from that era are already in the landfill, victims of poor water management or construction. Mold has become more of an issue in the last 20 to 30 years because we have been building more-airtight homes that eventually developed problems from misapplied building science or poor water-sealing and could not dry like older draftier homes do. And it wasn’t just builders – the building codes and enforcement officials also suffered from incomplete knowledge. We have learned a lot from these failures however, and the prospective future longevity of our homes is looking better all the time.
There are really only a couple of ways that moisture invades the structural shell of homes. The first, most direct way is by rain and snowmelt (bulk water) leaking into our buildings at roof penetrations, roof-to-wall intersections, window openings, siding penetrations, chimneys, ice dams backing up, etc. There are lots of ways that homes leak water and they all lead to the same thing – terminal rot. Since these are the most obvious ways that water enters our homes, they are also the simplest to avoid with good flashing and siding techniques by conscientious builders who understand the subtleties of water management.
The other, less apparent way that moisture ruins our buildings is from vapor leaking into the building shell and condensing in the wall or roof cavities. This phenomenon is all too common in a cold climate like we have here in Northwest Montana. Each and every household creates a warm, relatively humid indoor environment through the everyday activities of cooking, breathing, showering, watering plants, washing the dishes, ground evaporation at crawlspaces, etc. This warm vapor quite naturally wants to escape to the outside in the winter where the air is colder and drier. So, as this vapor leaks out with the indoor air wherever it can and reaches a surface cold enough to cause condensation, it morphs into water that starts doing what water always does in contact with wood – grows some fungus and starts the decomposition process. If this occurs, it is usually on the inside face of the exterior wall or roof plywood where it is destructively invisible. We have all seen rotting logs on the forest floor? Same process – just in the walls or roof of your home – not a pretty picture. Green builders avoid this problem by managing indoor moisture with mechanical ventilation and better air-sealing of wall and roof penetrations.
The other downside to this water damage is that the subsequent mold growth can undeniably create poor indoor air quality and genuine health issues for the occupants. Green builders, being committed to durability and health, have many reasons to manage water and vapor in their homes and now have the science to do so. This focus adds almost no cost to home construction but carries benefits for both the building and its occupants that extend far into the future.
Len Ford is president of Ford Construction Corp., a certified green builder, and chairman of the FBA Green Build committee.