Article No: 129

2006-05-02 13:22:52
Reno ICF stands up to wildfire
By: Carole McMichael

Photography courtesy of Rentsch Construction

Having a "hot time in Reno" took on a new meaning earlier this year for Cindy and Bill Rentsch and several of their neighbors. In a hilly area south of Reno where, for the last year, the Rentsches have been living in their ICF-built home, a brush fire started. Within a couple hours, whipped by high winds with gusts of 30 to 40 miles an hour, the whole area was in flames.

"My mother got through to the house just before the firefighters closed the road," said Daniel Rentsch, son and architectural designer of the home. "The flames got within 20 feet of the house, and the heat of the fire was so intense it broke one window. But because the house is so tight from ICFs, it didn't suffer even smoke damage."

Others in the area were not so lucky — 15 neighboring houses were lost. Some houses burned to the ground leaving only chimneys standing and slabs to mark the sites of what were once stick-built homes.

ICFs in Reno
It would seem that Daniel and Bill Rentsch, owner of Rentsch Construction, collaborated on their first ICF home project — the first in the Reno area — at just the right time. Bill, normally a contractor of wood-frame residential construction, wanted to try something new.

"Building with ICFs is starting to catch on in Reno," Daniel said, "because it is cold here, and ICFs provide good insulation. Originally we looked at straw-built systems, but found ICFs get thermal and sound-reduction properties similar to straw-built, but you do not have to deal with the moisture problems straw-built has. Also, the walls provide good load-bearing. In straw-built, load-bearing is more restricting because it uses post and beam. With the concrete, the house is really nice-looking because you don't need as much length of the wall to get the same amount of shear that you would get in a much larger wood structure.

"The cost of using ICFs wasn't a lot more than it would have been if we built from wood. Because we have a lot of large windows openings in the design, we needed a lot of structure to get the size openings we wanted. To get that with wood, and still meet the seismic standard for this seismic zone, it would cost nearly the same."

The lucky house
The Rentsch's 10-acre lot is pretty steep, so the 5,500-square-foot house has a daylight basement facing pasture land below with the street-side entrance on the second level. There are four bedrooms and four baths, an office, a great room with the kitchen attached and a dining room and living room combo. Downstairs, there are two bedrooms and a media room. The style of house is contemporary with a stucco and stone exterior. Upstairs, the ceilings range from 9 1/2 feet to 11 1/2 feet. The living room and great room have vaulted ceilings with exposed beams. There is a 1,200-square-foot shop where Bill works on his car collection, tearing them down and rebuilding them from scratch. There is also a 1,200-square-foot detached three-car garage.

"The basement is slab on grade," Rentsch said. "The floor above is wood-framed with open-web joists, then 2 inches of lightweight concrete for the radiant floor heating. We did that throughout the house, using a hydronic system that is the only heating system in the house. My parents have been really impressed with it so far.

"The main problem, however, is to keep out the sun. We get plenty of daylight facing south and west, and get sunlight in every room. On the west, we have trellises on the dining room windows, which are planted with the type of vines that are in full bloom in summer but die back in winter. Although it gets in the high 90s and 100s, the house never gets above 72 degrees inside (without air conditioning). There is a lot of heat loss through the huge windows. We just open the windows up at night and close them in the morning. It stays cool all day. It's amazing."

ICF choice
Ed Zweigle, a commercial and residential contractor since 1961, started working with ICFs seven years ago. About five years ago, after dealing with other ICF products, he chose Nudura forms manufactured by Nudura Corp. based in Barrie, Ontario.

"There are a lot of reasons I changed," said Zweigle, now a distributor for Nudura, "They are much easier to use and bigger, so there is less labor involved in assembling them. They are 8 feet long instead of 4 and 18 inches high. They fold flat for transit — you are not shipping half air — and are unfolded onsite. One Nudura form covers the same area as 13 1/2 concrete blocks. The corner forms are reversible, whether left or right, and the corners even fold. The straight forms go either way too, so there is no waste. You can cut the block every 2 inches. Also, the blocks snap together so you don't have any floating or settling. To my way of thinking, it is just a much better product. The people who designed the Nudura block had their ducks in a row.

"The Styrofoam is 2 5/8 inches on each side. With Nudura, you can have cores from 4 inches up to 12 inches. On the Rentsches' home, they used an 8-inch core for the retaining wall for the walkout basement and 6-inch core for the rest of the house. The finished width of the retaining wall was 13 1/4 inches thick and the rest were 11 1/4 inches. For windows and doors, builders can use Easy Buck forms or a wood buck." (They also have end caps that provide insulated bulkheads and height adjusters.)

Nudura onsite
The footing for the Rentsches' retaining wall was about 5 feet and for the rest, about 3 feet. Rebar came up out of the footing, tying it to the walls. Because there are rebar chairs molded into the forms, the rebar just snaps in. The whole building process is faster because rebar is only tied vertically, cutting down on labor. The placement of rebar is determined by the structural engineers. Webs are 8 inches on center, so rebar is usually 18 inches on center horizontally and 16 inches on center vertically. Sometimes it is 24 inches on center vertically, depending on the load from window and door spaces and corners. For window headers and door lintels, builders usually double up on rebar going 2 feet past the opening.

On the Rentsch house, the forms were stacked on the footing and then the footing and one course was poured. Next, the slab was put on top of the footing and butted up against the foam forms, and the radiant heating was installed.

"In general," Zweigle said, "we can pour 10 or 12 feet with no trouble. We use an external vibrator (a Nudura product) that consolidates the concrete. It attaches to the bracing with a vice grip and vibrates the whole wall with air. You can use a little air or a lot. These forms don't have a blowout unless someone cuts the webbing. Some ICFs have blowouts because they are not manufactured to fit as accurately as Nudura's. These things are right on the button. Once poured, the concrete cures in a couple days. Concrete cures inside the form and ends up being twice as strong as it would if the foam was removed."

Easier than you think
According to Zweigle, the Rentsches' house was pretty straightforward, so preplanning went smoothly. The engineer had no problem with stamping the plans using ICFs, especially since the forms created solid, reinforced concrete walls.

"In my area and a lot of the West," Zweigle said, "ICFs are becoming more common. And at trade shows, there are usually building department people who come over and have a look. On a job, I meet with the code people if there is a problem and give them the technical info. We also offer some training sessions. When inspectors understand that the foam isn't holding up the wall, and the homeowners explain that their heating bill will be cut in half, they start to listen."

For first timers, getting the crew to learn the ICF system may be a problem. Most distributors and manufacturers will offer training for the contractor and crew.

"Because my Dad was a contractor," Rentsch said, "he could play it by ear." Zweigle came to give him a three-day warm-up with the product to get familiar with how to set it all up and brace properly. He also helped set up the first three or four courses up to the first pour.

"I have worked with homeowners who wanted to be their own builder," Zweigle said. "I am a distributor and don't supply a crew, but if the homeowner/builder can walk and chew gum at the same time, he can do this. We explain that if he doesn't get the foundation right, the roof will give him trouble. So we spend time to make sure it is level and square. Before the pour, it is checked to make sure everything is plumb and properly braced. I won't sell the system to someone and just let him try to figure it out. I've got my name on this and don't want the house coming out bad."

The Rentsches did not have any problem with introducing the electrical or plumbing subcontractors to ICFs. "After we talked to the electrician," Rentsch said, "he was really excited that he could just take a hot knife, cut a groove and put the wiring in. As for the plumber, he was the one who did the radiant heating. We did coordinate plumbing that would go outside before the pour, but there were no plumbing fixtures in exterior walls."

What's ahead
"We got a lot of good responses to my parents' house," Rentsch said. "We have a client who wants the exact same house with a slight modification. Everyone admires it — how well-insulated and quiet it is. My dad also plans to start a 2,500-square-foot lake house out of ICFs with a more contemporary style. ICFs are definitely taking off. I think it is going to ramp up in the next couple years."

Zweigle also finds that business for ICFs is good. He just got a job for a 300,000-square-foot office and warehouse. On the residential side, he is currently working on a subdivision with 15 ICF houses. He gets new business though word of mouth, trade shows and from his Web site (