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The top 3 ways that water destroys our homes and buildings.


Durability in the form of preventing water damage is one of the most important characteristics for our homes and buildings. Besides destructive natural events, water and moisture is one of the most potent and damaging forces when it comes to the things we build. Western North Carolina gets lots of rain and experiences high levels of humidity for much of the year. Indoor humidity can also take its toll from the inside out.

Besides the visible damage that water can do, its the hidden damage that most homes experience and causes trouble. Most home’s water damage takes place behind the finishes and sometimes only comes to light when renovation reveals mold, decay or structural issues that have to be dealt with. Its common for hidden leaks and moisture problems to cause mold, mildew and Indoor Air Quality problems in brand new homes and go undetected for many years.

Below we break down the three main ways that water causes trouble in our dwellings.

1. Bulk Water

The most common and destructive type of water damage is a broad category that can include many sources and points of entry.  Some of the bulk water sub-categories include:

  • Water seepage though basement walls.
  • Leaks through walls at areas like doors and windows
  • Roof leaks, usually through penetrations and flashing errors
  • Plumbing leaks, sort of an outlier here but relevant

Bulk water leaks come in many forms from the rare catastrophic plumbing failure to the more common hidden leak that causes its damage over many years. Homeowner maintenance can go a long way to preventing and reducing problems. The same can be said for owners looking to build new homes: knowing the most common sources of problems and then ensuring that the building team handles them right the first time.

Bulk water intrusion is an immense subject that I will expand with further blog entries but two of the most common areas of concerns I see with new construction in our area: foundation drainage and window flashing. Iam sure any good roofer in the area could easily argue that poor roofing details are candidates for the most common problems with water damage. A blog that I mostly agree with is the 3 most common roof repairs.

roof deck decay from poor roofing details

The problem in this picture should be obvious to any experienced builder or designer; no cricket!

I write this in the middle of my own home’s renovation involving my 1920′s era basement where I have been sponging the large puddle of water that has crept in from the recent heavy rain event. I am slightly pleased by the fact that the puddle was handled by a sponge and bucket as opposed to the hose and siphon for the larger pools Ive had in the past. I am working hard to fix this problem without major excavation or installing a sump pit and pump. If only the original designer or builder had done a better job of waterproofing and/or foundation drainage..

2. Air Leaks

Uncontrolled, random air leaks are responsible for the second leading cause of water and moisture damage in our homes and buildings. Humid air will deposit its moisture on cold surfaces and over time this can add up to an amazing amount of moisture and resulting damage. This type of damage rarely reveals itself in the ways bulk water intrusion does but it can still cause serious problems behind the finished surfaces.

picture of mold on osb sheathing caused by air leak.

Attic hatchways are notorious leakage pathways.

Picture of roof sheathing with mold damage
This attic has some seriously humid air exfiltration issues.

Air leaks do most of their damage in the form of energy costs.  Reducing air infiltration and exfiltration is often pointed to as one of the most cost-effective strategies for reducing monthly, energy costs and resulting environmental impacts. Increasing comfort is another huge reason to pay close attention to this important issue.

Besides increasing comfort and reducing energy costs, stopping air leaks will reduce moisture damage to building components.  Its common for inspections and remodeling to reveal mold, decay and rot at locations that have been leaking air. Sometimes, an air leak can contribute to a bulk water leak. Bulk water is more likely to get sucked into cracks and holes that are under negative pressure from the other side. Windy conditions can easily pressurize and depressurize different areas of the house and this increases bulk water risk in windy rain events.

A good thing about this category is you can measure it. The blower door test is one of the most important diagnostic tools we have in terms of home performance. Building a home tight takes skill, care and attention to detail. Its probably safe to say that builders that are achieving good blower door test results are implementing similar best practices to resist bulk water intrusion and the next category.

Air Leaks: How They Rot Homes and Waste Money is an excellent Fine Homebuilding article by John Straube that is reproduced on the website.

#3 Vapor Diffusion

Vapor Diffusion problems can be a tricky subject to understand. There are two generalized main ways that it does damage in our climate.

  • When a moisture reservoir cladding (masonry, fiber cement siding, stucco) gets saturated with rain and the sun comes out to drive its moisture to the inside.
  • In the wintertime when exterior sheathing is cold and interior humidity is too high.

Siding materials that hold water can become a problem if not detailed correctly. Selecting the right Weather Resistive Barriers is important along with the right installation details. Rainscreens (technically required by code for brick) are an easy way to add durability and reduced maintenance to these type of exterior claddings. Look for our blog on the subject coming soon.

Amy has written some great blogs on the subject of wintertime humidity in homes. Keeping exterior sheathing warm is part of the reason for the newest building codes to require exterior insulative sheathing in cold climates which includes ours. This is a simple strategy that reduces the cold sheathing problem and boosts energy performance in a big way by providing continuous R value outside the thermal bridging of the structural framing.

As with many things in a well built home, its much easier to get right with new construction. There are MANY best practices that can be used to prevent water problems and almost ALL of them take place behind the finished surfaces. This make it tough for builders and homeowners to decide what to spend the extra money and effort on. Usually, most will do the bare minimum and depend on the local building inspector to ensure their home is up to par. This strategy can work but better results are easily achieved through careful selection of the design/building team and using third party certification like ENERGY STAR and Greenbuilt. The best results however are achieved through learning the best practices and ensuring they are implemented as much as possible.

Brian Knight

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