How professional builders avoid some of the most common and costly construction mistakes.

Most people judge a home by the obvious: a floor plan that’s a joy to live in, a streetscape that wows passers-by, great natural lighting, and lots of storage. The list goes on.

But some less obvious details have just as great an impact on the homeowners’ satisfaction over time. While homeowners have little control over these details, a professional builder with a sustainable business will make sure they get done right.

Some areas that require special attention from a seasoned professional are described below.

Moisture control

Mistakes here can potentially raise the chance of mold, mildew, and rot. Steve Easley, a California-based building consultant who investigates moisture problems, sees the same errors again and again. Three common ones:

• Poorly detailed horizontal valleys. One such valley is where a roof slopes into a chimney or wall. The detailing here needs to be close to perfect to keep water out.

• Lack of overhangs. In a Canadian study, 80 percent of examined homes with moisture in the walls had no roof overhang, making it easy for water to flow down the siding and into the wall.

• Improper housewrap. When water gets behind the siding, the flashing and housewrap should direct it back out before it can get into the structure. Surprisingly, one of the most common errors building science experts see in the field is a piece of flashing that laps over the one above it. Anyone with a basic grasp of gravity will understand that water dripping down the wall to this intersection will flow into the structure rather than out.

Mechanicals

Modern heating and cooling equipment is very efficient, but efficiency doesn’t guarantee comfort. Equipment must be well-sized and ducts properly sealed. Sadly, these aren’t always managed.

Some HVAC contractors still use rule-of-thumb calculations to size furnaces and air conditioners. That may have worked for old, drafty structures but with today’s tighter homes the result is often oversized equipment that costs more to buy and operate. It also leaves the home less comfortable than it could be. Smart builders hire an HVAC company that carefully calculates the home’s heating load and precisely matches the system to that load.

Another potential problem is leaky ductwork. If the leak is outside the main living area, such as in a basement duct, living and sleeping spaces won’t get the air they need. There will be comfort issues, and the equipment will have to run longer to satisfy the thermostat. If ducts run through a totally unconditioned space—for example, a hot attic in summer—leaks will create a slight vacuum that pulls unwanted outside air into the house through leaks in the floors, walls, and ceilings.

Proper insulation

When insulation is installed without enough attention to detail, the home can end up with hot and cold spots and uncomfortable drafts.

John Tooley, at Advanced Energy, a nationally known building science consultant and energy expert, says that the most common problem areas he sees are attic knee walls (short walls used to support the rafters) and vaulted ceilings. In the former the insulation usually gets installed without backing and so falls away from the wall; in the latter it’s stuffed into the ceiling cavity, leaving heat-sucking voids. “Insulation has to touch the surface of the drywall to do its job,” he points out. “That’s obviously not happening in a lot of cases.”

The common thread running through the situations above is that the builder lacked quality systems and processes to make sure insulation was installed right, mechanicals properly sized, ducts sealed, and the home protected against moisture. And if those tasks escaped scrutiny, chances are others did as well.