Week 3 - Too cold to do much

No concrete happened this week and neither did much else — my guess is that the cold had something to do with it. The temperatures were in the teens and the single digits all week. Still, I’m amazed at what the crew accomplished despite the frigid temperatures.

Kinda looks like a trash dump at the moment, but if you look closely there are a couple of interesting things to see. Look beyond the tarps; they are just protecting the foundation from the snow flurries we’ve been experiencing. You can see what appears to be a layer of dirt deposited into the EPS foam container; this is actually more of the structural fill. Underneath the structural fill are buried the sewage lines and water piping to the kitchen (to the right, in black) and the first floor bath (toward the back, in black). The new white pipe off to the left is the radon mitigation pipe that will run up to the attic. This pipe connects to a series of perforated pipes imbedded under the structural fill that will serve to collect any radon gas that might build up under the concrete floor and vent it to the roof. The gray piping in the middle is the conduit to the electrical panel.

Week 2 - The foundation and a beaver update

The flowable fill

I got a text on Wednesday from my neighbor Jesse saying “concrete!” and I dropped the grant proposal I was editing and raced over to the lot. When I showed up, though, I realized that it wasn’t concrete — even though it looks like concrete and the truck probably looked like a concrete truck — it was the flowable fill.

What’s flowable fill? Here’s a closeup. It’s a thin layer of cement, sand and water mixture that provides at flat, smooth and void-free surface. It’s not as strong as concrete, but doesn’t need to be: it’s simply a more convenient option than trying to smooth out the base layer of structural fill (the compacted sand/gravel mixture). The various pipes that you see sticking up are the electrical lines and water lines (in the center), the sewage drain (on the right) and the conduit for phone, electricals, cable and some other mysterious stuff that I don’t know about (on the left).

Here’s the cross section of the whole foundation, called a frost-protected shallow foundation (FPSF). More info is available in an article written by Alan Gibson, co-owner of GOLogic. Alan describes the cost savings of a slab foundation, the site preparation requirements, the foam insulation requirements and the technique for pouring the concrete.

Beaver update, bad news

It was such a nice day that I took a walk down to the brook to check out the amazing tulip trees (Liriodendron) that Vivienne had told me about. The beaver dam is still holding up, even through all the rain, snow and cold.

To my horror, I discovered yet another disaster wrought by my ungrateful squatters, the beavers. Two magnificent willow trees by the road have been chewed all the way around the base their trunks. Vivienne says this will likely kill the trees, as the layer of wood directly underneath the bark is the layer through which the tree’s nutrients are transported. So sad. Thankfully, someone has saved the other trees nearby by installing chicken wire, but I suppose they figured that the willows are a lost cause.

The EPS foam is in place

On friday, Bruce (the carpenter) and Jim (his helper/painter) installed the Expanded Polystyrene (EPS) foam.

They fit the foam pieces together like a jigsaw puzzle on top of the flowable fill and reported that it was relatively easy to set everything in place. The 8" thick foam pieces are apparently heavier than they look. The raised side wall will insulate the side of the concrete slab while also creating a bowl in which to pour the concrete. You can see that half of air-vapor barrier has been laid down already. Next week, hopefully, we’ll get to pour the concrete.

Week 1 - Prep for the foundation

The undisturbed building site

Luckily, a bunch of snow and a thick layer of grass have served to insulate the ground from the cold and have kept it from freezing, even through the recent cold spell. The picture above shows an image of the future location of the residence. See those red bushes? Multiflora rose: worst plant ever; invasive plus thorny plus big and strong equals bad news. I’ve been fighting with it for the past half-year. I had to clear it from around the site and from under the apples trees.

Which way is south?

The whole house design hinges on a south facing structure, as outlined in our last post. Unfortunately, you can’t just use the compass in your iPhone to figure out which way is south. A compass points to the magnetic south (which is strangely enough the north end of the earth’s magnetic dipole), but we want to point the house toward the sun — midway between sunrise and sunset — often referred to as “solar south.” This will ensure that the south face of the house is exposed to sunlight symmetrically — the same amount of sunlight in the morning as in the afternoon.

Mary and I went out to the lot at midday (which happened to be at 11:45 AM, halfway between sunrise and sunset), and we put the thin green stakes in the ground in line with the shadow cast by sun, as shown above, to indicate the direction of solar south. Then Kyle (the builder) and I placed the wooden stakes with orange streamers at the four corners of the home. It looks so small! That’s what went through my mind when I saw the 26’ by 26’ square, the location of the outside corners of the walls. I wonder if it will feel too small when it’s finished. Oh boy.

We angled the house slightly westward to help avoid looking directly at the neighbor’s home. Matt (the architect) believed that the exact angle south wouldn’t significantly affect the solar heat gain.

It begins!

Here’s the progress, taken the week of January 7th, complete with fun tractors and big piles of dirt. We’ve broken ground!

A shot of the cleared ground under the foundation. The topsoil was removed and the remaining soil was compacted. You can see how the water, sewer, electrical, PV and communications conduits and stub-ups are already set into place. Hay with black plastic on top are keeping the ground from freezing.

The EPS foam has been delivered. Once the structural fill is put down over the compacted dirt, the EPS foam will be laid down and will serve as a container in which to pour the concrete. The resulting concrete slab will be the downstairs floor inside the home.

Hello neighbors postcards!

Some of my new neighbors might be curious about the activity on their street, so I made up this postcard that Ill drop in their mailboxes. I thought it would be nice to let them know whats going on, but really Im interested in getting started on my ambitious plan of world domination — by convincing everyone to live in ultra-efficient tiny houses!

Here are some of the most striking energy efficiency features of the Potwine Passive House, as listed in the postcard. Ill talk more in depth about these in future posts.

What is a passive house?

Originally popularized in the seventies by back-to-the-earth types, the passive house concept didn’t hit the mainstream until the early nineties when Professors Fiest (Lund University, Sweden) and Adamson (Institute for Housing and the Environment, Germany) took up the concept in earnest using a strictly scientific approach. The central thesis is that the greenhouse effect can be exploited in buildings to provide most of their heating needs. So much heat is available from the sun, in fact, that the original idea involved generating all of a building’s heat from the sun — hence the name passive: no active or mechanical processes would be required. A building would simply take care of its own temperature inherently, reminiscent of the clever designs of ancient buildings that functioned astonishingly well without a modern furnace or air conditioning. Today’s passive homes use many active mechanical systems like air conditioning and air ventilators, but the majority of heating comes passively, from the sun.

South facing windows are the critical source of heat

South facing windows can capture a tremendous amount of the suns energy in the winter while the sun is at a low angle in the sky. In the summer, when the sun is at a high angle in the sky, an overhang blocks light from hitting the windows to prevent excess heating. Windows facing west, east and north are kept to a minimum, if possible — they will lose heat while adding little solar heat gain. The challenge is to keep the south facing part of the building livable: too many windows will generate too much heat during the day and lose too much heat at night. We want just the right amount of south facing windows to generate enough heat, but no more.

R6 insulated triple pane windows make a huge difference

Windows are terrible insulators; they incur the greatest heat loss in most buildings. Increasing the insulating capability of the windows will result in enormous energy savings.

The actual amount of heat loss expected from a given type of window is quantified by a metric called the U-value, a measure of how much heat is lost per temperature difference between the inside and outside. A good double pane vinyl window will have a U-value of 0.37, given in the (stupid) US units of [Btu/hr SF ℉]. We’ve elected to go with German Kneer-Südfenster triple pane UPVC windows with an amazingly low U-value of 0.167, lower by more than half the U-value of a typical double pane window! This means that our triple pane windows will be retaining more than twice as much heat compared to double pane windows, and this will make a huge difference in energy savings.

The U-value is the inverse of the R-value, the common metric for insulation. Converting the U-value to the R-value of our windows gives an R-value of R6.

Concrete thermal mass foundation stores heat for the night

What happens at night when the sun goes down and it is cold outside? We want to be able to store the heat gained during the day and use it at night. That is, amazingly, exactly what the concrete slab foundation will do! The foundation of the home consists of a concrete slab sitting on top of a layer of insulating foam. The concrete serves as a huge reservoir for heat, helping to keep the temperature constant inside the home by absorbing heat during the day when the sun is out, and by releasing heat at night when the temperature inside cools down. The slab is insulated from the ground to prevent stored heat from escaping through the earth. The trick is to figure out how much concrete is needed to absorb a sufficient amount of energy during the day to keep the home warm at night. Too much concrete will never allow the home to get warm. Too little concrete will never be able to keep the home warm all night. The architect uses an energy model to decide how thick to make the concrete slab.

R50 insulated prefabricated wall panels

The walls are put together in a new and interesting way that helps lower cost, save time and reduce air leaks. Huge wall panels are prefabricated ahead of time in a factory setting, shipped to the building site and then hung on the frame. The installation process only takes a couple of days. The huge size of the panels minimizes the little cracks and seams that cause air leakage in traditional walls. The panels are called Structurally Insulated Panels (SIPs). The SIPs are 8" thick. A normal 2"x6" wall is added to the interior of the SIPs and filled with blown-in fiberglass, resulting in a super insulated wall assembly with an astronomical R-value of R50.

Heat recovery ventilation keeps the air fresh

A typical home leaks a lot of air to the outside. It’s equivalent to leaving the front door completely wide open! In many cases, the leaks are there by design: they bring in fresh air. But when a home is tightly sealed, things will get stinky pretty quickly unless you have a way of ventilating the place. The problem is that you can’t just open a window because you’ll lose heat (or cold) and defeat the whole purpose of tightly sealing the home. The solution is absolutely ingenious: a Heat Recovery Ventilator (HRV). The HRV brings fresh air into the home and simultaneously exhausts stale air to the outside, yet miraculously doesn’t allow heat to escape. I’ll explain how this works in a future post; it’s very clever.

Drain water heat recovery saves hot water

Hot water is a tough issue to solve. Heating up water requires a tremendous amount of energy. Many choose to employ natural gas water heaters, which are probably the most economical option (at least until the natural gas bubble bursts). Our goal is to go fossil fuel free, so we had to consider other options. In a future post, I’ll talk about why we ended up choosing on-demand tankless water heaters instead of solar thermal hot water or a heat pump water heater.

For the moment, however, let me tell you about one of the really cool aspects of our hot water system. Think about what happens when you take a shower. Hot water pours over your body and disappears down the drain. All that energy goes into heating the hot water, but most of the energy is immediately waisted down the drain. Enter the Drain Water Heat Recovery (DWHR) pipe: a drain pipe that recovers most of the heat in the water flowing down the drain and magically transfers it back to the inlet of the water heater. The operating principle is similar to that of the HRV.

LED lighting saves electricity

LED lighting represents a dramatic improvement in lighting technology, providing higher efficiency than incandescents, better color than fluorescents, dimmability and cost savings over the ridiculously long 40 year life of the bulb. Like most energy efficient options, the upfront costs are high, but you save money in the long run. We are outfitting the house with PAR30 (short neck) LED track lights. These bulbs are larger than your standard GU10 or MR16 halogen replacement track light bulbs, but they provide more light, are cheaper and are more efficient. A 12 Watt PAR30 LED replaces a 75 Watt halogen bulb, saving an amazing 84%!

Other cool features

Check back here to find out more about the other fascinating energy saving features of the Potwine Passive House, including:

• An efficient box-shape building structure that retains heat extraordinarily well
• A bunch of clever space saving architectural elements that make a small home appear more spacious
• A 4kW solar photovoltaic (PV) array that will provide 100% of energy
• Tankless on-demand water heaters from Stiebel Eltron, providing instantaneous hot water that never runs out, all in a tiny package at a low cost
• An efficient Fujitsu heat pump, providing heating or cooling in one unit, at an efficiency more than two times that of a conventional heating system
• An efficient heat pump dryer, more than twice as efficient as a conventional dryer
• An efficient induction stovetop that boils water faster (while using less energy) than any other stovetop
• An efficient steam oven that will cook a whole chicken in 20 min!
• A recirculating range hood from Vent-a-hood
• An eMonitor energy monitor that tracks the electricity usage of every circuit in the home

It’s not just a bunch of cool gizmos

Overall, I want to point out that the home is not just a bunch of really cool technological gizmos. It’s a fundamentally new approach to assembling a building. Beginning with the concept of using solar heat, most of the other features derive from this simple first step: a lot of insulation and a tight building envelope to hold in the heat, an HRV to bring in fresh air without losing heat, and a concrete slab to store the heat for later. The second important aspect is the elimination of fossil fuel combustion in favor of electricity. It just so happens that things that use electricity are way more efficient than things that burn fossil fuels. We benefit from this increased efficiency when we install the PV system, which will be much smaller than it would have been without all the super efficient components listed above. In a nutshell, it’s a smarter, more holistic approach. That’s how we expect to achieve a home that uses 8 times less energy than the typical Massachusetts home.