We recently completed our net-zero farmhouse project. The house has a contemporary design and feel, but the exterior pays tribute to the classic farmhouse designs found throughout the Shenandoah Valley.

Some highlights of the project:

- 0.46 ACH50 final blower door test
- Exterior mineral wool insulation (Roxul Rockboard 80)
- Fiber cement siding (HardiePlank) and double-locked standing seam roof
- 5.6 kW PV system, with islandable capability
- Hearthstone Craftsbury woodstove with outside air intake
- Fujitsu slim duct high efficiency heat pumps
- Renewaire EV90P Energy Recovery Ventilator

This project combined energy efficiency with resilient design. Genesis Home and Energy installed an islandable PV system (discussed in a previous blog). Key electrical circuits will be maintained during a power outage: lighting, wall outlets, well pump, refrigerator and freezer, microwave, etc.

Although we were somewhat hesitant to install a woodstove in a tight house, the client wanted the ability to heat with locally harvested wood (ambiance, resiliency, radiant heat for comfort). No woodstove is airtight, so there were some risks:

- Backdrafting
- Depressurization of the house
- Lower indoor air quality

We mitigated these risks by making the house all-electric, and eliminating exhaust appliances. The range hood is recirculating. The dryer is a condensing, ventless model. We were also careful about specifying a woodstove with an outside air kit--and positioning the inlet and chimney to provide excellent draft.

John Semmelhack of Think Little fame completed several tests to determine if the woodstove would negatively affect the house. He found that the woodstove had a negligible effect on the house pressure (within the noise of precision). This measurement held when the woodstove was cold AND when it was operating.  He determined that the stove pulled between 10 - 15 CFM (cubic feet / minute) when operating. With the outside air intake the majority of that air is supplied from the exterior.

On a crisp winter morning, driving through the neighborhood, it is easy to spot thermal bridges. No, you don't need a infrared camera, or any other sophisticated equipment. Mother nature provides the visual tool. We call it condensation, or frost.

With this simple tool it is easy to see where the insulators did a poor job, or where an electrician installed a recessed can light. And you certainly don't need a stud finder to see the location of the studs and rafters.

Simply put, heat is lazy. It follows the easy path. And it always moves in the same direction---from hot to cold, or more accurately, from a higher state of energy to a lower state. Heat has three modes of travel: they are radiation, convection, and conduction.

RADIATION
No, we're not talking about nuclear energy. Think of fire or sunlight. Even though the air temperature near a fire might be cold, you will still feel very warm when you sit directly in front of that fire. This phenomenon is known as radiant heat flow. In buildings, we don't really worry about this to much, but we do consider it when we think about windows and roofs (i.e. unshaded west facing window).

CONVECTION
Think air. Think movement. Think of a leaky window on a cold and windy day. Can you hear it whistling? A lot of heat will move out of your house in this way, hitchhiking a ride on the air that is flowing outside. For most houses, this is one of the dominant forms of heat transfer (loss or gain, depending on the season). Convective heat transfer is why air barriers are so important.

CONDUCTION
This one is fairly easy to understand. It occurs when heat flows through a material. Metals are great conductors, so heat flows through them very easily. That's why we use them for cooking, right? In houses, conduction is another important form of heat transfer.

When we talk about houses and conduction, we start looking for something called a thermal bridge. Remember, heat is lazy. It follows the easy way out. A thermal bridge is that easy path. It is a solid and direct connection between the interior and exterior of the building.

In Virginia, most houses are built with 2x4 stud walls.* These studs span from the inside, where they are attached to drywall, to the outside, where they are attached to the sheathing. And although we don't think of wood as a great conductor, on hot or cold days, these 2x4 studs become an interstate highway for heat flow.

There are a couple of ways to get around this problem. One, builders can install a layer of rigid board insulation on the outside of the structure. Common materials include EPS and polyisocyanurate foam insulation. Mineral wool is gaining a following though, due to its resistance to attack by insects, as well as its permeability to moisture. This is becoming more and more common with progressive builders. In fact, it is a requirement of the 2012 IRC code for Climate Zones 6 -8.

Or two, a builder can create a double-stud wall (one is structural, the other is non-structural). The studs in this kind of wall do not span from the inside to the outside; there is a gap between them that is later filled with insulation.

Either method creates a thermal break---instead of a thermal bridge---and makes it that much harder for heat to flow. As a homeowner, you get greater comfort and lower energy bills.

*For the historically minded, this type of construction dates back to the late
1800's, and is partially a result of the Great Chicago Fire of 1871. Rebuilding
efforts stimulated the search for quick and cost effective framing systems. 2x4
lumber met the minimum structural requirements for two-story residences. Throw in some machine drawn nails, and you have the birth of modern-day framing systems. We have since transitioned from balloon framing to platform framing, but stud sizes have remained fairly consistent for > 125 years.

The pace of change in electronic devices is astounding.

As an example, in a little over a hundred years, we went from the telegraph---the standard method for long distance communication---to the cellular phone.

And that pace of change is only accelerating.

In 1992, Motorola came out with the Bag Phone, a premier product that gave users nearly three hours of talk time. It weighed ten pounds and served a single purpose. Fast forward to 2012. Today we have the iPhone 5. It weights a mere 3.95 ounces and can perform a dizzying array of functions for up to eight hours.

If only we could upgrade our houses like we upgrade our cell phones . . .

Most people have the financial ability to upgrade their phone every year or two, and in some cases they have to upgrade (planned obsolescence). But houses? Not so much. Who can afford a $100,000 gut rehab? It costs too much and takes too long. It just doesn't happen very often.

If you look at housing over the last century, there has been a sea change in technology there too. Yet, in many ways, we're still building houses the same way we did in 1912. We've moved from coal furnaces in the basement to high efficiency natural gas models . . . but chances are the furnace is still sitting in the basement of your new house.

Albert, Righter, & Tittmann Architects designed a passive house project for the Charlotte, VT Habitat for Humanity. They also produced a great graphic that shows the evolution of housing. It clearly illustrates what was, what is, and what could be . . .

Forgive me, but that almost sounds like Dicken's warning to Ebenezer Scrooge, in A Christmas Carol. I think that incessant holiday music is takiing effect!

These days, you won't find anybody carrying around a Motorola Bag Phone, but most people are still living in 19th and 20th century houses---and in many cases, we're still building them as if nothing has changed.

If you study the drawing of the 21st century house, you will see that it is the energy efficient house. The technologically advanced house. Yet in many ways, it is the simple house.

It's airtight and ventilated with heat recovery. It has more insulation, fewer bells and whistles. It accepts the sun in the winter and rejects it in the summer. It uses small devices for heating and cooling, devices that cost little to purchase and even less to operate.

Upgrading a house to meet today's energy efficiency standards is costly and difficult. For most, it only makes sense when the structure is sound, but all of the exterior finishes are failing.

But if you are building a new house, why go back to the 20th century?
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Happy Holidays to you and yours!