Passive House

Outrageous energy-efficiency …sublime comfort.
Reduce energy consumption by 90% and enjoy amazing comfort with a Passive House. Interior temperatures are always even and constant …yes, including in front of windows… and the air is always fresh and clean.

One Sky Homes has fully embraced The Passive House concept and incorporates the Passive House standard in it’s high-performance homes including Zero Energy Home designs. One of only a handful of building design/construction professionals in the Bay Area rigorously trained in PH methods and implementation practices, OSH is a Certified Passive House Consultant (final certification pending) under the authority of the Passive House Institute US.

The designation ‘Passive House’ is a building standard and construction concept that acheives the highest standard in energy-efficient construction available in the world today. Originating in North America in the late 1970’s as the “Super-Insulated House” , the concept was further developed in Northern Europe in response to rigorous energy standards for new buildings mandated by the Swedish government in 1988. In 1990, the first prototype was designed and built by  Professors Bo Adamson and Wolfgang Feist in Darmstadt, Germany. Today, there are an estimated fifteen thousand Passive Houses in Europe, mostly in Germany and Austria.

Heat your home with a hair dryer

The Passive House standard is a design methodology that focuses on super-insulated, airtight construction, maximizing useful solar heat gains while minimizing unwanted gains during summer, using continuous fresh air ventilation with heat recovery to reuse internally generated heat, and installing high performance windows and doors to minimize heat losses and maximize occupant comfort.

For space heating and cooling, a Passive House typically uses up to 90% less energy than a conventionally constructed home meaning that it can often be heated with the energy equivalent of a hair dryer. There is typically a significant reduction in the size and cost of the heating system.

These exceptional energy savings are achieved by following seven specialized design and construction principles:

Super-insulate

To block or slow heat transmission and maintain a relatively constant temperature inside a building, it must be incased in a heavily-insulated shell or envelope. The envelope of a Passive House includes the wall, roof and floor assemblies insulated to a level appropriate for the particular climate where the house is located and which achieves specific energy consumption standards.

Eliminate Thermal Bridges

Heat quickly finds its way out of a building in a path of least resistance leading to serious heat loss. The path is easily created from an area of higher thermal conductivity such as edges, corners, connections and penetrations. The goal of Passive House construction is to block thermal bridges by isolating them (thermal break).


Infared image of a wall protraying cold areas caused by the studs acting as a thermal bridge (dark lines).

Make It Airtight

The goal of an airtight environment is to minimize heat losses. Drafts, either hot or cold, make a major contribution to wasted space conditioning.  Also, penetration of the building by warm moist air can cause structural damage by condensation inside the wall. The Passive House standard achieves airtight construction by wrapping an intact, conitinuous layer of materials around the entire building envelope.

Specify heat recovery ventilation.

Traditional HVAC systems are dramatically simplified, down-sized and in some cases eliminated in a Passive House. Instead, Interior Air Quality (IAQ) is maintained by a smaller ventilation system, referred to as a fresh-air furnace. This heat/cold recovery ventilator retains energy that has already been generated in the house instead of venting it to the outside. Measured amounts of fresh air circulate inside the house while at the same time exhausting stale air from the house. A Passive House in a warm climate is ventilated with high efficient energy recovery ventilators (ERVs) or in cold climates, heat recovery ventilators (HRVs).

Specify high-performance windows and doors.

Windows and doors significantly affect heat loss in standard construction. In the Passive home, insulating value determines which windows and doors will be used in construction. Major developments in building construction include the development of fully operational, high performance, triple-glazed windows. The gaps between window panes are filled with inert gases like Argon or Krypton which provide better insulating values than air.

Optimize passive-solar and internal heat gains.

Many issues confront the Passive House designer when considering the orientation of a new structure and how it will affect its energy gains and losses. As sunlight falls on or in a house it is converted to heat so the first consideration for a designer are areas in a house that will be used most frequently by the occupants such as living rooms, dens/offices and bedrooms. These areas should be located on the south-facing side of the structure, while garages, laundry rooms and storage areas should be situated on the house’s north side.

Passive solar heat is generated through windows that must be oriented for optimal solar gain. Roof eves and proper shading can assist in preventing excess solar heat gain while still allowing heat gain from low winter-time sun angles. View lots and landforms can challenge even the most creative designers if they are not located in the optimal place for a passive house design.

Model energy gains and losses using the Passive House Planning Package.

Sophisticated simulations were once required to calculate energy balance in buildings but now The Passive House Performance Package (PHPP), a spreadsheet structured design tool, assists designers and architects to reliably calculate heating energy balances, heat distribution and supply and energy demand using managable data input. With reliable accuracy, the PHPP software program is able to describe the thermal building characteristics of an unconstructed passive house design.

Air Tight Envelope: Options for sealing

We’re shooting for the Passive House Standard on this project, which means one of the big targets is that it’s got to be really air-tight. Below 0.6 ach50, to be precise. Since this is the first time we’re attempting this, we’re testing a few different strategies. One of the materials we’re using is closed-cell spray foam. Here we’re spraying it between the floor beams and the crawl space to completely fill the gap between the rim joist and our nicely insulated stem walls. The idea is that the spray foam insulation will create both an effective continuous thermal barrier and will also seal any gaps we have in our building envelope. Keeping our crawl space well sealed from the outside will also ensure that no contaminated air, earth gases or mold spores will infiltrate into the living space.

Roof Insulation: Radiant Barrier

The roof absorbs radiation from the sun and is heated. This heat then passes into the underneath side of the sheathing through conduction. The hot roof then radiates thermal energy into your open attic. Eventually, heat will make its way from your attic into your home through a combination of radiation, conduction and convection. 93% of this heat will come through radiation.

Ridge Ventilation

More than any other part of your house, the roof is subject to extremely high heat, both on and under the roof deck. In the summer, on a clear 90°F day, the sun can heat the roof shingles to 170°F. Without adequate attic ventilation, heat can routinely build up to as high as 140°F inside the attic.

Craning Roof Materials

What to do with tons of roofing materials that are needed on the roof?

Roof Framing: Raised Heel Trusses

Second Floor Framing: Moving Thirteen Tons of Framing Materials to the Second Floor

Of all the challenges builders have today, one of them is NOT heavy lifting.

The mission: To move thirteen tons of materials from here…

…to here.

Advanced Framing: Less Wood, More Insulation

Advanced Framing, sometimes called Optimum Value Engineering (OVE), refers to framing techniques designed to reduce the amount of lumber used and the waste generated in the construction of a wood-framed house while maximizing the energy efficiency of the wall assemblies by making more room for high R-value insulation of R3 to R6 per inch instead of wood at only about R1 per inch.

The US Department of Energy has been responsible for the research that defines and supports Advanced Framing Techniques. The following chart was created by the DOE:

The most basic feature of Advanced Framing for a two-story home is changing the wall frame from 2x4s @ 16″ on center to 2x6s @ 24″ on center. Even though we use lumber that is 50% larger we actually are using slightly less lumber since we are using wider spacing and lots of techniques like two-stud corners which use fewer studs than normal. Here we have just tilted up the first 2×6 @ 24″ on center wall section.

Optimizing the use of lumber can save significant cost. For example, the Uniform Building Code even allows 2 feet on center 2×4 stud spacing in one-story dwellings and on the top floor of multistory dwellings instead of the conventional 16 inches on center. Also, using two-stud corners can save as many as 40 to 50 studs in a house.

Advanced framing methods may reduce wood use up to 20% and improve wall thermal resistance values from 5 to 10%. Just the corner and wall intersections of typical homes can add up to 10 or more feet of wall that is not insulated.

This doesn’t include the additional insulation value you get by filling a 2″ deeper wall cavity with insulation. A standard 2×4 wall cavity would achieve R-13 when filled while a 2×6 wall cavity can achieve R-20 with the same fill materials. This is over a 50% increase in R-value, and insulation is pretty cheap.

The small window rough openings high on the long wall are sized to fit standard 24″ o.c. stud bays so there are no extra studs used to frame the openings. This is another feature of Advanced Framing if you have managed to get the building designers on board from the start. Most of the windows in this home have been designed to fit a single or double wide stud opening …no extra studs.

However, we are in earthquake country on this project so the structural engineers require additional studs for “hold down” connections to the foundation and horizontal blocking for metal straps above and below window and door openings. Even so, we still have more room for insulation and the wall cavity is deeper so it will accept more insulation. Enough to cover the horizontal blocking in this wall section and thereby reducing thermal bridging.

Here we have one example of an insulated header with some EPS foam on the exterior side of the header visible in this photo of an 8ft wide window opening. Below is another type of insulated header with EPS sandwiched in between LVL headers.

The house is just as strong as a conventionally built house. We save trees and money and we achieve a higher insulation content which yields increased comfort and energy savings. Additional construction cost savings result from reduced waste disposal, which also helps the environment. A win-win-win by all measures.

We will post some other stories with more details on the Advance Framing techniques we used on this project.

Advanced Framing: Two Stud Corners

Here’s another classic ‘Advanced Framing’ technique: building corners with only two studs, or sometimes three to keep the structural engineer happy in earthquake and hurrican zones. This technique reduces framing lumber and also allows for more insulation at the building corner (a space that usually goes un-insulated.)

By eliminating all the non-structural lumber from our exterior corners, you can see how there is more room for insulation. A 2×6 stud has an R-value of 6.8, while the insulated cavity can easily have an R-value as high as 21. You can then understand how fewer studs and more insulation will drastically improve the overall performance of our walls.

Here’s an image of a corner with double 2×6’s at one wall end to support a Holdown and a single 2×6 on the other wall end for a total of only three studs even on this structurally important “Shear wall” corner. Other corners have just two studs total, but in both cases there is still room to fill much of the outside corner with insulation. We’ve used some scrap pieces of OSB here on the inside edge, to act as our nailer for when we install our interior gypsum wall board later on.

Ladder Blocking: Framing Technique for Even More Insulation

Ladder framing or ‘ladder panels’ creates space for more insulation while reducing the amount of wood needed to frame the home. By using less wood but keeping the structural integrity of the frame, we are using what engineers call “OVE,” or “optimal value engineering.”

The best application of the ladder framing technique is when we connect an interior wall to an exterior wall. By using short lumber pieces and attaching them between the studs of the exterior wall, we provide a nailing surface to support the interior wall. We can make use of scrap lumber to accomplish this.

With the exterior sheathing in place you can see the space created for insulation behind each of the perpendicular interior wall intersection studs. This eliminates a thermal bridge.

We often use ladder blocking even on interior wall intersections to save lumber.

Ladder blocking used at the intersection of interior and exterior walls provides a nailing base while allowing space for continuous insulation in the exterior wall behind the ladder framing. Another simple way to improve our building envelope by making sure we reduce those thermal breaks.