Frost-protected shallow foundations. In-line framing. Single-layer subfloors. These techniques can save on your hard costs, at the same time benefiting generations of homeowners. Here's how to shave costs without sacrificing quality or energy efficiency.
Analysis of the demographic trends likely to impact housing in the next decade makes a strong case for continued growth in the housing industry. In fact, the NAHB has predicted that housing starts may hit the two-million-per-year mark in this decade, due to immigration, smaller families, and removal of existing housing stock.
According to a report recently published in the Forest Products Journal, the way those homes are built is rapidly changing. And for small- and mid-sized builders, getting in on that change is no longer optional. Why? Because fewer skilled tradespeople are entering the job pipeline, and building codes have changed. What's more, the public has become much more savvy about home energy efficiency--and more litigious.
Add to those trends the growing cost of construction waste disposal, the enormous need for affordable housing (with affordable energy bills), and the approaching thunder of big builders pulverizing smaller builders, and you see where things are headed. Smaller builders face a tough mandate: Streamline operations to cut material and labor costs, and at the same time improve energy efficiency and reduce waste--yet leave no weak points in construction quality.
The long haul
Fortunately, pulling that off isn't impossible. Most of the products, research, and know-how can be readily obtained. Many systems previously relegated to the "fringe" have gone mainstream and found a place of honor in the new International Residential Code (IRC), including structural insulated panels and frost-protected shallow foundations.
But before deciding to dive headfirst into optimized building systems and products, largely ignored research points out some major blind spots in the way homes are constructed. Before you can offer a home that genuinely costs less to build, yet lasts as long or longer than standard construction, you may want to check out a study done by the University of Michigan (see Web link at end of feature).
In the study, researchers looked at the total life-cycle mass (raw materials used) plus the energy needs (for heating, cooling, etc.) of a new 2,450-square-foot home. They estimated its life-span at 50 years. Their calculations include not just initial construction materials, but maintenance, improvement, and--most importantly--lifelong energy usage. The figures they arrived at make a powerful statement about which efficiencies should come first.
For example, their "standard" home would require a life-cycle mass of 305.9 metric tons of materials (concrete, asphalt shingles, lumber, etc.) over its 50-year life-span. Along with that hefty footprint comes a massive energy bill--due long after construction is complete. In fact, only 6.1 percent of a home's total embodied energy, that is, the energy required to produce and maintain the structure, is accounted for in the manufacture of its raw materials. Another 93.7 percent is consumed in heating, cooling, and lighting the house for years after the builder is gone. And 0.2 percent is used in the end-of-life phase, disposing of the old building.
The implications: Product choices and construction methods at the building phase can drastically change how much a home costs its owners (and society) for decades. But fixing the problem is complex. As you trim hard costs and improve energy efficiency during construction, durability must remain constant--or improve. That should be the starting point for any "optimization" of the building process.
To begin the process of optimization, take a look at the Michigan study, which ranks homes based on their life-cycle impact. At the top of the list (requiring the most resources): foundation/basement walls--followed by interior walls and roofs. These systems have the highest initial cost, coupled with the greatest impact on long-term energy costs.
But alternatives do exist--and builders are testing new ground. Take foundations, for example: Along with the rising popularity of frost-protected and tilt-up concrete foundations, pressure-treated wood foundations have enjoyed a resurgence. According to Kathy Kaake, with the Southern Forest Products Association (SFPA), most of the calls her organization receives lately have to do with permanent wood foundations--despite recent controversy over the use of copper chromium arsenic (CCA)- treated products.
"The EPA has ruled that CCA can still be used in permanent foundations," Kaake notes. Her colleague, Dave Mason, director of treated products with the SFPA, adds that alternative wood treatments such as alkaline copper quaternary (ACQ) can be used instead of CCA-treated wood, with similar durability.
"There are about 350,000 homes with treated wood foundations in the United States now, with about 10,000 more being built each year," Mason says. "Most distributors offer a 75-year warranty against deterioration of the wood. But it's really homeowners who are driving it. They like the comfort of a basement built with wood. You don't get the dampness you do with concrete walls. From the builder's perspective, it's easy. Their framers can build the walls even in winter, and they don't have to wait for concrete to cure."
So in selecting the cost-cutting materials and techniques for this special how-to article, we targeted those parts of the house most aggressively. These proven techniques have been around for many years but haven't yet become standard operating procedure, for various reasons, including learning curves for crews, lack of pre-planning by builders, and code ambiguities.
But most of these objections have since been addressed. Now might be the time. According to the NAHB Research Center, by using these techniques you can save as much as 12 percent on your overall construction costs.
Designing by numbers
As you plan preliminary layouts and elevations for floors and walls, think in 2-foot modules. This size makes best use of standard-sized building materials: plywood, softwood lumber, rigid foam insulation, etc. In addition, for overall floor space design, keep in mind that the most efficient rectangle is a square, because it offers the greatest amount of floor space per linear foot of exterior wall.
Treated-wood foundations have gained in popularity lately, in part because many state building codes now require insulated foundations. The system can be built with no concrete (appealing to builders in winter climates), using galvanized fasteners above grade and stainless fasteners below the ground. The big payoff: The wall can be insulated easily with fiberglass or cellulose, without need for furring strips. And the wood won't wick water the way concrete does. Treated-wood foundations require the same careful attention to drainage as concrete walls but typically have no footers other than a bed of gravel.
All framing plans should be drawn up prior to construction and designed so that load-bearing members align atop one another. The biggest perk from this type of in-line or "stack" framing: more room for insulation. Most experts recommend use of 24-inches-on-center 2x6 wall framing, a system with better insulated value and strength than a comparable 16-inches-on-center wall (according to the Forest Products Laboratory). Careful planning allows windows to be placed between studs, and glued plywood box headers can also be added to allow for insulation above windows and doors. Gluing sheathing and drywall to walls also adds significant shear strength and, ultimately, durability to walls.
For more efficient use of lumber in floors, off-center staggered joists fastened with metal truss plates may be acceptable if breaks are carefully alternated along the carrying girder (which can be wood or steel). Alternately, specify engineered I-joists for longer spans. If in-line framing is used, band joists may be reduced to a 1-inch nominal thickness. Of even greater potential impact, with careful fastening and use of premium adhesives, a single layer of subfloor may suffice if the finished floor will include wall-to-wall carpet or resilient flooring. The subfloor should be 3/4-inch-thick, tongue-and-groove oriented strand board or structural panels, with joists spaced a maximum of 2 foot on center.
Source: Original illustrations from "Cost Effective Home Building," NAHB Research Center. to order a hard copy, call 800-223-2665.
Short and sweet
Frost-protected shallow foundations have now become part of the IRC and have been field tested for more than a decade. For effective installation, drainage away from the house is critical. The R-value of the rigid foam insulation required will vary by region. Roofs should be guttered, and final slope away from the building should be at least 1/2-inch per foot. Flashing the transition from wall framing to foundation insulation is also critical, and all above-grade insulation should be protected. Both HUD and the NAHB Research Center publish thorough design guides on the process (see Web link).
Corner framing has always been one of the biggest wood wasters (and labor makers) of conventional stick framing. Some builders consider the use of drywall clips in corners a sign of poor quality. But two-piece (as opposed to the typical three-piece) corners can create a sturdy bond, provided one wall is screwed securely to the corner and the other "floats" against drywall clips. The system, however, does more than save lumber. It allows corners to be properly insulated, improving wall system efficiency for the life-span of the building.
A recent study by the Manufactured Housing Research Alliance, based in New York, found that tradespeople (at least those who work in the factory) have mixed feelings about the role of adhesives in home construction.
But manufacturers (in the same report) suggested that misuse of the products could negatively skew how well they work. For example, workers may use excessive amounts of sealant, creating a mess and a weaker bond. Many building firms, sealant makers note, are so focused on "raw, in-the-door adhesive price" that they tend to use lower-quality products--and don't acknowledge big differences in durability and product quality.
Premium products, they argue, cost more for a reason--because the chemical components add tremendous value. They also point out that the fast track nature of a factory production line may not give adhesives time to set fully. For site builders, especially smaller firms, this issue would be unlikely to make waves.
For the layperson, the complexities of adhesive chemistry may seem out of reach, but at least one Web site includes an interactive matchmaker, which allows you to name the two materials you plan to stick together, then get a reading on the best type of adhesive. Check out the Techcenter adhesion guide, available through the BUILDER Web link below left.
Learn more about markets featured in this article: Ann Arbor, MI.