David Horobin, principal of Estudio Verde Architects in
Napa, Calif., designed a fire-resistant, sustainable home for his family in
2008 with the help of contractor Patrick Bentley of Bentley Construction and
Concrete. The design and construction of the home took into account the effect
on the neighbors, placement, profile and mass of the structure, building
materials, utilities, and aesthetics.
Energy and Resource
Beginning with site placement, careful attention was given
to energy and resource efficiency. The home’s footprint is shaped like the
letter “L” and angled to accommodate the original land contours. This minimized
the need for grading and rock excavation. The site placement also plays the
role of good neighbor by mitigating obstruction of the upper neighbors’ view of
the San Francisco Bay.
The 2,700-square foot home is oriented specifically to maximize
views, reduce solar gain, and ensure privacy. The kitchen windows primarily
face south and have extended overhangs to accommodate winter solar gain at a
lower sun angle while shading the same windows from a higher angle of sun in
the summer. Most of the bedroom windows face east to accommodate morning solar
gain and ambience, using low-E glass. There are minimal windows on the west
side to limit the evening solar gain in the summer, which can be very strong
The entire envelope of the home was designed to deliberately
avoid the use of mechanical cooling equipment. The north wing has concrete
floors incorporating plenty of thermal mass for the radiant system. The use of a
controlled ventilation (CVC) system in the basement area of the east wing
connects the thermal mass of the earth to the interior of the house, thereby
taking advantage of the earth's constant 55-60 degree temperature to both heat
the house partially in the winter and help cool it in the summer.
Except for the upstairs cross walls, all exterior walls of
the house are built with insulated concrete forms (ICFs). The form chosen
consists of a six-inch concrete core with just over two inches of expanded
polystyrene (EPS) on each side. The equivalent R-Value created by the thermal
mass of concrete encapsulated in two layers of R-12 EPS amounts to
approximately R-65. Compared to conventional framing where R-19 fiberglass
insulation may be reduced to an average of 13.5 because of the inconsistencies
of wood framing, the ICFs provide excellent energy efficiency.
ICFs limit the potential infiltration or exfiltration from
electrical boxes and plumbing punctures in the envelope, which decrease the
efficiency of conventional walls. The walls of the garage are constructed with ConForm
ICFs, a product designed by the Horobin and manufactured in Utah. The garage is
unheated but always remains at a constant temperature because of the Conform technology.
Except for the garage roof, the home’s roofing is
constructed with a structural insulted panel system (SIPS). With an R-Value of 45 compared to a
conventional framed system, which may only achieve an R-22, the decision was
easy. With the added benefit of being able to assemble entire hip roofs (three
of them on the east wing) and the gable roofs on the garage floor, SIPS cut
short-term construction costs as well as long-term energy consumption.
The combined energy
elements of the design and construction, including the choice of hot water
radiant heating, provide a maximum heating load of 40,000 BTUs. This amounts to
approximately 25 percent of a similar design using conventional materials such
as wood studs. A 50-gallon water heater provides all the heating and domestic
hot water used in the home and at a greater comfort level than conventional
heating systems. The master bathroom is heated with an in-floor electric
radiant system. This was installed prior to applying the tile floor finish and
is controlled by a timed thermostat, which provides a toasty ambience for bare
There are two operable and remote-controlled skylights in
the entire house. They are specifically placed to provide thermal venting for
the highest ceiling elevations of both the one-story wing (in the kitchen) and
in the master bathroom for the two-story wing. The bathroom skylight is located
directly above the main shower and tub to allow for moisture venting as well as
heat, which stratifies at the higher points. The kitchen operable skylight is
specifically placed above the double ovens and the stovetop to vent unwanted
The choice of hot water radiant heating was an automatic for
the Horobin residence. In the concrete floors of the north wing, which includes
the kitchen, office, dining room and entrance lobby, Pex piping is placed in
the floors. These zones all have two inches of EPS foam faced with reflective
foil placed between the concrete and the compacted gravel base, providing an
R-8 insulation value to essentially reflect the energy up through the slab into
the rooms above. The ICF walls provide perimeter insulation of R-65 for all
concrete slab areas.
The living room has two runs of piping that are placed under
the subfloor and reflected upwards into the room. The master bathroom and
shower has an electric radiant cable system placed in the mortar bed below the
tile controlled from the master bedroom. All controls, pumps, thermostats and
manifolds were tested by the manufacturer to ensure the entire system balanced.
The Horobins lost a house to the Lexington Hills fire above
Los Gatos in 1985. Since then, David has encouraged clients to follow his
example and build responsible, safe homes that mitigate fire damage. The use of
ICFs provides an entire concrete structure with a minimum of four-hour
protection in the walls.
The entire roof and overhangs are covered with GoldBond, a
thin fire-protective fiberglass and gypsum sheathing. The use of clay tile and
careful placement of bird-stops to prevent thermal fire-chimneys under the
tiles adds to the fire resistance of the entire structure.
The use of SIPs completely eliminated the need for ceiling
or roof vents, a huge concern for fire crews and homeowners of conventionally
constructed homes. Fires usually travel uphill and the downhill walls of the
home are constructed with no windows on the first floor. With most of the
windows on the east side—windows being the weakest link in fire consideration
of any structure—there is little danger from fire as the trees and vegetation
are limited to the other side of the property lines, far away from the house.
From an interior standpoint, the entire structure is has
sprinklers per the City of Napa code requirements. All floors are tile or
hardwood as well as all interior window and door detailing – this eliminates the
use of wood trim, providing simple and elegant aesthetics as well as minimizing
potential of fire. Ninety percent of all interior walls are pre-manufactured
steel frame panels from Codding Industries, few of which are load-bearing
walls, thereby mitigating the potential of structural damage in the event of a
All three exterior decks are finished with a fire-resistant
composite decking material.
The original structural design offered the alternative of
using Helix Fiber, a helical galvanized steel fiber designed at the University
of Michigan to enhance the reinforcement of concrete in seismic conditions.
Openings, corners and foundations still require conventionally designed steel
reinforcement but the fibers get mixed in the concrete at the batch-plant. The
advantage is that they make every cubic inch of the concrete into tensile concrete,
as well as eliminating many hours of steel reinforcing fabrication and material
on site. Otherwise, the six-inch concrete walls provide compliance with all
structural and seismic codes as required by the Uniform Building Code.
Fortified for Safer Living
a result of the structural and fire aspects of this home, the owners were
awarded the first west coast "Fortified for Safer Living" certificate
by The Institute for Business & Home Safety (IBHS). IBSH promotes safe
building construction in any natural disaster-prone zone in US.
The designer specified
a concrete mix of 40 percent fly ash. Adding fly ash increases the strength
of concrete and is less porous than a conventional mix.
benefits of using fly ash include:
- Delays the heat of hydration
and reduces thermal cracking
- Improves the workability of
- Makes the mix homogeneous and
reduces segregation and bleeding
- Finish (for slabs) is
improved due to perfectly spherical fly ash particles
- Permeability is substantially
reduced which enhances the life of the structure
- Contributes to the long-term
strength in concrete
- Fly-ash is a byproduct of
combustion chamber and otherwise destined for a landfill
Bedroom number three has recycled wine-cork floor tiles and
a notice-board wall. The material returns the corks to their place of origin in
Napa and provides a unique and beautiful finish. It provides additional
acoustic and thermal insulation as benefits.
The home’s interior walls are constructed with steel beams
by Codding Industries instead of wood. Panelized from 18-gauge steel
C-channels, the contractor was able to lift each panel into place from the
stack delivered to site. All first-floor interior walls were placed and
attached within a 48-hour period. Steel
walls are generally very reliable in tolerance compared to wood studs, which
delights drywallers who have a much easier time as they can rely on the
straightness of the walls.
The house is extraordinarily quiet. Unless the kitchen
windows are open, all street noise is eliminated. This is a deliberate design
element caused by a combination of the placement of the garage, the use of ICFs
and SIPSm and few west-facing windows. The owners used leftover SIPS
polystyrene foam between the bedrooms to mitigate sound transfer.
To support the driveway and path to the main entrance,
native large boulders from the property were dry-stacked to create a natural
and rustic retaining wall.
The main driveway and parking area are made with “ginger
rock,” a beautiful and locally mined fine rock material. As a pervious
pavement, the need for perimeter and foundation drains was eliminated.