Article No: 258

2009-06-08 12:01:16

photography by Thomas McConnell
Building a “green” concrete house these days allows the homeowner several possible construction methods, all producing a dramatic home that is the most energy-efficient available, well-insulated not only from weather extremes but also from noise and damage from insects, and that will stand up for a lifetime to hurricanes, tornadoes, fires and floods. And today’s sustainable concrete homes are easy to build, go up quickly and can easily earn green ratings from national, state and local organizations.

Renovating a nearly 60-year-old home that is concrete from the bottom to the top with the highest-end modern amenities is a challenge at best. But then when the homeowners want the renovated house to qualify for an Austin, Texas, Energy Green Building Program Five-Star-rating, the challenge becomes, in a word from the construction project manager, “interesting.”

A Five-Star-rating is the highest rating that can be attained in the Austin Energy Green Building Program, and it is seldom achieved on a remodel – especially the challenge of remodeling a home with 8-inch concrete walls, floors and a roof that was poured in the 1950s. Austin Energy Green Building Program rates the HVAC, windows, doors, appliances and electrical fixtures, and homes must be certified and tested by a Home Energy Rating System (HERS) certified home rater.

Possibly a Stenger house

The house being renovated, owned by John Barton and Diane Stewart, is believed to possibly be an Authur Dallas “AD”  Stenger home, the work of a noted Austin architect who was a disciple of Frank Lloyd Wright and who built more than 100 mid-century modern homes in Austin, many of which are now considered to be some of Austin’s most unique homes of the post-war period of the 1940s and 1950s.

Stenger was a friend of Austin-based radio host and national author John Henry Faulk. In 1957 when Faulk was blacklisted as a communist in the McCarthy era, Stenger built and financed a home for Faulk, knowing his friend was buried in legal fees.

He took his other clients’ financial situations into account as well, helping offset furniture costs with built-ins in every room, and pricing his houses between $18,000 and $22,000, although today they can range from $400,000 to $600,000. This remodeled house went on the market when it was completed at $493,874.

The remodel was done by CG&S Design–Build, an Austin construction company. One of the subcontractors on the remodel who was installing countertops said he remembered the house to have been originally designed by Stenger.
Riley Tripp, an architect and professor at the University of Texas at Austin, has become an expert on AD Stenger houses, cataloguing and profiling each architectural treasure, and he is hoping to publish a book about Stenger’s influences on Austin architecture. Tripp, who grew up in a Stenger house, said he is studying this house at 403 Vale St., but has not yet determined if it is a Stenger or not.

“He built several homes in this area of Austin and it certainly reflects a Stenger style, but I can’t yet say if it is or is not,” Riley said. When the spring semester ends, he will visit the house and complete his research.

Riley said a Stenger house will stand out with signature low-peaked roofs, and clad with concrete, wood, rock and other organic materials. Stenger also used rock and stone quarried from the home site as siding or built into the fireplace, helping the house fit easily within its surroundings. He also had a love for long, low-slung fireplaces reminiscent of 1950s lounges, so every home he built included a wood-burning fireplace.

Stenger houses also have many of the amenities that Austin’s big modern building boom still cherish with walls of windows and clerestory windows hanging just below the exposed roofline; tinted concrete floors; and built-in furniture such as bedroom, bath and living room dressers, bookcases and storage areas. He also used the organic building theory of “bringing the outside in,” by running exterior stonework through the house’s interior.

Though Barton Hills where many of his homes were built was featured as “the world’s largest air-conditioned subdivision” in the 1956 Parade of Homes, Stenger didn’t build his homes with central air. Instead, he built large windows to catch morning light, and not the hot mid-afternoon sun; and a floor plan to allow for a breezy pass-through ventilation when the windows were opened.

Tripp also said he has not come across a Stenger house made entirely of concrete, but he said Stenger liked to use concrete as decorative work on both the exterior and interior. “He very well may have tried concrete construction as he liked to use different building methods.”

The renovation project
Built in the early 1950s, this 3,214-square-foot home was constructed almost entirely of concrete, including exterior and some interior walls, the floor and roof. CG&S Project Manager Jim Venable said the owners wanted to rearrange several of the rooms and modify the existing floor plan, add a new master bath, and upgrade the finishes throughout the house. After meeting with Austin designer Mark Lind, they embraced the idea of building green and wanted to get the highest possible Five-Star rating.

Venable said that it’s not difficult to get a Five-Star rating for a new green-constructed home, but getting it on a remodel is more of a challenge and doing it on a concrete remodel was “interesting.”

“I’ve never seen a house built like this one before,” he said. “It must have taken this guy a long time to frame this up and build. Even though the house is more than 50 years old, everything has stayed pretty straight and all the walls are plum.” Despite Austin’s location on the Balcones fault, the house has no cracks.

The house slopes up a hill from the front to the back, so the front third of the house is on pier-and-beam with a crawl space, and the back of the house is on a slab.

“It was built in three separate sections,” Venable explained. “It’s got two beams that run back-to-front of the house that holds up the roof and naturally divides the house into thirds. Facing the house from the street, the living room is up front in the center of the house with a Stenger-style sun room behind it. The kitchen and family room are in the right third,  and a bedroom wing is on the left third. Most of the work was done in the bedroom wing.

The two substantial concrete beams span about 22 feet from exterior walls front-to-back on the inside of the house and they are about 8 inches wide by 14 inches thick. These beams hold up the roof and form those three natural divisions. The 8-inch-thick concrete roof sits on top of the beams and the exterior walls, completing the concrete envelope.

“There were a couple of chases cut into the roof beams to get wiring down, but nothing we could use, so we had to drill a lot of holes in the roof for electrical wiring and cabling,” he said. “All the interior walls that we built were non-load bearing because the roof beams are supporting the roof, creating the open expanses.

“The 8-inch-thick concrete roof, reinforced with steel that runs both directions, was originally built with only one roof drain in the far corner of the carport area,” he said identifying a problem area. “Because the roof drain came in the corner, the eave actually tapers, and it created a swimming pool effect on the roof causing the roof to hold water that would eventually drain.

“We added another drain on the bedroom side and took it all the way down through the back wall of the office area and out the front and then trenched out all the way to the street.”

Even though the concrete roof was originally built with 42-inch overhangs in the Stenger style, it fell short of current energy codes. In order to improve its energy efficiency, rigid 5.25-inch insulation was added to the existing roof, replacing the original crumbing foam insulation.

“We built some little valleys into that insulation so water on the roof would flow toward the new drain, and we used a membrane on top of that,” the project manager explained. So there’s really good insulation on the roof now, and water no longer stands.

Because most of the real concrete work was done with the original build, the concrete work in the remodel consisted mostly of removing some of it. That work went to Austin concrete cutter Penhall Co., as their big saws removed concrete from the roof, the eaves and interior walls. The roof’s 42-inch concrete eaves had to be notched in two places to accommodate a 239-square-foot addition to the master bath.

Venable said before cutting into the roof to place air conditioning, drilling holes or removing walls, Penhall had to x-ray the entire structure to determine the location and spacing of the rebar. CG&S didn’t want to cut the reinforcing steel because they didn’t want to compromise the strength of the concrete.
Working inside
To create a transition from the front porch into the living room, the original open front porch was converted into an enclosed entry vestibule using a commercial glass curtain wall system. The area used as a master suite by the owners was returned to its original purpose as a family room.

The existing fireplace was reclad in a stacked veneer of cultured stone in Stenger style, and the cantilevered hearth constructed from a horizontal slab of marble supports walnut shelving separated by metal stand-offs. Custom cabinetry on the other side of the fireplace houses the entertainment components in a freestanding media cabinet supported by a single steel post.

The renovated master suite, now back in its original location, has been enlarged by the addition of a new master bath. The master bedroom features a built-in platform bed and drawers, with freestanding shelves supported by metal stand-offs like the ones by the fireplace, and all cabinets are of stained walnut. A walk-in closet and built-in storage cabinets line the hallway connecting the bedroom to the master bath.

The concrete roof overhang had to be cut for the new bath and a 4-foot by 16-foot slab poured for that addition.
“Penhall cut two notches out of the eaves, each weighing about a ton,” Venable said. “We had a forklift there to support the concrete panel being removed and then lower it to the ground and remove it.”

He said the bathroom addition walls are constructed on three sides by floor-to-ceiling glass block walls similar to those used to enclose the former front porch. High clerestory windows above provide additional natural light in this bright, transparent space during daytime hours. A suspended boomerang-shaped fluorescent fixture provides efficient illumination to the master bath area at night and a dramatic look from the outside.

The prominent feature in the master bath is a centrally located free-standing vanity wall, an island which has a pair of sinks on one side and the hidden toilet and shower niches on the other. The terrazzo-style bathroom counter was custom made of recycled glass using the same process as the kitchen island.

The central island in the kitchen was created in Austin using recycled glass in a terrazzo substrate formed from a life-size pattern furnished by designer Lind. The organic shape is mirrored in the light cove above.

Existing kitchen appliances and cabinetry were gutted and replaced with new formaldehyde-free cabinets— stained walnut at the upper cabinets, and clear-coated exposed medium density fiberboard base cabinets.

CaesarStone Quartz Surfaces and Countertops on the kitchen surfaces approximate the look of concrete, while handmade elliptical Heath tiles form a distinctive backsplash. Comprised of 93 percent natural quartz, CaesarStone Quartz Surfaces and Countertops offer the combination of form and function, allowing for a diverse, durable, and practical countertop surfacing material.

All appliances are energy-efficient and Energy Star-rated. In addition, two on-demand Rinnai gas tankless water heaters were installed – one for the master bath and the other for the rest of the house.  Venable said these on-demand water heaters run at about 199,000 BTUs and each have the capacity to provide hot water for up to seven fixtures at the same time.

Green features
In addition to the original concrete, another important green feature of the home is a 5000-watt solar system on the roof that produces about 40 percent of the electrical needs of the house.

Also, Venable said that they replaced all windows and doors with high grade, commercial-look energy-efficient doors and windows, fluorescent lighting throughout, zero VOC wall paint, and Marmoleum flooring in the utility room.

The house was not air conditioned originally and the owners wanted to add central air conditioning and heating, which required Penhall to cut holes in the roof for the two HVAC units. “But we wanted to leave the supporting steel rebar in place,” Venable said explaining that the Penhall x-rays allowed for precision cutting. Then the exposed steel was epoxy-coated before the units were set on top of the new roof openings. Then they built plenoms for duct work by removing the ceilings in the master bedroom closet and in the utility room and brought in the exposed ductwork.

“Before we got the roof finished we had a couple of severe weather changes. It went from warm to cold to hot, and it actually rained inside the house a couple of times through the unfinished HVAC roof openings.

“We learned first-hand that concrete doesn’t dissipate heat or cold by its very nature, so when the weather changed outside, the temperature didn’t change inside the house. Once it’s cooled off, it stays very nice inside.”

The result is an entirely new two-unit HVAC system that was sized according to calculations that took into account the home’s concrete materials, orientation and overhangs. Because the structure is concrete, the HVAC will probably run infrequently in Austin’s generally mild climate; however, Venable said the HVAC is about 80 percent of the rating process.
A Five-Star remodel
There were no problems with inspections and city codes, but the biggest challenge was getting the house the Five-Star rating because few people understand how concrete exterior walls work as excellent insulating factors.

“We got the Five-Star rating, which makes this house unusual – there are not many Five-Star rated houses in Austin right now,” Venable said. “They’re still trying to work out the ratings as they apply to remodeling so sometimes it can get really demanding for the contractor.

“Along the way to its Five-Star rating, however, the homeowner never compromised design for efficiency. Whoever buys this house will have an example of how an energy efficient, green home can also exhibit a high degree of design and detailing–as well as healthy interiors and energy efficiency.”