Building Details

I've written this summary of our building elements for construction-neophytes (i.e. Andrea in 2009). I'll eventually write up a detailed version of this page for green-building geeks, but in the meantime you can glean the basics right here.

I-joist framing

If you don't know anything about construction, the first thing you should know is how a stud wall is framed.

Studs are lined up vertically along a sill plate (the bottom piece of wood), and you put insulation inside the gaps. Most new houses these days are framed using 2x6 studs. This is a step forward from old-school 2x4 construction, because you can stuff more insulation inside a 6″-deep wall (technically it's 5½″ deep, but it's still called a 2x6). When residential builders started selling 2x6-framed houses, they trumpeted how this meant greater energy-efficiency.

For a while we were planning on building with 2x6 studs, but our structural engineer advised us to switch to 9½″ I-joists to provide better wind resistance. This gives us four more inches of insulation space, but that's just the start. First, we'll improve the in-wall insulation by using blown-in cellulose instead of fiberglass batts. Cellulose and fiberglass have similar R-values (thermal resistance), but cellulose is more tightly packed and allows less air to pass through walls. This makes it surprisingly fire-resistant, even though it's made from recycled paper, because fires need air flow as well as fuel. It's also treated with borate which makes it resistant to fire, insects, and mold.

Exterior rigid foam insulation

So we'll start with 9½″ I-joist walls, but then we're going to beef it up with another 4″ of rigid foam insulation outside (polyisocyanurate). This will help with air infiltration and reduce our risk of in-wall mold and rot. It will also keep the outer flange of the joist relatively warm, which will mitigate the risk of moisture accumulation (and rot) during cold weather.

[ Update: If we were building the house now instead of in 2011, I would use rigid mineral wool instead of polyisocyanurate. The R-value is a little lower, but I suspect 4" would still be enough to protect our walls from condensation. Unlike polyiso it is inherently fire-resistant, so it doesn't require any alarming flame-retardant chemicals, and since it's not a foam product it won't lose any R-value as the blowing agent leaks out. ]

Mechanical fresh-air exchange

If you're new to green building you may be thinking, "But a house needs to breathe!" Yes, a house needs fresh air, but we'd much rather control the process than just let the house leak heat all the time. So we're following the Passivhaus principles and sealing the house as tightly as possible, but then circulating fresh air using a heat recovery ventilator (HRV) and an energy recovery ventilator (ERV). The reason we'll have both is because the house has an attached meditation retreat cabin which will have its own HVAC system.

Heat/energy recovery ventilators draw in fresh air from outdoors, but they transfer a high percentage of the heat from the outgoing air. That way we won't lose a lot of heat with each air exchange.

We installed a Zehnder ComfoAir 350 with an HRV core, but we're considering getting an ERV core instead since the house is getting rather dry in winter.

No central furnace

With so much insulation and wall-sealing, we won't need a central heater to stay warm. Instead we installed a mini-split heat pump — a Mitsubishi HyperHeat FE12 (12,000 BTUs) — to add warm or cool air as needed.

We'll also pick up no small amount of heat through our large south-facing windows. We're employing passive-solar building techniques to maximize winter heat gains while keeping summer gain to a minimum. The glass will have a high solar heat gain coefficient in order to give us the most bang for our sunshiny buck.

All-electric appliances

Now that we've eliminated a furnace, there's no pressing need to have combustion inside the house. The problem with combustion is that it gobbles up oxygen, which increases the amount of fresh (cold) air we need to bring in. The HRV is efficient, but it's not as efficient as reducing our air-exchange requirements.

At first it was disappointing to realize we shouldn't have a gas stove, but then we were introduced to the magic of induction cooktops. I'll probably do a blog post about induction cooking, but the summary is that it has the responsiveness of a gas range but with much less wasted heat. And fashion-forward foodies love it -- take a look at this video comparing induction and gas cooking.

Standing-seam metal roof

standing seam metal roof

Another advantage of eliminating combustion in the house is that we won't require a chimney. This means we might not require any holes in the roof at all (for the plumbing stack we're hoping to use studor valves, subject of an upcoming post). Without any holes for chimneys or skylights our roof could last a long long time without needing replacement, so we might as well do it right.

Standing-seam roofs are normally quite expensive, but I'm hoping the simplicity of our roof will get us a good price. It is basically just a big rectangle with no ridges, valleys, dormers, or gables. All the sheets of metal will be the same length, so it ought to be dead easy to build.

Photovoltaic panels

By not having any gas appliances, we are setting the stage for a Net-Zero Energy house. This means that if we can generate enough electricity on-site using solar panels, we'll produce as much energy in a year as we end up using. We won't be able to generate lots of electricity during the winter, due to solar angle and snow cover, but during the summer we can make up the difference. The house will be connected to the power grid, and ideally the meter will run backwards during peak production.

Due to some challenges on our building site, we weren't able to orient the roof entirely to the south. This means we don't have a huge area for solar panels. But we're building a south-facing awning at the top of the roofline, and that will have enough room for 3.96 kW of solar panels. Not too shabby!

LED lighting

LED lights in Stockholm hotel

Have you ever been in a dorm room lit by a string of Christmas lights instead of the obnoxious fluorescent lights in the ceiling? They create a lovely ambiance and a good background level of light, which can then be supplemented with reading or task lights.

Ted had the clever idea to light our house that way, with hyper-efficient LED strings tucked behind a valance. The best part is that we can add an RGB controller and set the lights to whatever color suits our mood! We stayed in a hotel like this in Stockholm, and it was really cool. We can always set it to white, but why not play around with different colors on pale/neutral walls?

[ Update: We postponed our LED plans and mostly installed traditional fixtures but used Philips A19 LED replacement lamps. ]

For task lighting we'll probably install recessed cans with PAR30 LED replacement lamps, which shine at a friendly color temperature and should last for many years.

Flooring

I've found a few good local sources of sustainably-forested hardwood flooring: a Vermont supplier of maple flooring and a co-op in Western Massachusetts that sells FSC-certified wood floors. We haven't made a decision yet, but we're definitely in the right part of the country for this sort of thing.

Interior finishes

Initially when people asked me what kind of kitchen counters we're going to install, I'd say "Plywood with contact paper." My theory was that you can always upgrade your counters, but it's a lot harder to upgrade windows or other structural components. But then I realized it's wasteful to put in something cheap and rip it out later, plus we need to get a mortgage on the house, so we ultimately installed honed Virginia Jet Mist granite counters. They are quarried in the US, so the shipping footprint wasn't as bad as most granite counters (which often come from India and other distant lands). We're quite happy with the counters so far, and I'm optimistic that they'll last as long as the house does.