Five Common Construction Mistakes Undermine Sales
Emphasizing practical, cost-effective building solutions that will help home builders sell more homes, the Partnership for Advancing Technology in Housing (PATH) has identified five common construction mistakes worth noting.
“The trim is on, the site cleaned up. The tools are packed away. Few feelings are more rewarding than stepping back and looking at a job well-done. But is that job really done well? Your crew may have fumbled some building basics along the way without even knowing it,” PATH writes in the current issue of Quality Matters, the e-newsletter of the NAHB Research Center's National Housing Quality Program.
PATH cites these common mistakes:
The conventional method: Run ductwork through an unconditioned attic.
Job well-done: Either run ducts in conditioned space or insulate them really well in unconditioned space.
According to the NAHB Research Center, placing ductwork in conditioned space can reduce heating and cooling loads by 20% to 35%. It also reduces overall ductwork length because supply register locations are more flexible. Wrap ductwork in conditioned spaces with R-4 insulation to prevent condensation.
Joe Gregory, purchasing manager for Bob Ward Companies, recently built the near zero energy Maximum Efficiency Home series in Baltimore. He ran a duct-blaster test to show his crew how leaky the ducts were. Now he says his subcontractors understand the level of work required to install ducts with 4% to 5% leakage rates, instead of the more typical 10%.
Floor Plan Design
The conventional method: Design the floor plan with no concern for site orientation.
Job well-done: Orient the home to take advantage of natural day lighting — and some free solar heating in the winter.
The benefits of natural lighting have been well-documented: people work better, students learn better and people are healthier in general. And designing a day-lit home needn't add expense to the project.
In all but the hottest southern climates, orient the building so the long axis runs east to west. Place a row of windows along the south wall for winter gain. Size roof overhangs to block the summer sun, but let in light and warmth from the winter sun. Cluster the main living areas along the south wall and mechanical and storage areas to the north.
Skylights are energy hogs that can make a room uncomfortably hot. Try sun tubes, or tubular skylights, to bring light into dark corners, interior rooms or even the basement without as much energy loss.
The conventional method: Put building wrap up as quickly as possible, and don't worry about tape or careful installation.
Job well-done: Follow the manufacturer's instructions.
Getting this wrong risks mold and mildew, rotting window jams and drafty walls and floors.
To get it right, overlap all seams at least 6 inches in shingle fashion so they shed water. Seal with code-approved contractor sheathing tape to make a weather-tight bond. Use proper fasteners (plastic cap nails are the best), and make inverted Y cuts (also called modified I cuts) to wrap window openings.
The conventional method: Size HVAC with a rule-of-thumb calculation.
Job well-done: Use Manual J to properly size the HVAC system.
With today’s tighter building envelopes, following the rule of thumb often results in oversized systems that cost more upfront and cost more to operate over time. Oversized systems also don’t dehumidify as well as properly sized systems because the run time is shorter, so occupants are actually paying more for discomfort.
Manual J calculations from the Air Conditioning Contractors of America (ACCA) take construction methods into account to accurately size a system. Following Manual J will take one or two hours per house and less when working with several similar houses. This added expense is almost always recouped immediately because a smaller system can be purchased.
The conventional method: Install the minimum required amount of insulation as quickly as possible.
Job well-done: Follow the U.S. Department of Energy's recommended insulation levels and installation guidelines.
Using DOE’s recommended insulation levels and installation guidelines at www.ornl.gov makes homes more comfortable, a little quieter and much less expensive to heat and cool.
How insulation is installed is just as important as how much is put in. Compression reduces insulation R-value. Research by the Oak Ridge National Laboratory shows that wall insulation that settles to create even a 5% gap reduces the effective R-value of that wall up to 50%.
Batt insulation needs to fit snugly into stud cavities and around mechanical and electrical boxes. In oddly shaped spaces or areas with notable obstructions, loose fill like blown-in cellulose may be most effective. But at least cut in the insulation to fit rather than skipping spaces or compressing it over or under boxes, piping and wiring. Spray foam costs more than most other insulations, but because it air seals while it insulates, the cost of air sealing can be eliminated and the nooks and crannies can be more easily insulated.
Insulate pipes to conserve water-heating energy, and insulate recessed can lights that penetrate the building envelope.
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