Building a Net Zero Energy House

Monday November 10th

There are two requirement for houses to be built in Katywil: they must be small and they must be near net zero energy.

“Small” is a relative term and one’s perception of what a small dwelling is depends upon what century they were born in, or what part of the world they live in today.  According to the National Association of Home Builders, the average home size in the United States was 2,700 square feet in 2009. Many of our great grand parents raised their 5 children in houses smaller than 1000 square ft that had only one bathroom. In most of Europe today the average square footage is 850 square ft. And in much of the developing world, an 850 square ft house is unimaginable luxury.

A “Net zero energy home” produces as much energy as it uses. In New England with the harsh winter climate, this is an impressive feat. But, builders here have been building and achieving near net zero energy homes for at least the past decade. Every year there are building competitions and awards for Net Zero Energy Homes. Given that, we are surprised that the net zero energy building movement has not caught on in the mild Mediterranean climate of California where net zero energy is so much easier to achieve.

Achieving net zero energy can be accomplished in different ways. The 8 new homes built in Katywil thus far provide a good example of this. All 8 homes use different heating systems, have different windows, wall thicknesses …. etc. That said, to achieve near net zero in the New England climate Green Builders generally agree on a set of “optimal” building guidelines. No surprise, but size is on the top of the list!

– 1000square feet is the maximum recommended square footage

– Square floor plan, as the aspect ratio tends more rectangular, efficiency decreases

– Flat ceilings, no cathedral ceilings or other such fancy features

– South facing home orientation to maximize passive solar effects

– No more than 8% area to be windows, 5% of these to be on the south side of the house

– Triple pain windows

– Roof overhangs to allow maximum sunlight in winter when the sun is lower as well as a level of sun protection in the summer months when the sun is highest

– No trees on the south side of the house in a proximity where they would shade the house, plant trees on the north side

– 12 inch thick walls (in Katywil dense packed cellulose is the insulation of choice for environmental as well as health reasons, typically wall insulation is R-45 and ceiling is R-62

– Single story dwellings, no basements

– Photovoltaic array on the roof

Charles' house is the first Katywil house.
Charles’ house is the first Katywil house.

If you do all of these things and have a conscientious builder who is meticulous about sealing the envelope you are pretty much guaranteed to have a zero energy house. However there is some wiggle room in here. It is possible to achieve zero or pretty darned close to zero if you do most of these things, but deviate just a bit on a few of them per your personal needs or wants. The homes build in Katywil so far range from 950 square ft to 1800 square ft (violation of rule #1 for almost everyone!). All homes take advantage of the wonderful south facing slopes, have a south facing orientation with two stories, the lower story being a walk-out basement – except Lynn’s house which is on flat land.

Lynn's adorable 950 square ft house - the smallest Katywil house
Lynn’s adorable 950 square ft house – the smallest Katywil house

All homes have double walls (12 inch thick) except one (which has 7 inch thick walls). All homes have triple pane windows, except one (double pane). All houses (except one) have a cathedral ceiling in the living/dining room. So you can see there has been some deviation from the guidelines here and there, everyone has departed from the basic set of rules somewhere. But despite this, all house have successfully achieved near net zero status. They are incredibly “tight”. Even when the temperatures dip into sub zero territory, it feels cozier inside than the typical California house. There are no drafts in these houses at all, and that makes such a huge difference. All houses except one have a wood stove (in addition to their main heating system). However, everyone is quick to point out that the wood stoves are for ambiance on a cold day only! In fact, when the wood stoves are running the house becomes too toasty. So far everyone has gone a different route on their choice of house heating and domestic hot water heating – but that alone is a subject for another posting.

Peter and Kaylee's house is 3 stories but very tight and with a HERS rating of 5(out of 100) it is pretty much net zero
Peter and Kaylee’s house is 3 stories but very tight and with a HERS rating of 5(out of 100) it is pretty much net zero


What has the Hadley family decided to do? In recent years there has been a lot of hype in the US about the “Tiny House” concept. Readers in Sonoma County might be familiar with Sebastopol’s Jay Shafer and his company Tumbleweed Homes which sells tiny house designs from 117 square ft to 750 square ft. Jay made popular the “tiny house on wheels” and is credited to be the originator of the tiny house movement that has spread across the US. The Hadleys have been fascinated with the tiny house concept. Indeed we did visit and tour Jay’s three “Tiny House on Wheels” models in Sebastopol. They are an incredibly creative use of space. That said, they are definitely geared for the single person, and they do not cook! We have spoke with many people who live in these tiny houses. To date none of them are cooking meals every night. Most nights tiny house dwellers grab a bite out somewhere. Cooking in the tiny house kitchen means something on the order of preparing Raman noodles or quick cook oats. Even Jay himself has upgraded his square footage now that he has been joined by wife and child. Still, while we are not up for living in 117 square ft, we have spent much time pondering how we can minimize our square footage and what is the right square footage for us as a family unit. Before leaving California I checked out every book that the Sonoma County library system had on this subject and since February 28th (Agilent departure date) this has been the subject of countless Hadley family conversations.

In July we put ourselves to the tiny house test with the purchase on our 23ft camper trailer – 184 square ft of living space! This was our home for the next 4 months. Learning: 184 square ft is way too small for 2 adults + 1 7-year old + 1 Australian Shepherd pup. Then on October 1 life circumstances landed us in 2600 square ft when we moved into the log cabin that we are currently renting for the winter months until we break ground on our lot in the spring. After our 4 month tiny house experiment, 2600 square feet feels uncomfortably luxurious. In fact we are not using most of the upper floor. While we love it here and are grateful and appreciative to have the opportunity to rent here, 2600 square ft is too much house for us!

Our Santa Rosa house was 1800 square ft. We wanted to build “something smaller than that”, whatever that exactly meant was vague and debatable on any given day. There were parts of the Santa Rosa house that were underused (we are not formal living room and dining room people, and did not need a third bedroom or second bathroom). But the house lacked a few features that are incredibly useful for homesteading and rural farming life (Root cellar anyone? Mud room?). And since we spent a lot of time in the kitchen processing the harvest, fermenting, canning, baking bread and just plain old cooking, the kitchen and pantry area took priority for us.

The design that we have arrived at after countless hours and modifications is a two story house (yes, we too violated rule #1!).  It will also take advantage on the lovely Katywil slopes and be oriented south facing. The main living area will be up top and incudes a mud room (yay, finally!), combined kitchen/living/dining space and a flex room. Like all the other Katywil houses our house will have “aging in place” and the house will be wheel chair friendly so the flex room can be used as a bedroom when grandma comes to stay or if any of us should ever be injured. There is also a bathroom upstairs for the same reason. The walk out basement on the lower floor consists of 2 bedrooms, a bathroom, root cellar (yay!) and utility/mechanicals/laundry room. Total living square footage: 1100. We will be spending the winter months combing over the house specification and materials details, heating system design etc so that we can break ground as soon as possible in the spring.

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