Oakwood Homes takes big step forward

Oakwood Homes of Denver is the largest builder along Colorado's Front Range to step up and implement high-performance design and construction in a large subdivision.

Assuming the company's homebuyers in the upcoming 500-home Overlook project in Green Valley Ranch respond positively. Oakwood would then roll out this new approach company-wide in the future.

Oakwood initiated this new direction by building six prototype hones in which they tested new practices and products. Recent testing in the first of those prototypes indicates the home performed extremely well. On the E-Star rating scale of 0 to 100, the home scored an 88 - 40 percent more efficient than Denver's energy code requirement.

Based on this and other diagnostic testing results, Oakwood plans to tweak a few elements of their building process before they start the 500-home Overlook development right down the street, But earning an 88 on their first prototype is exemplary.

Background

Oakwood's Don Carpenter, director of product development. reports that over the last three years Oakwood has explored a wide range of home energy performance issues.

"This has been on our radar screen," he said. "Our customer surveys show this is a rising concern that will stay on the top-five customer list. Affordability is an issue not just as it relates to the purchase price but also with respect to being able to pay energy bills."

One of Oakwood's first steps was to switch from fiberglass to cellulose insulation and to use insulated shallow foundations. After this start, and in the aftermath of a cycle of soaring energy prices, Oakwood President Pat Hamill decided to have an outsider evaluate the overall energy performance of the company's product.

Results from comprehensive diagnostic testing in April 2001 were more average than expected. That home earned a 79 on the 0-to-100 E-Star home energy rating scale, 5 percent less efficient than the local energy code. Still, this was a step up from their first home, hack in 1997, that scored a 75.

Not happy with these results, Oakwood brought in Brian Christensen and Paul Kriescher (Lightly Treading Design) to help redesign energy systems. A year later, Oakwood's new high-performance package is hitting on all cylinders. Says Hamill, "This will he another important statement of our commitment to quality."

New building shell features

Windows: All buyers love windows. But from an energy perspective, normal double-glazed windows are thermal holes in walls. So Oakwood upgraded to low-e glass. This step dramatically improves comfort by raising glass surfaces up to 10 degrees on cold winter nights, while rejecting much unwanted heat on sunny summer days. Other benefits include reduced fabric fading, less window condensation, downsized HVAC equipment and higher resale value. Energy savings are generally low to moderate, depending on building/window orientation.

Walls: Oakwood switched their Overlook project to advanced fuming. Using 2-by-6-inch studs at 24-inch centers increased their cellulose-insulated wall's R-value by over 50 percent. This step results in substantial energy savings, especially in two-story models, while optimizing comfort. Oakwood's use of dense-packed cellulose in floors above garages is a sure-fire way to minimize comfort problems in the rooms above.

Tightness: The detailed demonstration rating last year showed an average figure for house tightness. But in the first prototype home, air leakage was cut by more than 50 percent compared to the average new home. This demands attention to detail during design, material specification, construction and follow-up inspection.

Air quality decisions

Some builders and buyers worry that tightening a house reduces indoor air quality. Without wading too far into the building science, the short answer is "yes and no." What house tightening does, in addition to saving energy and improving comfort, is improve the effectiveness of a home's controlled mechanical ventilation system.

People seem barely aware that the "V" in HVAC stands for ventilation. Kitchens and baths need spot ventilation to reduce excess humidity and the buildup of indoor air pollution. Houses need dilution ventilation to remove low-level contaminants throughout the home. Unfortunately, in most houses ventilation is random or accidental; sometimes you have it, very often you don't. Noisy bath fans aren't run long enough, and most kitchens don't have any exhaust fan.

Oakwood's new homes in Overlook each include a mechanical ventilation system that brings in fresh air on a 24/7 basis. The amount and timing of delivered fresh air is controllable. This clearly improves indoor air quality.

Detailed performance testing along the Front Range has highlighted a substantial indoor air quality concern: the potential for conventionally vented water heaters to spill exhaust gases into the rooms where they are located. Once re-burned in the water heater, those gases can gene ate unhealthy levels of indoor carbon monoxide. One of the few effective ways to beat this problem is to install a much safer water heater. one that uses a fan for power-venting exhaust gases to the outdoors. That's exactly what Oakwood elected to do in their Overlook subdivision. Smart move.

Other HVAC issues

A systems-built. high-performance home allows a builder to downsize their heating and cooling equipment. Is this a shortcut in quality? Quite the opposite.

Yes, downsizing HVAC equipment (think of it as "right-sizing") saves money, especially when air-conditioners are downsized. But more importantly, right-sizing improves comfort, increases equipment lifetimes, decreases energy bills, cuts down on noise and reduces initial costs. If you're keeping score, that's a 5-0 shutout.

How do you know when equipment is right-sized? When your HVAC contractor ignores traditional "rules of thumb" and uses calculation tools like Manual J for selecting equipment size. Eastside Heating and Air Conditioning, one of Oakwood's HVAC contractors, worked with Kriescher and Christensen to determine proper equipment sizing for the new Oakwood models.

"In one of the larger homes, we're putting in a 45,000 Btu furnace upstairs and a 60,000 Btu unit downstairs where we would normally install two 100.000 Btu units." said Eastside's Paul Kampbell. In those same homes, Kampbell reports that right-sizing the air conditioning equipment, based on Oakwood's upgraded energy features, eliminates the need for between three and tour tons of air conditioning.

Oakwood also upgraded to furnaces with 90-plus percent efficiency ratings. While this measure increases initial costs, it cuts heating bills by roughly 15 percent. thus paying for itself over the appliance's lifetime.

Tuning, testing and education

When Kriescher reported his very promising initial test results to Oakwood, they were thrilled with the higher performance but then immediately focused on what they could do differently to make further improvements.

"They were a bit dismayed at the fact that the HVAC system wasn't delivering the calculated amount of air to all rooms in the first prototype," he said. That's what building a prototype home is all about: trying new approaches and tuning them up until the details all work. Kriescher and Kampbell are already in the process of figuring out the tweaks needed for the HVAC system to perform as specified.

Is this an unusual situation? Not at all. Consider that two other Denver-area builders who switched over to high-performance design and construction during the last year have encountered glitches with their HVAC system performance. The root problem: because nearly all residential HVAC systems are installed without an on-paper design process and aren't tested after installation, conditioning is random. No one really knows how well they're working. The benefit of building prototype homes and then performing detailed tests is that they offer opportunities to test new practices and do some fine-tuning.

During the blower-door house tightness test. Kriescher reports that the only location he identified where substantial air was leaking flowed between the concrete wall and the mud sill. In the Overlook homes, Oakwood indicates that materials choices and applications will be modified to curt down on this typical trouble spot.

"There's a steep learning curve with this new approach," said Carpenter. "We had to incorporate good HVAC design from the get-go, which is new to the industry and required some modification of our plans. Now we're learning a lot from all the performance testing. Once we validate that our buyers are getting what we're paying for, we'll cut back some on our testing. Eventually, this new approach will become our standard. It will separate us from our competition. And the economies of the way we do business will help us keep our costs in line."

Because the systems-built, high-performance approach is relatively new to the industry, Oakwood plans to provide extensive training to their field and sales staff to make sure everyone is on hoard with the new objectives and committed to achieving them as efficiently as possible. Even the company's structural engineers and the code jurisdictions with whom they work need some education.

Big benefits

Oakwood's slogan - "More house, less money" - refers to an edge they enjoy in the marketplace due to their rationalized design. scheduling and building systems. Now they're adding high performance. Yes, Oakwood's new package adds to their costs. But the benefits should substantially outweigh the cost bump. And the energy savings should cover the slightly higher initial mortgage.

Buyers who pick up a home with Oakwood's new high-performance package should experience improved comfort, thanks to the better-insulated shell and deliberately designed HVAC system. Better indoor air quality occurs when a controllable ventilation system is installed. Choosing state-of-the-art water heaters will improve combustion safety. Tight ductwork will increase each home's durability. Energy bills will drop.

The bottom-line element of this new high-performance approach for Oakwood: "We know we're doing the right thing for our customers," said Carpenter.

Steve Andrews consults with builders for E-Star Colorado and writes on energy issues (sbandrews@att.net). E-Star (www.e-star.com), is a nonprofit home energy rating system that works with both new and existing homes statewide.

2008 Built Green Colorado

Home Builders Association of Metro Denver, 9033 E. Easter Place, Suite 200, Centennial, CO 80112
(303) 778-1400 fax: (303) 733-9440  info@builtgreen.org

Last Updated: 10/05/2007