Building energy

Demo efficiency home under construction
Florian Dengel, owner/builder of ALP Development LLC, shows the air-tight windows used in the construction process of this energy-efficient home near Linden. Rich Cooley/Daily
Florian Dengel, owner/builder of ALP Development LLC, stands inside this sustainable home he's constructing near Linden in Fauquier County. Rich Cooley/Daily
Engineer Ottmar Dengel sits beside a wall sample for this home being built by ALP Development LLC off John Marshall Highway just east of Linden in Fauquier County. The German-engineered home will feature air-tight insulation that yields a typical heating or cooling bill of $20 to $30 a month. Rich Cooley/Daily

LINDEN — German engineering in home energy efficiency is coming to the U.S. in the form of a house off of John Marshall Highway near Linden.

Front Royal-based ALP Development partnered with German construction company Kaufmann to bring the K-Plus construction model to America. Father and son team Ottmar and Florian Dengel chose Linden for the central and convenient location close to Ottmar Dengel in Front Royal.

A K-Plus house requires 10 percent of the energy a standard house uses. With installation of new Tesla Powerwalls, company owner and builder Florian Dengel said the house could be completely self-sufficient.

While the passive house standard for insulation R-value is R-50 to R-60, the K-Plus walls fall slightly short with an R-level of 40. At the same time, the 15-inch K-Plus demo house walls are about half as thick as typical passive house walls.

Compared to the standard insulation R-value of about R-12, engineer Ottmar Dengel said this middle ground of thickness and insulation is enough, costing the owner around $22 per month.

“We have something unique — this is the wall, and that insulates you acoustically,” he said. “It’s very stable and the special feature is … it doesn’t burn.”

Walk-through demonstrations include showing a scorched section of the inside wall, which doesn’t catch fire because the boards are so airtight. In addition, samplers can take a sledgehammer to the dense inside wall to learn how stable it is. Florian Dengel said the team held a successful open house and he’s shown the house in its unfinished state to other builders with interest.

“It’s really nice to show it in this condition,” he said. “Usually no one wants to see a house like this, but this house is so different.”

ALP Development bought three wooded lots in December 2012 and installed wells and sewer systems for future homes.

Filled with pre-cut panels and full walls, the first shipping container from Europe arrived at the site in May, and Florian Dengel said his team had the structure built up to the roof in three days. With all the kinks worked out, he said future projects will take even less time.

Although he keeps the work team to a crew of two to three devoted carpenters, Dengel said the K-Plus model project will only take about 10 to 12 weeks of work, whereas other projects he works on can take more than twice as long.

The team still requires one more partial container from Europe to complete the house, finishing the vital setup of the geothermal and air handler systems. Once the final container arrives sometime around late August, the team will tweak the air handler and finish the roof, siding and interior drywall. Dengel estimates the major construction – without any major hang-ups — will be finished by early October, and the house will be fully fitted and furnished within another year.

According to Florian Dengel, the specialty Swiss tape for the OSB panels has only become available within the past year, and other key materials are still not for sale within the U.S. yet. Some may not become available for a number of years.

“We are trying to buy as much here as we can, but it’s not so simple,” Ottmar Dengel said.

Florian Dengel said building inspectors have come out to the demo house sometimes on back-to-back days to check on different stages of development for a kind of project they haven’t seen before.

“Getting the permits in for the plans took a little while, but they saw what it was; they’ve taken care of us,” he said.

Eventually ALP Development will look to sell the model house and begin working with clients on K-Plus versions of any architectural plan. Further down the road, Florian Dengel said they will look into benefits and subsidies the homeowner may qualify for.

The K-Plus model is particularly applicable for vacation homes and in locations with few or no electric hookups. Florian Dengel said he hopes to use this house as a demonstration for those in the market for second homes or a smaller niche market in northern Virginia for primary homes.

Contact staff writer Rachel Mahoney at 540-465-5137 ext. 164, or

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