Building for Durability: How to Recognize and Avoid the Most Common Mistakes
It can be difficult to think about long-term durability when building a new home, because every material is new and seems durable at that time. But what would happen if you left each material outside, exposed to the sun, rain, high winds and other elements over years or decades? How long would those materials continue to be useful? Or would the home be a nightmare to maintain? The reality is that new, apparently durable materials can still be “exposed” and subject to damage if they’re not installed properly or protected adequately. This article describes the most common durability mistakes in residential construction, their causes, and how to avoid them.
By far the most common and alarming mistakes in residential construction relate to moisture management. Over the life of a home, any event that introduces water into building cavities or that traps moisture will ultimately lead to rotting wood, mold and potential health issues for the occupants. Attention to detail is crucial in any effort to prevent bulk water intrusion into the building assembly or to provide a means for water vapor to “dry out” of building materials. There are many ways that moisture can get in and several ways that it can get trapped and unable to get back out. Each of these mistakes is cause for concern.
Poor building design: Deep roof overhangs and covered porches create a sort of umbrella over windows, doors and walls, reducing their direct exposure to rain and potential leaks. These are also excellent shading devices, keeping direct sun off those assemblies, which reduces UV degradation while improving energy efficiency. Windows and doors not in close proximity to roof overhangs (like on the first floor of a two-story home) extend an open invitation for water to come in. Adding a shed roof such as a covered patio or awnings directly over each opening provides the needed protection.
Complex designs also significantly increase durability risks. Every time the design turns a corner on an exterior wall or features a three-dimensional assembly such as a cantilevered room or boxed-out window, the additional intersection of planes provides more opportunities for water to get in. Chopped-up roof lines with lots of peaks and valleys also mean more potential leak sites.
Lack of sealing: The most common cause of water damage in buildings is the failure to seal all the places that water can get in. There are literally hundreds of specific products made for every flashing and sealing detail. Unfortunately, many builders don’t make the effort to find the right one for each application. Instead, they try a “one size fits all” approach, using tapes, caulks or flashings that were never intended for all of those uses. Or they choose inexpensive products that won’t last. An area may look like it’s sealed up, but over time as the sealing product disintegrates, the home will become vulnerable to water intrusion. This is why there are specialty flashings that keep water from getting under the bottom edges of different assemblies and special connectors that prevent moisture from wicking upward. Failure to adequately detail building specifications can be an open invitation for less than acceptable materials and methods.
Worse than poor sealing of penetrations, vents and building-assembly connections is no sealing at all. Unsealed areas under negative pressure can actually suck water into assemblies that are otherwise not exposed to direct water intrusion. It’s unfortunate to see a builder touting high-performance materials like spray foam, but then failing to seal up wiring and vent penetrations that run through that product and the wall or roof assembly. It’s like having multiple holes in a raincoat.
Improper installation: It’s not just the using the right products that results in durability; it’s also making sure that they are installed properly. All wall- and roof-assembly drainage materials should be overlapped shingle-style, with installation starting at the bottom and working its way up, so each layer is laid on top of the one below and water doesn’t have an opportunity to get behind the layers as it runs down. For example, when installing flashing around windows and doors, the bottom flashing should be installed first, followed by the sides and finally the top, sealing the house wrap in the same top-down drainage pattern. Improperly trained installation crews may not know to follow these best practices, and a lack of quality control supervision will allow their mistakes to go unnoticed.
In the wall assembly itself, the outside of the wall frame (stud cavities) is typically wrapped in sheathing and then a house-wrap fabric, or some hybrid combination of the two. In Austin’s hot and humid climate, the wrap should be vapor-permeable, allowing any moisture vapor that finds its way into the wall assembly to dry back outward. On the outside of the wrap, there should be a clear, half-inch airspace between the wrap and the façade. A brick, stone or siding façade is porous, so water that gets behind it into the airspace will need to run down the wrap and out the bottom. Unfortunately, brick and stone masons can leave mortar clogging the airspace if this detail is not checked.
Wall assemblies also should be able to dry to the inside of the house, as water vapor from cooking and bathing can permeate the drywall and get into the walls. This is why kitchen and bath vents should be ducted to exhaust moisture to the outside. It is also why it is never a good idea to install vinyl wallcovering on the inside of exterior walls.
Pest damage is most likely to occur in areas with moderate to heavy risk of termite infestation, but it can happen anywhere. Even in an area with no history of termite damage, a colony could appear anytime over the years. The same is true for carpenter ants. To guard against long-term problems, it is best to treat the wood frame of the building during construction (before the insulation is installed, at least three feet up from the foundation) with borate. This is a natural, non-toxic, and permanent treatment.
Subterranean termites, which can enter into the home through plumbing penetrations in the foundation, also pose a threat. Very fine metal-mesh products can be installed around those penetrations as a preventive measure. There are also exterior barriers that can be installed around the outside of the foundation to reduce this risk. Special termite screens for weep holes are ideal for allowing wall water drainage while still preventing termites.
To keep rodents out of the attic, it’s vital to seal up even the tiniest access points into the roof assembly. A mouse can squeeze through a quarter-inch opening and, once inside, chew away at wood and wiring and deposit unpleasant and unhealthy waste.
At least six inches of exposed foundation (after final grade) is necessary to allow for annual visual inspections to note any termite tunnels that form and address them before they do much damage. Pushing soil and landscape mulch up near the top of the foundation line invites insects and moisture from even a quick rain up into the wall assembly. It’s also a good idea to keep all landscape plants three feet from the foundation, so they don’t serve as a bridge for pests to find their way into the home.
Poor site development strategy – or, worse, no site development strategy at all – can result in stormwater damage. Most sites have grade changes that cause water to run across the lot in a certain direction. If that direction is toward the house, water should be directed away from the structure so that heavy rain doesn’t damage the foundation or send a river of water into the house. (If one side of a house receives more water than the other, it can eventually cause foundation cracking, particularly with clay soils.) Gutter downspouts can be positioned to aid in directing water away from the foundation. On a flat lot, water should be drained away from the house in all directions.
Wind and Fire Risk
To reduce the risk of threats to durability from wind and fire, International Residential Codes (IRC) require the use of building (structural) connectors rated for wind loads by region. Unfortunately, when building happens outside of a municipal jurisdiction that performs building code inspections, builders or framers may not follow this requirement. If this is a possibility, an independent third-party inspector can perform a frame walk to ensure the appropriate connectors have been installed and structural bracing methods applied. If the house has not been built and braced properly, and a significant wind event occurs, the homeowner may end up without a home.
In any area with a history of tornado activity or high fire risk during extended droughts, it’s well worth considering building materials and methods that are known to offer superior resistance to these events. Fiber-cement siding, brick facades and stone facades all hold up better than other materials against wind and fire exposure, as does metal roofing.
A major cause of residential fires in a wildfire is embers being sucked into ventilated attics by the shear wind force created by the design of the vented assembly. In these cases, the fire starts inside the attic, as opposed to the home being engulfed by flames from the outside. An unvented attic (a sealed assembly insulated at the rafters) will prevent wind-dispersed embers from entering the attic through soffit vents from a remote fire.
Recognize, too, that materials and installation methods that offer greater long-term durability may cost a little more. A low bid provides no assurance of quality, and unless specifications are clearly defined for the materials and installation methods, multiple bids won’t present the same value. Think about how much poor-quality materials and workmanship could end up costing in maintenance in the long run. It is important for hedging against increasing repair and replacement costs over time, important for resale value, and important for your long-term total cost of ownership and peace of mind.
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